Reconfigurable Computing

1. Reconfigurable Computing Ender YILMAZ, Hasan Tahsin OĞUZ Reconfigurable Computing

2. Overview • Energy savings are in average 35% to 70%, and speedup is in average 3 to 7 times. • Reduction in size and component • Time to market • Flexibility and upgradability Reconfigurable Computing

3. Three ways of supporting processing requirements • High performance microprocessors • Even expensive μPs are not fast enough for many applications • Power consumption(100W or more) • Not convenient for embedded applications • Application specific ICs (ASICs) • Provides a natural mechanism for large amount of parellalism • Does not suffer from serial instruction fetch • Consumes less power than reconfigurable devices • Not general purpose • Time to market • Infeasable for many embedded systems, only high volume of production makes it feasible Reconfigurable Computing

4. Three ways of supporing processing requirements(continued) • Reconfigurable Computing • In the middle of μP and ASICs as performance and power consumption • Parellalism due to hardware implementation • Cheaper for low volume production • Design time and time to market is much less • Functional units can change over time • General Purpose Reconfigurable Computing

5. System Level Architectures Five classes of reconfigurable systems a External stand-alone processing unit b Attached processing unit c Co-processor d Reconfigurable functional unit e Processor embedded in a reconfigurable fabric Reconfigurable Computing

6. System Level Architectures Reconfigurable Computing

7. Reconfigurable Fabric • consists of reconfigurable functional units, reconfigurable interconnect and a flexible interface to the rest of the system • There is a tradeoff between flexibility and efficiency. Reconfigurable Computing

8. Functional Units • Fine Grained: implements functions for single or small number of bits • Coarse Grained: larger, ALU, DSP Reconfigurable Computing

9. Emerging Directions • Low power techniques • Activity reduction in power-aware design tools • Leakage current reduction • Dual supply voltage methods • Asynchronous architectures • Fine grained asynchronous pipelines • Quasi delay insensitive architectures • Globally async. Locally sync. • Molecular microelectronics • Promising for increasing capacity and performance of reconf. Comp. Arch. Reconfigurable Computing

10. Main Trends in Architectures • Coarse grained fabrics • Cost of interconnection is increasing due to advancements in tech., granularity of LU’s are increasing to reduce routing overhead • Heterogeneous functions • Due to migration to more advanced tech., number of transistors devoted to the reconf. logic increases. Multipliers , DSP units can be added • Soft cores • Instructions are programmable • Although being less area and speed efficient, flexible Reconfigurable Computing

11. Design Methods • Hardware compilers for high-level descriptions are key to reduce the productivity gap for advanced circuit development • Design methods can be generally categorized into two; general design methods and special design methods • General purpose designs • Annotation and constraint driven approach • Source-directed compilation approach • Special purpose design • Digital Signal Processing • The word-length optimisation • Other Design Methods • Run time customisation • Soft instruction processor • Multi FPGA compilation Reconfigurable Computing

12. General Purpose Design • Design methods and tools are based on general purpose programming languages such as C, C++ and Java • HDLs: VHDL and Verilog are also available • A number of compilers from C to hardware have been developed • Target hardware or hardware/software • Two different approached • Annotation and constraint driven approach • Annotations are used in source-code + constraint files • Only minor changes are needed to produce a compilable program from software description • Source-directed compilation approach • Source languages are adopted to enable explicit description of parellelism, communication and other customisable hardware resources Reconfigurable Computing

13. Summary of General Purpose Hardware Compilers Reconfigurable Computing

14. Special Purpose Design • There are many specific problem domains which deserve special consideration • Exploiting domain specific properties: • Describe the computation (MATLAB-Simulink) • Optimise the implementation • Digital Signal Processing • The word-length optimisation Reconfigurable Computing

15. Digital Signal Processing • One of the most successful applications for reconfigurable computing is real-time digital signal processing(DSP) • Inclusion of hardware support for DSP in FPGA • DSP problems share similar properties • Algorithms are numerically insensitive but have very simple control structures • Controlled numerical error is acceptable • SNR exist for measuring numeric precision • Design is performed in Simulink • Designer need not deal with low level implementation issues Reconfigurable Computing

16. The word-length optimisation • Unlike mP based implementations size of each variable is customisable. • Numerical accuracy, design size, speed and power cons. • Most important decision is selection of an appropriate word-length and scaling for each signal • The accuracy is less sensitive to some variables than to others • Considering error and area information, it is possible to achieve a highly efficient DSP implementation • Word-length optimisation problem is NP-hard • Heuristics are used, area/signal quality tradeoff • Analytic methods are faster but pessimistic Reconfigurable Computing

17. Other Design Methods • Run-time customisation • Soft instruction processors • Multi-FPGA compilation Reconfigurable Computing

18. Run-time customisation • One part of the system continues to be operational, while other part is being reconfigured • At compile time, an initial configuration bitstream and incremental bitstreams have to be produced • Runtime design optimisation techniques • Runtime constraint propagation, producing a smaller circuit with higher performance by boolean algebra optimisation • Library compilation, precompiled modules are loaded into reconfigurable resources by procedure call mechanisms • Exploiting information about program branch probabilities • Promote utilization by dedicating more resources the branches which execute more frequently • Hardware compiler produces a collection of designs, each optimised for a particular branch probability, best one is selected at runtime Reconfigurable Computing

19. Soft Instruction Processor • Two examples of soft instruction processors are MizroBlaze and Nios • Customisation of resources and instructions is supported • Time for instruction fetch and decode is reduced, each custom instruction replaces several regular instructions • Additional resources can be assigned to a custom instruction to improve the performance Reconfigurable Computing

20. Multi-FPGA Compilation • Compiler can generate designs using speculative and lazy execution to improve the performance • A single program is partitioned between host and reconfigurable resources Reconfigurable Computing

21. Dynamic Instruction Set Computer Reconfigurable Computing

22. DISC-Example Code Reconfigurable Computing

23. DISC-Example Application Reconfigurable Computing