Professor, S Boussena

C Locatelli

The bases of a new organisation of the Russian oil sector: between private and State ownership

Keywords: Oil industry, Russia, Ownership rights, Access to the natural resource, State policy, rule of law, market reform, Russian international policy

The reforms and privatisation programmes of the 1990s structured the Russian oil industry around a few large national and private companies. This organisational structure poses some questions in respect of the Russian authorities will to take back the oil sector. Three factors may explain this evolution. First, the Russian authorities want to ensure the long-term future of the oil industry by encouraging new strategies in exploration. Second, the government can use the oil sector to support economic growth. This would involve sharing out the rent in a different manner. Third, and it is e new but important factor, the State intends to use Russia's oil power in this international relationships with the United States, Europe and Asia (China, Japan, South Korea, and India). The future of the Russian oil industry has some importance for the stability of the international oil market. Could Russia produce 12 Mb/d and challenging the dominant position of the Saudi Arabia?

The reforms and privatisation programmes of the 1990s structured the Russian oil industry around a few large national and private companies within a network of complex power relationships with the Federal State and the Regions. However, the struggles between Yukos and the Russian government throughout 2004 cast doubt on the durability of such a structure.

The main aim of this article is to underline the fundamental principles of the new Russian oil policy, those that will structure its future organisation. Our conclusion is that the changes brought about under the wing of the Russian authorities do not seem to be aimed at calling into question the main objective of an oil industry in line with the principal logics, coordinating mechanisms, standards and rules of a market economy. It is in the approach itself that there seems to be innovation. From now on, the State intends to exercise stricter control over this industry by relying on a private sector which would be closely linked with a public sector, and which would respect the "national interest" as defined by the government.

The failure of the reforms, especially with regard to setting up a clearly defined and secure system of private ownership rights, implies the need for a different development model for rent industries from that of a system of private holdings dominated by banks.

There are three main reasons why the Russian authorities want to take back the oil sector.

First, they want to ensure the long-term future of the oil industry by encouraging greater investment in exploration. This would bring an end to the overexploitation of existing deposits. In this respect, the lack of transparency and uncertainty in the institutional environment in Russia has until now cast serious doubt on the capacity of the State to regulate rent industries through classic market mechanisms, from the point of view of both taxation and access to resources. Other logics are therefore necessary. The State seems to choose an "hybrid governance" of the hydrocarbons sector, in which it remains, in the final instance, the authority that coordinates rights concerning the disposal of assets. Second, the government can use the oil sector to support economic growth, which is largely dependent on the hydrocarbons sector. This would involve sharing out the rent in a different manner (more in favour of the State). Third, given the tensions observed in the hydrocarbon markets, the State intends to use Russia's oil power as an international political tool in its relations with the major powers of the United States, Europe, China and Japan. In contrast with the situation over the last ten years, the Russian State now wants to harmonise its oil policy in accordance with the means it effectively has at its disposal and the economic and institutional constraints resulting from its transition to a market economy. These three objectives are not incompatible with a redistribution of the oil rent between different private groups and clans that are close to or useful to the Russian government. The current conflicts surrounding the merger of Gazprom and Rosneft are an indication of the various power struggles affecting the reorganisation of the Russian oil industry. They show that the methods of sharing oil revenues adopted in the 1980s under the presidency of Boris Yeltsin are being challenged.

The revival of the Russian oil industry

As part of the "liberal" approach to transition developed by the Washington Consensus (1) Russian oil industry reform was intended to produce a new organisational model based on different private enterprises. The idea was to redefine ownership rights through vast privatisation programmes, while trying to stimulate competition by breaking up the old Soviet hierarchies. But this reform has not removed the uncertainties about the future of this industry, despite considerable production increases since the end of the 1990s. In particular, the industry has to deal with the major challenge represented by the necessary development of oil-rich Eastern Siberian in light of the gradual depletion of the major deposits in Western Siberia. With the way the industry is currently organised around industrial and financial groups, can this challenge be met?

Restructuring of the oil industry in the 1990s

The profound restructuring that took place in the 1990s led to the emergence of an oligopoly structured around three main groups which replaced the hierarchical centralised organisation of the Planned Economy (2) . The first, which accounts for most of the country's oil production (72.6% in 2003), is formed by private industrial and financial groups. It is made up of five large vertically integrated companies responsible for production through to distribution:

Lukoil, Yukos (at least until the end of 2004), TNK (now TNK-BP) and Surgutneftegaz account for 65% of production and over 50% of crude exports. This concentration of the oil industry was brought about by the vast merger movement that took place in the late 1990s when Lukoil acquired 100% control of KomiTek, Yukos acquired 54.2% control of VNK, TNK and Sibneft acquired equal shares in control of Slavneft, and TNK acquired control of Sidanko. Following the Loans for Shares programme of 1995 (3) , most of the shareholders in this group were Russian banks, with nevertheless a fundamental distinction between the companies held by banks "outside" the group (Yukos, Sibneft, TNK-BP) and the companies held by "insiders", that is the banks created by the holding companies themselves (Lukoil, Surgutneftegaz).

The second group is made up of small or medium-sized companies that are not vertically integrated. The last and more heterogeneous group is made up of integrated or non-integrated companies majority-owned by the State (for Rosneft and Slavneft until 2002) or by regional governments (Tatneft, Basneft, etc.). Their share in production however is marginal, with Rosneft accounting for 4.8% of production in 2003 (cf.

Renewal of reserves: a matter of growing concern

The significant differences between the various estimates bear witness to the uncertainties characterising the Russian oil industry despite the sweeping reforms of the 1990s. The factors that have enabled production to increase since the beginning of the 2000s are disappearing.

Future increases in output (or even maintenance of present levels) will depend on implementation of development policies different from those that have driven the revival of this industry. Consequently, this new approach will require other types of strategies from the main private actors in this sector.

The period of intensive exploitation of existing deposits

Most of the additional output of the last few years can be attributed to two main sources: oil that was not extracted during the transition period in the 1990s (in 1994, 28% of Russia's oil wells had ceased production), and oil left in the ground because of the extraction practices of the 1980s. In other words, the increase has come from the rehabilitation of existing deposits (4) .

Thus, the additional 2.4 Mb/d produced between 1999 and 2003 came from deposits already being worked at the end of the soviet era.

The strategy of maximising production and thus of rehabilitating (the most profitable) deposits during the Soviet era was accompanied by very low investment in exploration, riskier strategies and longer time frames. Investment in exploration has been falling steadily since the early 1990s (5) . Despite individual differences among them, vertically integrated companies have invested very little in exploration. Between 2000 and 2002, less than 2% of investments made by Yukos and Sibneft were in exploration. In the case of TNK, this figure was 5% (6) .

Only Surgutneftegaz and Lukoil have maintained a real strategy of investment in the exploration of new oil-rich areas (7) , which they did even during the period of reorganisation -Cash stripping

This situation was brought about by the behaviour of actors born of the privatisation movement. These companies have adopted a short-term strategy of seeking immediate liquidity by maximising exports in order to rapidly increase the value of current assets. This strategy is known as cash stripping. The strategies of vertically integrated companies are characterised by two aims: maximisation of exports, which is a way of obtaining a much higher unitary income than that obtained from domestic sales, and its corollary, maximisation of production. The substantial increases in oil production over the last three years enabled Russia to boost its exports from 2.90 Mb/d in 2000 to 4.98 Mb/d in 2004, although exports to Europe have always been high despite the decline in production between 1990 and 1998.

-Significant differences depending on the type of vertically integrated company Such strategies expose the development of the oil resource to stripping practices, particularly when the main shareholders of these private companies are "outside banks". The essentially financial rationale of these private groups means that their sole concern is financial performance, their aim being to increase the value of their shares. Management of the oil industry is thus extremely unbalanced, with investment being made in enhanced recovery techniques to produce oil from the most accessible resources at the expense of a balanced drilling programme (8) . Companies have increased their reserves essentially through asset stripping made possible by operating huge mergers and creating an extremely concentrated industry. Yukos is the best example of this type of development. This company's increase in production (0.8 Mb/d between 1998 and 2004) has been achieved through use of enhanced recovery techniques to extract oil from the most profitable deposits, while at the same time 35% of its oil wells have closed and investments in exploration are now among the lowest of the Russian oil companies. Furthermore, Yukos has made extensive use of the tax reduction schemes set up by the Federal Government and regional authorities.

Probable long-term effects

Even if we do not wish to enter into the debate over the true extent of Russia's estimated reserves, a few comments should be made (9) . While there is no denying the productivity gains from re-opened wells, the problem of ensuring the efficient management of existing reserves must be addressed. In fact, the increase in output seems to have been achieved without any control from the Russian authorities concerning the conservation of deposits.

If Russian oil production is to increase, or even be maintained at its present level, new production capacity and thus considerable investment will be needed. Two factors in particular are likely to be problematic in this respect. First, the proportion of total proven reserves in all explored reserves, has dropped considerably (categories A + B in the Soviet classification), falling from 67.8% in 1958 to only 26.5% in 2000 (10) . And second, according to the IEA, 60% of these proven reserves are in the "difficult to recover" category (11) . The low level of exploration since the beginning of the 1990s raises questions concerning the start of production in the new oil-rich areas in light of exhaustion of deposits in the large Western Siberian basins.

Unexpected results of privatisation

A key question still remains unanswered today: why has privatisation failed to achieve its stated aim of creating a more efficient and balanced (to ensure its long-term future) oil industry in Russia? Why has privatisation led Russian oil companies to adopt short-term strategies? The principal goal of reform was to create Western type private enterprise and so encourage the development of management methods and behaviour in the oil industry that were more efficient than those prevailing in the Soviet Centrally Planned Economy.

Privatisation was based on two main logics: organisational reform centred on a principle of vertical integration in order to determine the optimum boundaries of a company, along with a redefinition of ownership rights through privatisation.

Uncertainties surrounding ownership rights

The short-term strategies of oil companies, and particularly the lack of investment in exploration, stem from the unexpected results of a privatisation process that has taken place in an institutional environment characterised by weakness of the Rule of Law. Despite a reform programme aimed at establishing a clearly defined and secure system of ownership rights, these rights are still subject to considerable uncertainty. Privatisation of the oil industry has essentially attenuated the former Soviet system of ownership rights, giving holders of private ownership rights temporary and partial access rights to asset ownership (12) .

-Right to sell assets is coordinated by the State Privatisation of the hydrocarbons sector has led to lack of security concerning the right to use assets. First, privatisation processes have been widely perceived as illegitimate. The purchase of shares at rock-bottom prices, the lack of tendering procedures, participation of banks in auctions they themselves have organised and won, and the failure of the successful bidders to realise the investments they were supposed to realise in the company all bear witness to the lack of transparency surrounding these privatisations (13) . Second, manipulation of the bankruptcy law linked to the weakness of the rule of law (in other words the way in which the law is applied) has taken away the traditional function of the bankruptcy process and made it into a tool for stripping (14) . In such conditions, the State does not feel bound to respect ownership rights, as would happen in market economies, the Yukos affair being a good example of this. When Yukos was negotiating the sale of 40% of its shares to ExxonMobil in 2003, the State blocked the transaction knowing that the transfer of strategic assets was at stake.

-Uncertainties over access rights to resources Despite a legal framework based for the most part on Western standards and rules, the way in which exploration and development licences are granted is creating extreme uncertainty over access rights to Russian oil resource. In order to rapidly reorganise and privatise the oil industry, most of the licences granted to companies were not subject to a tendering procedure, as required by law. This practical approach gave a kind of legal recognition to the exploitation of deposits that the Soviet Union had de facto granted to production associations that were used as the basis for creating holdings [START_REF] Oil | Gas Legislation in Russia. From Texas To Siberia : Is a Russian Model Emerging[END_REF] . But at the same time, it offered the State the perfectly legal option of reallocating certain licences. This shows that it was hardly appropriate to transpose the most advanced institutional models of market economies to the Russian environment of the early 1990s.

-Certain doubts surrounding the right to income from ownership Finally, it should be pointed out that the quota system for gaining access to the Transneft transportation network, and thus to export markets, limits access to revenues (particularly in hard currency) given the considerable difference between domestic market prices and those of export markets. In theory, oil companies have had the right to export 25% of their production.

In practice, some of the most powerful (Lukoil, Yukos) have been able to "bargain" for much higher percentages while other companies have been unable to access the Transneft network.

The discretionary practices of Transneft (depending on the objectives of the State) are creating an unstable environment for Russian companies and making any kind of contractual relations largely ineffective.

Sharing the oil rent: a battle between the State and the major companies

The weakness of the formal market institutions has stood in the way of operation of classic market economy mechanisms with respect to the State's retribution as owner of underground natural resources.

In the first instance, the State does not exercise efficient control over its tax revenues. It is struggling to get the large industrial groups to pay their tax debts. The most powerful vertically integrated companies have thus been able to develop a wide variety of tax evasion schemes. The extremely complex structure of certain vertically integrated companies makes it possible to practise transfer prices (16) . This internal pricing system (17) is seen as a way of reducing the tax burden from hydrocarbon sales through offshore subsidiaries of oil companies established abroad. Transfer prices also provide a way of limiting tax pressure in that crude oil prices are undervalued [START_REF] Konoplianik | A single tax on mining resources is applied[END_REF] . The extreme use by some companies (Yukos, Sibneft, TNK) of the tax exemption schemes set up by certain regional authorities (regions of Chukotka, Mordovia and Kalmykia) is part of this logic. The authorities thus organise "offshore zones" within their regions and play a very significant role in these tax evasion schemes.

Second, the State is incapable of setting up an effective taxation system based on the quality of deposits. Yet differentiation is essential to stimulate exploration [START_REF]A taxing question[END_REF] . Nor is the State in a position to specify in detail the exploration and production licences to be granted, since it does not have the necessary information. Information asymmetry between the State and Russian oil companies is particularly marked in this area. Furthermore, in a context marked to a greater or lesser extent by corruption, it would probably be very difficult for the State to implement an elaborate system of differentiated taxation. The use of a single tax, irrespective of the quality of the deposits, at least has the merit of simplicity and, to a certain extent, prevents large-scale fraud.

Why does the State want to regain control of the hydrocarbons industry?

The opacity of the institutional environment in Russia have in the past fundamentally called into question the State's capacity to regulate rent industries through market mechanisms, in particular through the tax system and regulations governing exploration and development licences. The need to orient strategies toward investment in exploration in order to conserve oil resources, a desire to contribute to maintaining high international prices and to redistribute the oil rent to provide a basis for economic growth are factors justifying the State's determination to regain control of the hydrocarbons sector (in a context where market institutions are in their infancy, where the Rule of Law is difficult to implement and where privatisation has not produced the desired behaviour). The State must now define a coherent, centralised oil strategy to serve its goals both at home and abroad.

4.1 Will taking back control of the oil industry provide a way out of the "institutional deadlock"?

The State must attempt to find a way of getting the oil industry out of the "institutional impasse" in which privatisation has more or less locked it. The development of strategies to enable more balanced management of the Russian oil industry is crucial for its long term future. In the Russian institutional context, more or less, this must involve better management of oil production growth (slower?), greater investment in exploration than in the past, and stricter State control over reserves in order to guarantee renewal. A revival of the reform process might have been seen as a way of getting out of this institutional impasse. But such a revival will only come from a compromise between the various interest groups, notably between the State, the large vertically integrated companies and the Regional authorities. In fact, for a wide variety of reasons, it seems that neither the Regions nor the oil companies have any interest in following this path or in strengthening the market institutions (20) . The Russian oil companies have to a great extent tried to maintain a certain opacity in the way they operate in order to ensure that the rent continues to be shared out in their favour. In particular, it was important for them to avoid any legal provision that would imply greater transparency (in term of information) and compliance with fiscal regulations, which may explain the strong opposition from certain Russian companies, notably Yukos, to the production sharing agreement regime [START_REF]Dramatic Changes to Production-Sharing Regime" International Law Office, Energy/Natural Resources[END_REF] . The weakness of the Rule of Law, which allows legal and fiscal regulations to be circumvented and market institutions to be manipulated is something that the dominant actors do not want to see disappear, insofar as the uncertainty and lack of transparency in the institutional environment enables them to conserve their gains [START_REF] Hoff | After the Big Bang ? Obstacles to the Emergence of the Rule of Law in Post-Communist Societies[END_REF] .

-Hydrocarbons at the service of the economy

The State must also arrange with the oil companies for a new way of sharing out the hydrocarbon rent so that this sector can be used to help achieve the economic growth objectives announced by Vladimir Putin. The rent industries must feed the State budget more substantially, in particular via the tax regime, while Russian growth remains largely driven by international hydrocarbon prices. In a study carried out in 2002, J. Rautava showed that a 10% rise in the price of oil would lead to an additional 2.2% increase in GNP [START_REF] Rautava | The role of oil prices and the real exchange rate in Russia's economy" Bank of Finland[END_REF] . According to a recent World Bank report, only high oil prices have in the past enabled Russia to achieve economic growth of over 5.5%. In this context, international prices will have to remain fairly high and Russia must therefore avoid contributing to a possible period of decline in international prices by exporting excessively large amounts of oil.

In addition, Russian oil output is certainly not insensitive to crude oil price levels. In fact, all the "optimistic" production scenarios are based on relatively high prices on international markets. In particular, the gradual shifting of "core" production to Eastern Siberia could lead to a substantial increase in production costs [START_REF]Four main factors are likely to push up these costs: harsher climatic conditions[END_REF] . Consequently, the future of Russia's oil policy is largely tied to a policy in favour of defending prices. It is important therefore for the Russian State to be able to maintain control over oil company export strategies.

-Reinforced control of the oil industry without large-scale nationalisation Today, the Russian State is seeking to strengthen its control of the hydrocarbons sector while avoiding total re-nationalisation of the oil industry. In our opinion, the final objective of a hydrocarbons industry whose organisation and regulations are in conformity with those of a market economy is not called into question as the desire to deregulate trading in Gazprom shares would tend to suggest. Nevertheless, the government's position might appear ambiguous in the sense that it is trying to reconcile contradictory goals. The challenge is thus to create a system that maximises efficiency through private management while allowing tighter State control in order to set up a market economy that will probably be more in line with Vladimir Putin's vision of Russia's place and role on the international scene.

Stricter conditions of access to Russian natural resources and the State's desire to exercise tighter control over this access are the first important signs that the central authorities are regaining control of the sector (25) . The State's discretionary reallocation of exploration and development licences to companies in which it is the main shareholder (Rosneft, Gazprom) [START_REF]The more stringent conditions for obtaining production sharing agreements are an illustration of this type of control. A. Konoplyanik[END_REF] or which benefit from State support (Lukoil, Surgutneftegaz), and re-examination of the conformity of a certain number of licences concerning major deposits, are part of this movement (27) . This renewed control is also being achieved at the expense of the Regions, which in the past had considerable power in the industry. The 2003 amendments to the 1992 Subsoil Law give the Federal Government (the Ministry of Natural Resources) exclusive control over granting exploration and development licences. Regional authorities simply have a consultative role, whereas in the past they had joint power with the Federal Government to allocate licences (28) . Finally, projects aimed at excluding oil companies not majority owned by Russian investors from tendering procedures to obtain exploration and development licences also show the State's desire to further strengthen its direct control over access to Russian oil and gas reserves [START_REF]State Control Over Lock, Stock and Barrel[END_REF] .

As part this process to take back the oil sector, the State is also creating companies in which it has majority or total control. The final form of the new organisation of the oil industry that the Russian authorities wish to establish has not yet been completely defined. It will depend to a large extent on the current conflicts between the various pressure groups, on the need to adapt to market rules and on Russia's foreign strategy. Pressure will come in particular from international oil companies that wish to gain access to Russian resources, from the United States, from the European Union (to which Russia has always been a major hydrocarbons supplier), from Russia's desire to become part of the world economy (the G8, WTO). The new role that Vladimir Putin's government intends to give to hydrocarbons in the country's relations with its major partner countries will also be an important factor. A number of questions already arise. Will there be one or several companies in which the State has majority control? Will Gazprom and Rosneft be at the centre of the arrangement, a matter that would seem creating conflict between two groups of pressure within the government? (The Gazprom-Rosneft merger, though problematic [START_REF] Gazprom | the merger of Gazprom and Rosneft while[END_REF] , must increase the State's current 39% share in Gazprom to 51% in the combined company (31) ). What will be the place in this organisation of Yukos's main production unit, Yuganskneftegaz, bought by Rosneft in December 2004 following initiation of bankruptcy proceedings against Yukos? Last, the role that foreign investors will be allowed to play is a major unknown. Even if foreign oil companies are not excluded, they will very likely be subject to restrictions or at least to the approval of the highest authorities in the country.

Finally, the government intends to maintain control over the exports of the Russian oil companies. This means reinforcing its control over export networks via Transneft, a Stateowned company [START_REF] Gorst | The Energy Dimension in Russian Global Strategy : Russian pipemines Strategies : Business Versus Politics The James A[END_REF] . Rivalry between Transneft and the Russian oil companies over pipeline routes implicitly involves the important stake of the export capacity of these oil companies. It is a question of restricting, as far as possible, the construction of private pipelines that would be owned by the oil companies.

4.2 International aspects of the Russian oil strategy [START_REF] Boussena | Vers une plus grande cohérence de la politique pétrolière de la Russie ?[END_REF] In addition to developing the oil sector, the policy of the Russian authorities appears to be increasingly aimed at setting up a coherent centralised strategy that instrumentalises the sector henceforth considered as providing a "comparative advantage" in international competition.

At the international level, in a context where world energy supply is strongly constrained, Russia can use not only its oil but more importantly its gas resources to play a major geostrategic role with respect not only to the European market, where it has a determining influence, but also to the major Asian countries (Japan, China, South Korea), and even the North American market. The Russians are seeking to exert their influence through a strong presence in the supply sector for the large European and Asian markets.

Gazprom has now clearly established its intention of defining a truly global strategy (34) . It is a matter of maintaining or even increasing its market share in the European Union and positioning itself on the Asian and even the US markets. On the one hand, Russia can play on competition between Europe and Asia in its role as a reliable source of supply for liquids and natural gas alike. On the other, it is also tending to bring the major Asian players into competition with one another in its programme to develop the resources of Eastern Siberia. Furthermore, with the globalisation of the natural gas markets, Russia can undoubtedly aspire to a decisive role in price formation for this commodity. In a context where there are tensions in world oil supply (and even gas supply in the case of the United States), Russia undoubtedly has a trump card to play in the context of the proposed "strategic partnerships".

From this point of view, hydrocarbons represent a structuring element in the country's foreign policy with CIS members, its "near abroad", but also with the southern European countries and those of Eastern Europe. The major Russian energy companies must be the principal vectors of this strategy, through a policy of internationalisation. Gazprom and Lukoil are increasing their presence in these areas by securing holdings in companies undergoing privatisation or through joint ventures (35) . This is particularly true in central Asia and the Caspian region, which enhances the complementarities (rather than the oppositions) between these two zones. The numerous agreements signed between Russia and Kazakhstan, particularly with regard to the transport of Kazakh oil through Russian territory, the "calls" from Russia to coordinate the oil policy of the two countries [START_REF]Kazakhstan oil to flow east[END_REF] , demonstrate the extent to which the Russian State intends to "reinvest" the economic space of central Asia and expand its influence in the region (37) . This international policy could also explain the redeployment and multiplication of the interventions of the Russian oil companies (close to the State) in other oil producing regions, notably in the Middle East and North Africa (38) .

***

The State's attempt to regain control of the oil sector is an important new factor in the development of the oil industry, as it could lead to greater control over production, oil exports and renewal of resources. This recent combination of public and private forms of governance in the industry can be seen as an attempt to get out of the institutional deadlock in which this sector has found itself since the privatisation movement. It reflects the incapacity of the State to regulate a rent industry via the classic institutions of a market economy, whether they be tax regimes or regulations governing access to resources and development of deposits.

Privatisation alone has not allowed consolidation and security of ownership rights. The major private players have had an interest in maintaining institutional uncertainty in order to increase their share of revenues.

This renewed control also raises a number of crucial questions. While the final goal is to set up a market economy that is totally integrated in the world market, a transition phase is now opening up. The conditions and form of this control have yet to be defined, particularly concerning the creation of a large hydrocarbons company with majority public capital. The general configuration of the oil industry and the room given to international investors remain major unknowns. Finally, can this hybrid model, a sort of third option, serve as a form of governance for the hydrocarbons sector in the transition phase and enable Russia to become truly integrated into G8 and the WTO?

  The differences between China and Japan concerning the first Russian oil pipeline to Asia are an example. Today, the decision of the Russian authorities to choose the Japanese option via Nakhodka, without excluding the possibility of a branch to China, clearly shows the ambiguity of the Russian government's position. These developments are accompanied by bilateral oil supply agreements between China and Russia. Thus, the Chinese company CNPC has advanced a payment of $6 billion in exchange for supply of crude oil from Rosneft until 2010. This source of financing would seem to have facilitated Rosneft's purchase of Yuganskneftegaz. If the Chinese really played a key role in Rosneft's acquisition of Yukos's subsidiary, this would be the sign of a new power relationship emerging on the Asian energy scene. It is also important to underline the new relations that India is establishing with a few large Russian oil companies and in particular its interest in participating in the Sakhalin LNG development projects.

Table 1

 1 ).

	The main Russian oil companies and the composition of their capital
		Companies	Production : Mb/j, 2003	Crude oil
			exportations :Mb/j,
				2004
	Private vertically
	integrated companies
	1. Group owned by Bank	Yukos	1,6	0,6
		TNK-BP	1,2	0,58
		Sibneft	0,6	0,2
	2. Group owned by	Lukoil	1,6	0,59
	insiders	Surgutneftegaz	1,1	0,41
	Total		6,1	2,38
	Majority State or
	Region ownership
	-State	Rosneft	0,4	0,1
	-Regions	Bashneft	0,2	-
		Tatneft	0,5	0,23
	Total	-	8,4	3,7
	Source : Petroleum Argus, 28 February 2005, p. 2.
	During the period of restructuring of the Russian oil industry, production dropped
	considerably, with reductions of 5.3 Mb/d between 1987 and 1998. However, since the end of
	the 1990s, its spectacular recovery (7.1 Mb/d in 2002, 8.4 Mb/d in 2003 and 9.2 Mb/d in
	2004) might suggest that a new development phase is opening up in the wake of the reforms.
	This increase in output brings to the forefront the crucial question as to the "sustainability" of
	such levels in the medium-long term, and at a time when the International Energy Agency
	(IEA) is predicting a sharp downturn in Russian oil growth in 2005.
	1.2 Uncertainties concerning Russian oil production in the medium term
	Forecasts for 2010-2020 vary considerably, ranging from 6 to 12 Mb/d. Private oil companies
	and certain Western experts predict that by 2008/2010 production could reach the record
	levels of 1987 (11.4 Mb/d). But the Russian Ministry of Foreign Affairs predicts slower
	growth, with production of 5.6 Mb/d by 2010. In between these two extremes, we find the
	"moderate" scenario, corresponding to the government's "optimistic" version of the long-term
	energy plan (2020), in which production is estimated at between 8 and 9.6 Mb/d. This forecast

Sources: Annual reports of various Russian oil companies; The Moscow Times, different years, Fontaine (J-M.), Laherrère (J.), Perrodon (A.).-"Le rebond de la production pétrolière en Russie: Quelles perspectives à long terme ? Quelles opportunités industrielles ?" -Revue de l'Energie, n° 538, July-August 2002, p.

421

-432; "World Energy Investment Outlook 2002".-IEA-OECD, 2002; "Putin seizes Yukos shares; Yukos names new CEO" OGJ, 10 November 2003; Khartukov (E.), Starostina (E.).-"Ex-Soviet Oil Exports: Are the Russians really Coming" -MEES 47:4, 26 January 2004, 10 p.

Notes

(1) According to G. Roland, the transition envisaged by the Washington Consensus is based on a combination of neo-classical price theory, standard macroeconomic theory and the experience of stabilisation policies. It is opposed to the more institutionalist view of the transition. For a presentation of the two views of the transition, the reader is referred in particular to: G. Roland, Transition and Economics : Politics, Markets, and Firms (Cambridge : MIT Press, 2000) and W. Andreff, La mutation des économies postsocialistes : une analyse économique alternative (Paris : L'Harmattan, collection Pays de l'Est, 2003), 366 p.

(2) Remember that under the Soviet regime, the oil industry was organised like a government ministry that carried out the classic economic functions of a company. Production was the responsibility of technical production associations that were regulated by the Oil Ministry. In such systems, public or private oil companies do not exist.

(3) The Loans for Shares programme gave Russian banks control of some of the State's shares in the capital of the holding companies for three years in exchange for credit facilities. At the end of this period, the government could take back the shares in return for repayment of the loans. Otherwise the shares had to be repurchased definitively through a tender procedure (which was supposed to open up share trading in the companies). (14) The bankruptcy of Sidanko's main production units in 1999 and their purchase by TNK is a perfect example of this type of procedure. In fact, bankruptcy proceedings are only initiated against "entities" that keep an economic value.


A Havet
email: havet@grignon.inra.fr

X Coquil
email: coquil@mirecourt.inra.fr

J L Fiorelli
email: fiorelli@mirecourt.inra.fr

A Gibon
email: gibon@toulouse.inra.fr

G Martel
email: martel@rennes.inra.fr

B Roche
email: roche@rennes.inra.fr

J Ryschawy
email: julie.ryschawy@rennes.inra.fr

N Schaller

B Dedieu
email: dedieu@clermont.inra.fr

Crop-livestock interfaces established through adaptations of farmers' practices over the short and long term

Introduction

Since the 1960s, there has been a global trend toward specializing and intensifying farming systems in order to produce more. However, several authors [START_REF] Hendrickson | Principles of integrated agricultural systems: Introduction to processes and definition[END_REF][START_REF] Griffon | Pour des agricultures écologiquement intensives, des territoires à haute valeur environnementale et de nouvelles politiques agricoles[END_REF][START_REF] Russelle | Reconsidering Integrated Crop-Livestock Systems in North America[END_REF][START_REF] Wilkins | Eco-efficient approaches to land management: a case for increased integration of crop and animal production systems[END_REF] have denounced agricultural development based on these systems, citing such negative impacts as the excessive build-up of nutrients in soil and water, economic dependency on product prices and a decrease in biodiversity. Conversely, integrated crop-livestock farming systems (CLFS), which combine crop production with animal husbandry [START_REF] Russelle | Reconsidering Integrated Crop-Livestock Systems in North America[END_REF][START_REF] Hendrickson | Principles of integrated agricultural systems: Introduction to processes and definition[END_REF], are now being reconsidered as a means of improving farm and land sustainability [START_REF] Herrero | Smart Investments in Sustainable Food Production: Revisiting Mixed Crop-Livestock Systems[END_REF]. CLFS systems improve nutrient cycles (via exchanges of manure and straw) and are a source of economies of scope [START_REF] Vermersch | L'éthique en friche[END_REF]. They have the potential to bring about diversification in cropping plans, crop rotations and crop and grassland locations [START_REF]L'agriculture écologiquement intensive: nature et défi[END_REF]. This double nature of diversity (of agricultural activities, of resources for production) can be seen from the adaptive capacity point of view (Milestad et al., 2012), i.e. as a source of the farming systems' flexibility.

Most CLFS studies that have been conducted thus far refer to experimental or modeling approaches [START_REF] Ryschawy | Mixed crop-livestock systems: an economic and environmental-friendly way of farming[END_REF]. There is a lack of knowledge on the interfaces between livestock and crop management in farming systems themselves, through on farm studies. The aim of our investigation was to analyze the crop-livestock interfaces in CLFS systems at different spatial and temporal scales, based on the assumption that the ways in which farmers adapt their CLFS farms over time reveal the original crop-livestock interfaces. Adaptive capacities refer to different time scale of dynamic approaches [START_REF] Dedieu | Incertitude et adaptation : cadres théoriques et application à l'analyse de la dynamique des systèmes d'élevage[END_REF]. Long term trajectories of farm-family systems (several decades, at the territory level), reveal the place of the combining of activities within farm's path of development [START_REF] Evans | Adjustment strategies revisited: agricultural changes in the Welsh marches[END_REF] through stabilities, on crisis-induced bifurcations (severe drought, erosion) or opportunities. Medium term (several years) and short term (the chaining of periods within the year) analysis, within one farm development sequence, can show how the CLFS adapt to hazards, prices volatility and climate variability. Calibration of the agricultural system and the functions of different constitutive elements, so as to benefit from buffer capacities on one side and adjustments -regulations on the other, so as to react quickly to irregularities are the two sides of farmers decisions in regard with adaptive capacities [START_REF] Dedieu | Incertitude et adaptation : cadres théoriques et application à l'analyse de la dynamique des systèmes d'élevage[END_REF]. Medium term can also position research on transition sequences: what is at stake is how to engage change, notably here on the way to reduce the use of inputs, to move towards self-sufficiency. All that dynamic approaches applied with farm surveys or with clinical approaches [START_REF] David | Etudes de cas et généralisation scientifique en sciences de gestion[END_REF] of individual farm case will contribute to this paper to analyze crop livestock interfaces: farmers' choices pertaining to cropping plans (dimensioning of crop areas and grasslands) and the spatial location of crops and grasslands, soil fertility management through the inclusion of grassland in crop rotation, multifunctionality of crops, contribution of specific animal batches to the regulation of cropping systems and interactions between crop species combinations and livestock feeding equilibrium.

Materials and Methods

Our paper associates different studies (n = 6) realized in France, that are summarized below. We gather the knowledge produced on each study by identifying several transversal traits of what the on-farm and dynamic approaches lead to, declining crop livestock interfaces.

Materials

Data were collected for 6 case studies covering oceanic, continental and semi-oceanic regions of France, and involving mostly beef and dairy cattle.

Crop livestock as farms paths of development in Coteaux de Gascogne (one case study, CS1): Coteaux de Gascogne (Pyrenean Piedmont in south western France) is an upland area where there has been limited specialization in agriculture. In this hilly region, half of the farms currently use a mixed crop-livestock system including cattle and cash crops, while the others specialize in either crops or cattle. We carried out spatially explicit surveys of all the farms located in four municipalities (56 farms) to assess the local diversity in the farm characteristics and the changes undergone since 1950.

Crop-livestock in intensive farming systems in western France (four case studies, CS2 to CS5): For diverse environmental reasons, grassland conservation or development has become an important issue in livestock farming systems in Western France, especially dairy cattle farms. We studied many dairy farms with different levels of self-sufficiency in terms of their inputs, particularly straw and animal feed. The forage systems of these farms, which are located in intensive arable crop or intensive crop-livestock production regions, are undergoing changes.

-Agricultural specialization in crop production in the Pays de Caux (north western France, CS2) has resulted in erosive runoff. Grasslands are increasingly being recognized as a tool for mitigating this phenomenon. In order to assess the possibility of developing such a tool in dairy systems, we surveyed eight dairy farms and conducted an economic assessment of different farm management options.

-In the Plaine de Niort (western France, CS3), the conversion of grasslands into intensive annual crops led to a huge decline in the populations of Little Bustards (Tetrax tetrax, a heritage bird species). This trend was reversed in 2004 thanks to agri-environment schemes. In order to assess the role of grasslands in production systems, we analyzed: (i) farmers' management choices (24 farms) and (ii) farmers' decisions and adaptation regarding crop choices, crop successions and crop allocation across fields (5 farms).

-In Brittany (western France), the intensification of farming systems has led to farm enlargement and specialization toward animal production (dairy or beef cattle, pigs and poultry). Land use simplification at the regional level has resulted in three main categories of land use: grassland (38% of farm area), maize (26%) and winter cereals (26%) (ASP, 2010). Dairy farmers have developed a variety of livestock farming systems, ranging from maizebased systems to grassland-based systems, which are sometimes combined with cash crops.

We studied the various managements of livestock and grasslands in 21 farms by means of surveys (CS4). We also surveyed 28 pig farms (CS5), some of which incorporate dairy or cash crop production. We explored the links between cropping plans and the origin of feed (bought or produced on-farm).

Transition of crop-livestock toward high levels of self-sufficiency (CS6) (East and West): In all regions of France, farmers may choose to steer their farming activities toward selfsufficient or organic farming systems. This case study deals with the design of self-sufficient and organic mixed crop-dairy systems in the Mirecourt experimental farm (Plaine des Vosges, north eastern France) and two commercial farms that are part of the Sustainable Agriculture Network in western France. The transitions designed by the experimenters and farmers for these mixed crop-dairy systems were analyzed so as to learn how free from inputs selfsufficient systems can be managed.

Self-sufficiency, environmental considerations (erosion, biodiversity), and long term paths of development: the reasons for studying crop livestock farming can be diverse in the gathering exercise we present here. Note two important gradients within the cases:

-various functions of crops production, from crops for cash to crops for cattle or pig feeding (as extremes polarities) ; -self-sufficiency as a primary or a secondary goal for the farming system. In the first case, animal and crop performances are due to the way farmers achieve this primary objective. In the other case, the objective is to minimize inputs.

Methods

In all the case studies, farmers' practices and farm trajectories were analyzed in relation to the framework of the European Livestock Farming System approaches [START_REF] Sibbald | Livestock farming systems research in Europe and its potential contribution for managing towards sustainability in livestock farming[END_REF][START_REF] Dedieu | Système d'élevage, un concept pour raisonner les transformations de l'élevage[END_REF]. Farm management was considered via a global approach, whereby farms are viewed as finalized systems. In such systems, the farmer and his family aim to achieve their own objectives, within the limits of their advantages and constraints, by combining human and biotechnical subsystems and exchanging information [START_REF] Capillon | Typologie des exploitations agricoles, contribution à l'étude régionale des problèmes techniques[END_REF][START_REF] Osty | Fonctionnement des systèmes d'exploitation pastorale[END_REF].

In two of the case studies (CS3 and CS6), we analyzed the planning and adjustment dynamics relating to (i) crop rotation decisions, via repeated surveys [START_REF] Schaller | DYSPALLOC, a model to simulate farmers' cropping plan decisions in their spatial and temporal dimensions[END_REF], and (ii) farmers' practices concerning crop and livestock management during transitions toward more self-sufficient systems [START_REF] Coquil | Systèmes de polyculture élevage laitiers évoluant vers l'AB et l'autonomie : un renforcement des interfaces cultures/élevage[END_REF].

In situation 1 (CS1), we carried out an exhaustive and retrospective assessment of all the farms based on a series of long-term surveys dating back to 1950. We analyzed farm trajectories to identify the 'paths to last' of CLFS systems [START_REF] Ryschawy | Paths to last in mixed crop-livestock farming: lessons from an assessment of the variety in farm trajectories of change[END_REF].

Results

1. 'Paths to last' in CLFS: crop livestock resistance has several causes [START_REF] Ryschawy | Paths to last in mixed crop-livestock farming: lessons from an assessment of the variety in farm trajectories of change[END_REF] have defined five types of past trajectories of change in CS1. Of these, four have been found to lead to mixed crop-livestock systems. The first 'path to last' leading to mixed crop-livestock farming has to do with maximizing self-sufficiency by combining crops and livestock. The second path involves the constant diversification of production to benefit from economies of scope and safeguard the farm against market fluctuations. The other two paths consist in the enlargement and progressive adaptation of the farm to a family-based workforce. The survival of mixed crop-livestock systems associated with these two paths is highly conditioned by workforce availability. Only the fifth 'path to last', which involves enlargement and economies of scale, does not lead to any mixed croplivestock system. [START_REF] Ryschawy | Paths to last in mixed crop-livestock farming: lessons from an assessment of the variety in farm trajectories of change[END_REF] have highlighted the major drivers of change that have influenced the survival of CLFS systems (Table 1). Since 1950, CLFS systems have been marginalized in European agricultural development. The globalization of the market and the orientations of CAP (European Common Agricultural Policy) subsidies have encouraged the enlargement and specialization of farms to achieve economies of scale [START_REF] Ryschawy | Mixed crop-livestock systems: an economic and environmental-friendly way of farming[END_REF]. The importance of the local territorial context with regard to the potential economic advantages of mixed crop-livestock systems has been underlined. In CS1, CLFS systems are considered to be traditional, which has contributed to their survival in the region. Mixed crop-livestock systems are mostly found in unfavorable areas, where economic results are limited by soil and climatic conditions [START_REF] Ryschawy | Paths to last in mixed crop-livestock farming: lessons from an assessment of the variety in farm trajectories of change[END_REF]. Nevertheless, the choices made by the farmers and the values to which they adhere have worked against these driving forces, thereby ensuring the survival of some mixed crop-livestock farming systems.

In view of the current changes in these driving forces, maximizing self-sufficiency and diversifying production appear to be appropriate adaptive capacities for facing the current challenges and maintaining mixed crop-livestock systems in Europe. The paths to self-sufficiency in the dairy CLFS systems that were studied reveal the presence of new crop-livestock interfaces. Such paths increase exchanges between crop and livestock systems to limit recourse to externally bought inputs. The interfaces concern such aspects as the dimensioning and location of crop areas and grasslands, soil fertility, crop multifunctionality, animal batches and crop species combinations in relation to livestock feeding. These interactions were mainly analyzed at the farm level. Both short and medium time scales were considered.

a. Dimensioning of crop areas and grasslands

In CS3, annual cropping plan decisions were found to depend on a certain crop function hierarchy, which is a classification of crops based on farmers' representation of them (Scahller, 2011): (i) priority crops fulfill essential functions for farmers (e.g. incomes, forage providing) and cannot be replaced by other crops; (ii) complementary crops fulfill an essential function but may be replaced by another crop (e.g. maize can be replaced by sorghum); (iii) optional crops fulfill non essential functions in farmers point of view but this function is punctually interesting (e.g. a supplement forage attempted one year, extension of the cropping sequence with winter barley). Examples of functions include 'providing protein-rich forage' or 'providing high-energy roughage', and so on. Annual cropping plan decisions also depend on agronomic constraints (e.g. crop return time) and plot characteristics (e.g. soil quality, distance to cowshed). It appears that the emphasis placed on priority crops is quite inflexible: farmers tend to adjust the area dedicated to priority crops as much as possible, even sometimes by changing the way in which they divide up their farmland into plots.

In CLFS systems, cropping plans are often more complex due to multiyear forages in crop rotations and the fact that plot sizes are smaller than those in arable farms (CS3: [START_REF] Schaller | Modélisation des décisions d'assolement des agriculteurs et de l'organisation spatiale des cultures dans les territoires de polyculture-élevage[END_REF]. In CLFS systems, farmers manage the relationship between crop and livestock production. Any changes in cropping plans are aimed at providing an annual food supply for the herd while taking into account (i) the natural properties of the land, (ii) field pattern functionalities, and (iii) the desire to attain feed and straw self-sufficiency in the system. In herbivorous livestock farming, improved self-sufficiency in feed can sometimes be achieved by increasing the size of plots devoted to forage crops and possibly feed crops. During conversions to organic farming, there is a tendency for CLFS farms to increase grassland areas and decrease other forage and cash crop areas as well as stocking rates (CS6). This leads to cropping plan changes and subtle distinctions between the agronomic potential of the various fields. Conversely, in an attempt to increase their self-sufficiency, many intensive dairy farms (CS2, CS3 and CS4) have replaced grass with maize and, occasionally, winter cereals. Nowadays "protein sufficiency" has become a real issue, but is not something that is always easily attained on-farm (CS6: [START_REF] Coquil | Systèmes de polyculture élevage laitiers évoluant vers l'AB et l'autonomie : un renforcement des interfaces cultures/élevage[END_REF]. In a few cases, rape crops have been developed for this purpose (CS4). In pig farming (CS5), self-sufficiency is often achieved by incorporating more maize in cropping plans.

During the agricultural year, farmers may change their cropping plans. For instance, they may decide to increase their forage stocks for the following year, in anticipation of possible shortages. For example (CS3), at the end of the second hay-cutting period (around June-July), if the amount of stored forage is less than the desired minimum, farmers can change their plans and sow grass in the autumn or the following spring (after a wheat or winter barley crop) instead of sunflower or pea as originally planned. Such a decision may also be made after the third and last hay harvest, once the final quantity of forage available for the next winter is known (Havet et al., 2010a).

In addition to these overall trends, CLFS systems evolve constantly to adapt to certain constraints. Over medium time scales, changes made to arable crops in CLFS farms are affected by the CAP. At the landscape level in CS3, we observed a decrease in the total area devoted to sunflower between the late 1990s and 2006. Before 2003, farmers would grow ryegrass until May, around which time they would harvest it for hay, before ploughing to sow sunflower and obtaining an annual CAP subsidy (direct payments for rape and oil crops). Following 2003 and the CAP reform, farmers started to receive subsidies for grasslands as well; consequently, they now maintain ryegrass for more than one cut per year, motivated by grassland subsidies and the production of forage stocks [START_REF] Schaller | Combining farmers' decision rules and landscape stochastic regularities for landscape modelling[END_REF].

b. Spatial location of crops and grasslands

There are two rationales behind the spatial location of crops and grasslands: on the one hand, in some areas, environmental protection (biodiversity, runoff) presupposes the enlargement of grasslands, and on the other hand, the desire to achieve forage self-sufficiency encourages some farmers to limit the cultivation of drought-sensitive crops like maize in certain kinds of fields (CS3). In making these choices, farmers consent to a potential reduction in the maximum technical performance of their crops and livestock.

In CS3, adaptation to drought is one of the reasons for a decrease in maize silage area and an increase in grassland area. Furthermore, local protected birds require grass for their development. Initially based on a common intensive model in the late 1990s, farms progressively underwent changes and by 2006, four distinct types, which are presented in Table 2, could be identified. This table also shows that the milk production performance per cow decreases when farmers choose to let milk cows graze. Farmers are observed to take into account soil depth when deciding whether or not to grow maize; similarly, the proximity of fields to cowsheds is considered when it comes to sowing grass [START_REF] Havet | Adaptation des exploitations laitières aux incertitudes climatiques et aux nouvelles réglementations[END_REF]. In the same way, we detected, at the landscape level, a certain regularity in the spatial distribution of crops: maize is frequently grown as a monoculture in the vicinity of grasslands, which are traditionally located in deep and humid soils [START_REF] Schaller | Combining farmers' decision rules and landscape stochastic regularities for landscape modelling[END_REF].

The priority in intensive dairy farming is to fulfill the forage requirements of dairy cows all year round. Farmers often use maize silage and grassland grazing at a high stocking rate for periods of varying lengths in spring (CS2 and CS4). Some farmers currently limit the amount of purchased inputs and aim to ensure farm self-sufficiency by including more grassland in their crop successions (80% grassland in the fodder area instead of 60% in conventional systems, for instance in CS2). Their decisions regarding the spatial allocation of grasslands are not only influenced by the possibility of having milk cows graze near cowsheds, but also reflect, in CS2, their stated objective of reducing erosive runoff via the establishment of grasslands in fields located in the pathways followed by surface runoff during heavy rains (Faure et al., 2010). The use of fields on a farm scale is less specialized when converting to organic agriculture (CS6): temporary grasslands are integrated into arable land and crops are integrated into areas that were exclusively devoted to grazing prior to conversion.

c. Soil fertility management by incorporating grassland into rotations

Crop rotations integrating multiyear temporary grasslands or annual arable crops can be positive for plant production. We observed that farmers try to enhance these positive effects at the farm level.

We identified two types of projects involving self-sufficient organic farms (CS6): the first aims to produce milk from grasslands, while the second aims to produce milk and wheat for feed, as well as to attain self-sufficiency in the production of straw for litter. In the first case, the objective of having annual crops is to renew grasslands in order to maintain the system's productivity. In the second case, the cultivation of grasslands meets the agronomic goals of entire cropping systems by breaking annual and multiyear weed cycles and providing the soil with nitrogen and organic matter. Farmers take into account the pertinence of using multiyear grasslands as starter crops: indeed, in tillage management, at the end of a crop rotation cycle, farmers are less concerned about weeding because of the anti-weed effect of the subsequent grassland [START_REF] Coquil | Systèmes de polyculture élevage laitiers évoluant vers l'AB et l'autonomie : un renforcement des interfaces cultures/élevage[END_REF].

d. Multifunctional nature of specific crops

Most of the time, a single crop cultivated in CLFS farms can be used in different ways, for example as forage or a cash crop. Thus, farmers can easily decide to change the function of their crops in the course of the year. Farmers may conduct experiments to test the forage quality of crops that they wish to introduce in their forage systems. While maize is a common forage feed, other crops are less often subjected to functional changes for use as buffers.

In CS6, farmers test the pertinence of cultivating annual crops for animal feed. For instance, fodder beet is used to supplement grazed grasslands in spring; spelt is incorporated in crop rotations on account of its mineral content, which is beneficial to calves. Another possibility is to use arable crops as forage when they are overrun by weeds: this leads to a certain onfarm valorization that cannot be achieved in specialized cropping systems [START_REF] Coquil | Systèmes de polyculture élevage laitiers évoluant vers l'AB et l'autonomie : un renforcement des interfaces cultures/élevage[END_REF].

In CS3, during the spring period, farmers aim to produce sufficient forage stocks for the next winter. As we have seen, forages can be introduced to offset stocks that are found to be insufficient. However, farmers can only make arable crop substitutions, that is, using forage crops that fall under one of four forage categories that seem to be defined according to their reasoning as: (i) extremely high-energy roughage, (ii) roughage that is equally high in energy and nitrogen, (iii) high-energy concentrates that are produced on-farm, and (iv) externally bought high-energy and high-nitrogen concentrates. Therefore, farmers can ensile wheat (category ii) if they find forage stocks of this category to be insufficient, while cultivating wheat primarily for sale, or even for animal feed (category iii) [START_REF] Schaller | Modélisation des décisions d'assolement des agriculteurs et de l'organisation spatiale des cultures dans les territoires de polyculture-élevage[END_REF].

Dairy farmers, for whom maize is the priority forage for milking cows, tend to provide more surface to maize crop than needed. They choose in autumn whether each field is dedicated to silage production or to sale (CS4). This choice is made according to forage needs, maize yields and less according to incomes needs: incomes are opportunities in this case.

e. Contribution of specific animal batches (in slow-growth programs) to cropping system regulations

The quality of forage that is intended for stocking purposes is dependent on the agronomic properties of the fields and on management.

CLFS systems in CS6 are managed in a very adaptive way, with low planning. In one of the farms, the farmer aims to manage the quality of the grass that is grazed by milk cows.

Research on regrowth quality has led to a reduction in grazing refusals by milk cows: a batch of animals with low dietary requirements (heifers, dry cows) is made to graze on these refusals. In CS6 Mirecourt experimental farm, in order to avoid the invasion of temporary grasslands by rumex, animals with low growth requirements, such as heifers approaching the end of pregnancy, graze on infested fields in late summer to limit rumex development all over the crop rotation. Another management aim, that of increasing forage proportion in hay, has been achieved by means of early turnouts of heifers to temporary grasslands i.e. topping. Cutting can thus be postponed for about two weeks, which raises the likelihood of making hay as opposed to grass silage.

f. Interaction between crop species combinations and livestock feeding equilibrium

In CLFS farms that strive to achieve self-sufficiency, crop species combinations depend on the diversity of the selected diet. Farmers make decisions at different times during the agricultural year, or between years. We studied two different types of self-sufficiency: organic farming in Mirecourt with a focus on interannual diversity (CS6) and pig farming with a focus on the impact of an on-farm feed production unit (CS5).

In Mirecourt, self-sufficiency consists in feeding the herd with resources produced on the farm itself (forages, concentrates), and more specifically by: (i) managing arable and forage areas to obtain adequate forages, and (ii) compensating for variations in the availability of crop and forage areas, or interannual yield variations. In intensive systems, crop rotation and forage management strategies (cultivation, harvest or purchase) ensure adequate feed ration levels in terms of consistent energy and nitrogen contents. However, in organic farming, farmers must cope with variations in availability during grazing periods or indoor feeding in winter. Grazing by milk cows is carried out on both permanent and temporary grasslands comprising alfalfa/orchard grass. Given the difficulty in getting milk cows to graze on alfalfa, the experimentators only carry out alfalfa/orchard grass grazing when there is a lack of forage, for instance during drought periods, since alfalfa is resistant to water deficits. They make midterm adjustments for indoor feeding in winter: calves and milk cows have relatively regular diets from one year to another, whereas heifers are fed the remaining stocks and therefore experience more dietary changes from year to year (Table 3). Over the long term, herd size is adjusted through early culling and the sale of animals, which also helps to cope with insufficient stocks of forage and hay [START_REF] Coquil | Conception de systèmes laitiers en agriculture biologique : une entrée agronomique[END_REF]. In CS5, formula feed self-sufficiency is an objective of some pig farms possessing an on-farm feed production unit (FPU). Given that the agricultural area per farm in Brittany is often too small to feed herds, farmers tend to saturate their fields with wheat and maize. Conversely, specialized pig farms without an FPU have more varied cash crop rotations: diversification is justified by the objective of best prices and yields [START_REF] Tersiguel | Déterminants du choix de l'assolement par les éleveurs de porcs en Bretagne[END_REF].

Discussion and Conclusion

Is CLFS a way to sustainability? Our results show that CLFS farms can last over the long term. Increasing the interaction between livestock and crops results in new adjustment practices (e.g. cropping plans changing during the agricultural year), the emergence of multiple uses for crops (for sale or for use as animal feed, straw for litter, to increase the agronomic potential of soil, etc.) and the development of individualized functions for animal batches (e.g. early grazing by heifers for topping grasslands). Such diversification safeguards CLFS farms against hazards and enhances their adaptability, which is a means of increasing sustainability [START_REF] Darnhofer | Adaptiveness to enhance the sustainability of farming systems. A review[END_REF]. However, this only applies to areas where farm production is supported by a nearby production chain. For instance, in CS1, the dairy production chain is being threatened by the decline in the number of dairy farms and if milk collection were to cease, all the CLFS farms in the area would have to stop production for the lack of another outlet. The quest for complete self-sufficiency is another efficient and sustainable method of enhancing the interfaces between crops and livestock. However, [START_REF] Holling | Understanding the Complexity of Economic, Ecological, and Social Systems[END_REF] has established that this strong connectedness, which is linked to decreased resilience, might lead to a certain weakness that would force these systems to be redesigned if an external impact were to prevent interactions from taking place. According to [START_REF] Holling | Understanding the Complexity of Economic, Ecological, and Social Systems[END_REF], it is indeed highly possible that such situations may need to be redesigned.

The diversity of the values of the indicators that were studied calls for a better understanding of farmers' overall decisions and practices. In their study of CLFS farms that took into account economic and environmental aspects, [START_REF] Ryschawy | Mixed crop-livestock systems: an economic and environmental-friendly way of farming[END_REF] showed that CLFS farms are rarely the most ideal systems when compared to specialized ones, but are certainly not the least ideal either, which concurs with previous findings in the literature. They have underlined the importance of the local territorial context in the potential economic advantages of mixed crop-livestock systems. For instance, as crop productivity is limited by soil and climatic conditions, European CLFS farms are mostly found in unfavorable areas. CLFS systems have been marginalized in European agricultural development, and current agri-environmental policies are aimed at providing assistance to mixed crop-livestock farms in favorable areas (CS2 and CS3) rather than unfavorable ones.

The research of self-sufficiency in farms goes also through cooperation between farms and has various consequences concerning biodiversity at landscape level. Studying this level seems a new challenge to better understand CLFS developing. So, [START_REF] Schaller | DYSPALLOC, a model to simulate farmers' cropping plan decisions in their spatial and temporal dimensions[END_REF] have shown that manure and straw exchanges between farms partially determine farmers' choices pertaining to crops and crop successions. Manure provided by livestock farmers allows farmers specializing in crop production to grow spring crops on a large area, over which they may spread this organic fertilizer at the end of winter. The possibility of obtaining straw without having to grow cereal crops allows CLFS farmers to devote a larger area to forage crops and seed oil crops, as well as increase the range of crops cultivated. Otherwise, the effects of a goal of farm self-sufficiency can be opposite at landscape level: diversification and the increasing importance being given to grasslands have positive effects on biodiversity for milk production (CS2 and CS3), whereas feed production units on pig farms does not lead to crop diversity (CS5). At least, [START_REF] Bamière | Farming system modelling for agri-environmental policy design: the case of a spatially non-aggregated allocation of conservation measures[END_REF] have shown that public policies measures that are implemented must be reflected at the level of the landscape field pattern in order to ensure the greatest impact on biodiversity; for instance, Little Bustards (Tetrax tetrax) depends on the location of crops and grasslands at this level.

Our results indicate a large variability in crop-livestock interfaces among farms, even within a given situation. This variability constitutes a valid argument for increasing interdisciplinary research efforts in order to better understand farmers' decisions, taking into account factors such as the organization of labor, social interactions, economic constraints, etc. [START_REF] Gibon | Modelling and simulating change in reforesting mountain landscapes using a social-ecological framework[END_REF]. Moreover, in order to support the development of agriculture in a way that enables production and landscape management functions to be combined within a given territory, this research must be carried out by working in conjunction with farmers, agricultural advisors, policy decision-makers and other rural stakeholders [START_REF] Gibon | Why and how to analyse the potential of mixed crop-livestock farming systems for sustainable agriculture and rural development at landscape level[END_REF].

Table 1 :

 1 Major drivers of change that have influenced the survival of CLFS systems[START_REF] Ryschawy | Paths to last in mixed crop-livestock farming: lessons from an assessment of the variety in farm trajectories of change[END_REF]

	Group of		General economic and political environment	Farm structure	Regional
	factors						location
	Driver of	Market globalization	European CAP orientations	Decrease in	Tradition
	change	Low	Fluctuations of	Production-	Second-pillar	available	associated with
		agricultural	input and	based	environmental	workforce	CLFS
		prices	product prices	subsidies	subsidies
	Impact on	-	+	-	+	-	+
	CLFS survival
	2. Achieving self-sufficiency in mixed crop-livestock systems by enhancing crop-livestock
	interfaces

Table 2 .

 2 Identification of farms with dairy cattle in CS3[START_REF] Havet | Adaptation des exploitations laitières aux incertitudes climatiques et aux nouvelles réglementations[END_REF]

	Type Maize irrigation Grass / MFA (%) Milk / cow (kg)	Milk cow grazing	Maize / MFA (%)
	1	no	35-45	6000-8000	possible	30-40
	2	no	10	8000-9000	not possible	60-80
	3	yes	10-35	7000-9000	not possible	50-80
	4	yes	35-50	7000-8000	possible	20-40

Table 3 :

 3 Interannual variations in diets (excluding grazing) for three batches, in Mirecourt[START_REF] Coquil | Conception de systèmes laitiers en agriculture biologique : une entrée agronomique[END_REF]

				2006/2007			2007/2008
	Harvest	Intake (kg	Dairy	Calves	Heifers	Dairy	Calves	Heifers
	Terms	DM/animal/year)	Cows			Cows
	Wrapped		26	0	1235	270	0	71
	silage
	Hay	Alfalfa/Orchard	1177	394	10	1320	244	272
		grass
		Temporary	0	0	0	590	0	965
		grassland
		Permanent	1390	73	985	700	14	723
		grassland
	Straw		0	0	127	0	0	0


Claudio Rubattu

Member, IEEE Francesca Palumbo

Carlo Sau

Member, IEEE Rubén Salvador

Jocelyn Sérot

Karol Desnos

Member, IEEE Luigi Raffo

Maxime Pelcat

Dataflow-Functional High-Level Synthesis for Coarse-Grained Reconfigurable Accelerators

Keywords: Coarse-Grained Reconfiguration, Dataflow MoC, Functional Programming, HLS, CAPH, MDC, FPGA, Design Predictability, Design Productivity

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I. CONTEXT, BACKGROUND AND MOTIVATION Flexibility and performance are two highly valued properties of processing systems in many application domains. Modern systems include ubiquitous and upgradable devices for IoT or cyber-physical applications that also communicate with cloud infrastructures. These systems must adapt to mutable conditions, while avoiding unpredictable performance degradation.

To boost performance, High Performance Computing (HPC) and embedded systems designers are pushed to opt for Domain-Specific Accelerators (DSAs), built from ad-hoc hardware-coded kernels exploiting parallelism for optimizing performance. Two representative examples of this trend are Amazon Web Services (AWS) and Movidius. On the HPC side, AWS offers FPGAs in a cloud environment [START_REF] Barr | EC2 F1 Instances with FPGAs -Now Generally Available[END_REF]. On the embedded side, the Intel ® Movidius TM Vision Processing Unit (VPU) is a low-power DSA used in smartphones and drones for computer vision and artificial intelligence applications.

In terms of system flexibility, hardware DSAs based on CGR architectures offer flexibility by adapting to variable application parameters. CGR architectures are traditionally composed of a mesh of Processing Elements (PEs) whose interconnections are reconfigured over time [START_REF] Wijtvliet | Coarse grained reconfigurable architectures in the past 25 years: Overview and classification[END_REF] to offer flexibility. CGR architectures inherit from their hardware nature the capacity of executing compute-intensive kernels in an energyefficient way. However, efficiency and flexibility offered do "Thanks to the projects CERBERO (H2020,732105) and PROSSIMO (POR FESR 2014/20-ASSE I), and to HiPEAC (H2020,687698) for a collaboration grant." C. Rubattu and F. Palumbo -University of Sassari (e-mail: crubattu@uniss.it). C. Sau not come for free. Hardware design is a complex and errorprone task, leading to productivity losses, especially for heterogeneous and irregular targets. High-Level Synthesis (HLS) approaches have been proposed to cope with these losses, obtaining design productivity gains by separating functional system verification, performed from a time-agnostic highlevel language, from timed system verification, performed after automatically inferring hardware-specific code [START_REF] Pelcat | Design productivity of a high level synthesis compiler versus HDL[END_REF].

Many HLS tools are now available, such as Xilinx Vivado HLS [START_REF]Xilinx. Xilinx Vivado HLS[END_REF] and Intel FPGA SDK for OpenCL [START_REF]Intel. Intel FPGA SDK for OpenCL[END_REF]. These tools are based upon imperative, C-like, languages. The algorithm to be implemented is formulated as a sequence of instructions operating on mutable data. This choice is motivated by the very large number of developers trained to manipulate imperative languages that have been dominating computer sciences for decades. But, from a hardware perspective, this choice presents two major drawbacks: 1) imperative formulations generally do not distinguish iterations over time from iterations over space, which do not translate uniformly in hardware (the latter do not imply causality and can therefore be parallelized using replication); 2) they implicitly rely on the concept of global memory at the implementation level, which immediately leads to a "bottleneck" on memory accesses [START_REF] Backus | Can programming be liberated from the von Neumann style?: a functional style and its algebra of programs[END_REF]. These drawbacks can be circumvented by relying upon so-called applicative or functional languages in which algorithms are described as a (mathematical) composition of side-effect free functions. This approach naturally fits DataFlow (DF) Models of Computation (MoCs). An application is decomposed into independent processing actors, communicating with First-In First-Out data queues (FIFOs), with no global storage or synchronization. This is particularly true for stream processing applications, processing data "on the fly" and which benefit significantly from CGR architectures-based acceleration, as found in signal/image processing, media coding/compression, cryptography, video analytics, etc. This paper, in Section II, introduces a novel methodology for the optimal characterization of virtually reconfigurable DSAs exploiting a DataFlow-Functional (DFF) HLS approach as an alternative to traditional HLS tools based on imperative languages. The proposed methodology is targeted for heterogeneous and irregular CGR architectures, leveraging on application specific PEs and tailoring the interconnect to minimize FIFOs. For prototyping purposes, and to compare with commercial flows, experiments target FPGA technologies and demonstrate that, thanks to its modularity and abstraction capabilities, the proposed approach guarantees latency predictability (see Section III). Beside we also show (Section IV) that our DFF approach leads to improved performance for DSAs with CGR architectures.

II. PROPOSED DATAFLOW-FUNCTIONAL HLS

The proposed framework is built from two existing tools developed by the authors: the CAPH compiler and the Multi-Dataflow Composer (MDC) toolset. CAPH [START_REF] Sérot | CAPH: a language for implementing stream-processing applications on FPGAs, Embedded Systems Design with FPGAs[END_REF] is an opensource, domain-specific framework for the specification, simulation and implementation of stream-processing applications based on a dynamic dataflow MoC. Applications are specified as DataFlow Networks (DFNs) using a higher-order, polymorphic functional language. The behavior of each DF actor is defined as a set of transition rules using pattern matching on structured data, resulting in improved abstraction capabilities. The CAPH toolchain provides graphical visualization of DFNs; code simulation with trace facilities; and HLS producing SystemC code for simulation and resourcemonitoring purposes, as well as platform-agnostic ready-forsynthesis VHDL code. CAPH provides 1:1 DFN PEs synthesis, but no support for reconfiguration. MDC is a suite for the design and development of heterogeneous and irregular DSAs based on a set of DFNs to specify the desired behavior of the system [START_REF] Palumbo | Power-Awareness in Coarse-Grained Reconfigurable Multi-Functional Architectures: a Dataflow Based Strategy[END_REF]. It builds reconfigurable datapaths, leveraging on a two-step approach: 1) a model-to-model compiler, the Multi-Dataflow Generator (MDG), derives a multi-functional DFN [START_REF] Sau | Reconfigurable coprocessors synthesis in the MPEG-RVC domain[END_REF] starting from a set of disjointed DFN specifications; 2) a dataflow-to-hardware mapper, the Platform Composer (PC), deploys an HDL description of the CGR datapath. Up to this work, MDC was specific to RVC-CAL language and the actor communication protocol was hardwired on the resulting CGR architecture. Now users define custom communication protocols, and MDC accordingly implements the handshake among PEs. MDC provides N:1 DFNs mapping on a CGR DSA, but it does not support PE synthesis.

Based on the described complementaries, this work proposes a fully automated toolchain, integrating MDC and CAPH, for specifying and deploying CGR DSAs. The toolchain architecture is depicted in Figure 1b summarizes the flow steps. (1) Users are required to provide the input set of specifications (N different DFNs) to be accelerated using the CAPH language. Starting from these inputs, three parallel steps take place to i) make CAPH DFNs compliant with MDC through the CAPH-to-XDF parser (2), ii) optimize sizing of the buffer connecting DF actors (3), and iii) generate the target-independent HCL (4). Three more steps come in succession. The N XDF networks produced by ( 2) are merged in a multi-dataflow network (5), which is optimized (6) using the worst case analysis results of (3). Finally, the CGR platform-independent DSA is deployed in [START_REF] Pelcat | Design productivity of a high level synthesis compiler versus HDL[END_REF]. During the merging process ( 5), common actors are identified and connections minimization is guaranteed. In the CGR DSA, combinatorial switching elements are used to access shared modules, this may affect frequency but not latency.

III. PROPOSED APPROACH: FEATURES AND NOVELTY

CGR architectures provide the flexibility needed by modern signal processing applications, while achieving high efficiency through specialization. Their features and granularity are highly varied [START_REF] Compton | Reconfigurable computing: a survey of systems and software[END_REF], and several works in literature address their design issues. Raffin et. al [START_REF] Raffin | Scheduling, binding and routing system for a run-time reconfigurable operator based multimedia architecture[END_REF] propose the ROMA framework for the scheduling, binding and routing of reconfigurable accelerators for multimedia applications. The ROMA architecture is composed of custom reconfigurable PEs and the framework is specific to them, following an approach similar to general purpose devices, thus loosing specialization and, in turn, efficiency. Voros et. al [START_REF] Voros | MORPHEUS: A heterogeneous dynamically reconfigurable platform for designing highly complex embedded systems[END_REF] leverage on a fixed CGR structure that comes along with its synthesis flow, and where 3 different types of PEs can be used for accelerating purposes. Our effort focuses on a more specific problem: we discuss in this paper a flow to characterize and synthesize circuits to be embedded in a DSA infrastructure. MDC has been combined in previous work with the Xronos HLS to offer DFF HLS to build a Xilinx-specific DF-to-hardware design environment [START_REF] Sau | Automated design flow for coarse-grained reconfigurable platforms: an RVC-CAL multi-standard decoder use-case[END_REF]. CGR DSAs can also be obtained with sole HLS, while modeling reconfiguration by hand. State-of-the-art HLS frameworks are typically imperative-based, and most of them are also target-dependent [START_REF] Nane | A survey and evaluation of FPGA high-level synthesis tools[END_REF]. As we are going to demonstrate in Section IV, imperative-based HLS is not the best choice for developing CGR DSAs, differently from DFF HLS. Synflow Studio [START_REF] Synflow | Synflow studio[END_REF] provides a proprietary HLS framework for multivendor FPGAs using the Cx DF language, which does not support ASICs. Platform-agnostic HDL specification is challenging, as the resulting hardware has difficulties to compete with platform-specific code performance. To the best of our knowledge, only two academic flows support platform-agnostic DForiented HLS: the Orcc HDL backend [START_REF] Siret | A codesign synthesis from an MPEG-4 decoder dataflow description[END_REF] leveraging on the RVC-CAL language, and CAPH [START_REF] Sérot | CAPH: a language for implementing stream-processing applications on FPGAs, Embedded Systems Design with FPGAs[END_REF]. CAPH, adopted in this work, has the advantage of using functional programming semantics that, contrary to the RVC-CAL language, removes imperative semantics from actors. The Orcc HDL backend is no longer available, thus it is not possible to compare performance with [START_REF] Siret | A codesign synthesis from an MPEG-4 decoder dataflow description[END_REF].

Performance predictability is important in a design flow. Indeed, knowing the properties, and in particular the latency, of the implemented system at early design stages improves productivity and reduces design effort. This is a key feature of our approach. HLS tools based on imperative languages can only provide IP latency estimates after synthesis when a reconfigurable system is designed. In Vivado HLS [START_REF]Xilinx. Xilinx Vivado HLS[END_REF] this estimate takes the form of a range (min to max latency): the actual value of each single configuration in a reconfigurable case is obtained by running the corresponding mode over the deployed CGR accelerator. The Intel FPGA SDK for OpenCL [START_REF]Intel. Intel FPGA SDK for OpenCL[END_REF] pursues automatic system-level integration (and parallelization) of hardware accelerators complying the OpenCL computing model. As a result, low-level, cycleaccurate pipeline/scheduling information, typical in other IPbased HLS tools, is sacrificed in favor of an annotated dependence graph describing the generated kernel as a combination of blocks. The estimation provided in the graph refers to the types/sizes of load/store units, stalls and latencies, but a nontrivial calculation of the IP latency is left to designers. Finally, optimization is performed by profiling kernel execution, requiring re-synthesizing an equivalent kernel, automatically instrumented with performance counters, to analyze memory access behavior (stall, occupancy, bandwidth).

The key selling feature of the proposed DFF flow is the ability to compute early and accurate latency 1 estimations before synthesis. Such values depend on the critical path length in the DFN and on the maximum number of cycles required for each actor firing. For Synchronous DataFlow (SDF) graphs, both can be computed statically. For non-SDF graphs, CAPH estimates latency running the cycle-accurate code generated by its SystemC backend. The latency of the CGR-based DSA generated by the DFF flow depends on the selected mode only, corresponding to the selected stand-alone networks, since merging does not affect latency. As a result, the DSA can be optimized in terms of latency before synthesis. To the best of our knowledge, neither [START_REF] Raffin | Scheduling, binding and routing system for a run-time reconfigurable operator based multimedia architecture[END_REF] nor [START_REF] Voros | MORPHEUS: A heterogeneous dynamically reconfigurable platform for designing highly complex embedded systems[END_REF] present this predictability 1 Number of clock cycles required to compute all outputs as in [START_REF]Xilinx. Xilinx Vivado HLS[END_REF]. feature, while [START_REF] Sau | Automated design flow for coarse-grained reconfigurable platforms: an RVC-CAL multi-standard decoder use-case[END_REF] handles SDF inputs only.

In general, pre-synthesis prediction offers an additional advantage: developers can focus on the application to be accelerated with an algorithmic-oriented approach rather than a synthesizer-based one. Imperative-based HLS tools require DSE to improve latency. Developers have to deal with the mentioned lack of information and to understand how to exploit both the available #pragmas and their combinations towards best performance. Moreover, code refactoring may also be necessary to achieve optimal latency values. For these reasons, developers must have a thorough knowledge of the synthesizer and a considerable effort is required to obtain an optimized architecture. To conclude, when compared to imperative HLS, the DFF nature of the proposed HLS provides earlier explorations, while offering system predictability and guaranteeing performance, as demonstrated in the next section.

In summary, with respect to the context of CGR DSAs, the main benefits/features of the proposed integrated flow are: 1) Custom PE Generation -Hardware generation considers heterogeneous, HLS-generated PEs for each DF actor, favoring flexibility with respect to [START_REF] Raffin | Scheduling, binding and routing system for a run-time reconfigurable operator based multimedia architecture[END_REF].

2) Reconfigurability Management -DF-based mechanism maximizes and controls resource re-use, leveraging on datapath merging techniques. Moreover, reconfiguration management is guaranteed by MDC.

3) Predictability -Modular specifications facilitate the predictability of system properties. Before synthesis latency estimations can be carried out on the basis of the pre-processed CAPH DFNs. 4) Target Independence and Availability -Both MDC and CAPH are platform-agnostic and open source. 5) Code Readability -MDC and CAPH preserve the correspondence among DF actors and hardware PEs. This is important for example in case of post-HLS enhancements. Vivado HLS acts differently since it assigns IPs to functional units (see Fig. 2).

module rec_iP(…); … rec_IP_mux_3to1_sel2_32_1 #(…) rec_IP_mux_3to1_sel2_32_1_U0( .din1( tmp_2_fu_602_p1 ),…); rec_IP_mac_muladd_8ns_8s_16s_16_1 #(…) rec_IP _mac_muladd_8ns_8s_16s_16_1_U17( .din0 (

IV. EXPERIMENTAL RESULTS

This section compares results obtained with three design flows: i) the proposed DFF one, using Vivado v2015.2 and Quartus v17.1 to synthesize the CGR DSAs; ii) Vivado HLS v2015.2; and iii) Intel FPGA SDK for OpenCL v17.0. Target devices are Xilinx Virtex 7 and Intel Cyclone V FPGAs. The test case chosen is a 1D/2D HEVC 3/5/8-tap hardware accelerator for approximate image interpolation filters, in fixed and reconfigurable configurations (with runtime filter switching) [11]. In the case of Xilinx/Intel HLS tools, a moderate effort has been put into code refactoring for optimization using shift register inference, line buffers, resource reuse when possible, and pragmas (loop unrolling and pipeline). For this reason they involve two reconfigurable designs: baseline (R) and optimized (R*). A comparison among the different flows is proposed in terms of resource utilization and early latency estimation. DFF HLS vs. Vivado IP-Level HLS: Fig. 3a shows that for standard implementations (indicated by 3/5/8/R) the DFF flow achieves better latency results. The very large latencies obtained with Vivado HLS are explained by the default areadriven synthesis (which required adding #pragma and code refactoring). Moreover, as stated in Sect. III, our flow preserves the latency values of the reconfigurable IPs, meaning that merging does not alter latency as opposed to other synthesizers and, on top of that, before sythesis estimations are equal to actual post-synthesis results. With respect to the optimized reconfigurable versions (R*), only for the 1D filter a lower use of resources (see Fig. 3b) and latency has been obtained using Vivado HLS (-72.0% register count, REG; -76.1% logic elements, LOGIC; -10.5% for minimum and 14.8% for maximum latency). In the 2D filters case our performances are superior. Latency results are more than 3 times larger in the best Vivado HLS case, and again their value is (i) not preserved and (ii) highly variable in the reconfigurable case. DFF HLS vs. OpenCL System-Level HLS: As in the Vivado HLS case, a significant effort on code refactoring is needed for optimization, which is driven by an optimization report offered at early design phases (it contains highly inaccurate resource and system-level pipeline latency/stalls estimations, rather than individual kernel latency values). Hence, there is no sane way to accurately calculate kernel latency and have insights into the generated datapath; therefore, no latency results are reported in Fig. 3a. For resource usage results refer to the kernel instantiation (See Fig. 3c). The support for the OpenCL model even at kernel level (automatic pipeline to support various threads on the fly, memory accesses optimization, replications, etc.) introduces significant resource overhead.

V. CONCLUSION

The results presented in this paper suggest that DFF HLS is a promising alternative to classical imperative HLS to build flexible and predictable CGR DSAs. Competitive resource usage are achieved with respect to commercial HLS methods, while allowing pre-synthesis and exact datapath latency predictions. By trying to ease hardware design to software developers, mainstream HLS tools have probably missed a key point in hardware design that is critical to embedded systems: having precise information on the generated datapaths to better optimize hardware accelerators through improved DSE. We demonstrated this issue on latency, proposing an alternative design flow that overcomes traditional HLS tools under this aspect. DFF HLS is able to tackle both issues: raising the abstraction level while keeping low-level performance estimates available for further hardware tuning. In this work, for the sake of brevity, we have provided the complete assessment of one single accelerator. Future works will extend the proposed analysis to other system features and more test cases.

  and L. Raffo -University of Cagliari. R. Salvador -Universidad Politécnica de Madrid. J. Sérot and M. Pelcat -the Institut Pascal. C. Rubattu, K. Desnos and M. Pelcat -INSA Rennes.

Fig. 1 .

 1 The proposed DFF HLS flow consists of three main phases: 1) Composition -Model-to-model compilation performed by MDC MDG, taking as inputs generic DFNs. Output: high-level multi-dataflow DFN of the DSA. 2) Optimization -Optimal sizing of the actor-connecting FIFOs . Optimization starts from an estimation produced by the CAPH Compiler SystemC backend, which is adapted to the multi-functional DFN case by worst case analysis. 3) Generation -Deployment of the CGR DSA. The MDC PC component outputs a top-level HDL module, corresponding to the optimized multi-functional DFN, using the CAPH generated Hardware Component Library (HCL) actors.

Fig. 1 .

 1 Fig. 1. Proposed flow: components (a); and execution sequence (b).

Fig. 3 .

 3 Fig. 3. Proposed flow vs. (a)/(b) Xilinx (XC7VX485T) and (c) Intel (5CSEMA5) target FPGAs. Intel/Xilinx resources: REG=register/FF, LOGIC=ALUT/LUT, RAM=M10K/BRAM, DSP=DSP/DSP. Data are shown on a logarithmic scale with base of 10. Latency values in clock cycles (CC) are reported in (a).

  Table I reports a qualitative comparison among our work and other frameworks available in literature for CGR DSAs.