Comparison Between a Digital Processor

Transcription

1 A Platform-Based Comparison Between a Digital Signal Processor and a General-Purpose Processor from an Perspective 1, 1 Ole Olsen, 1 Peter Koch 2 Allan Federiksen, 3 Ole Wolf, 4 Rasmus Damsgaard Christiansen 1,,, 9220 Aalborg, Denmark, {kapokasa,oo,pk}@kom.auc.dk 2 Nokia Danmark A/S, Allan.Frederiksen@nokia.com 3 DSP Assist, wolf@dspassist.com 4 ETI A/S, rasmus@christiansen.dk (kapokasa@cpk.auc.dk),, Center for PersonKommunikation,

2 Contents Introduction Scenario Platforms Case Studies Results Conclusions Future Work Center for PersonKommunikation,

3 Introduction Platforms state-of of-the-art processors well suited for modern DSP applications. processors with DSP extensions. Motivation What would it happen if C was the only programming language available? Previous Work: A. Frederiksen,, R. Christiansen, J. Bier, and P. Koch. An Evaluation of Compiler-Processor Interaction for DSP Applications. BDTI. EEMBC ( Microprocessor Benchmarking Consortium). (kapokasa@cpk.auc.dk),, Center for PersonKommunikation,

4 Scenario Platform Comparison. Case Studies Analysis C Programs C55x ARM9E-S Platform Analysis Measurements Cycle Count Code Size Profiling Profiling Cycle Count Code Size / Evaluation Improvement Factors (kapokasa@cpk.auc.dk),, Center for PersonKommunikation,

5 Contents Introduction Scenario Platforms Summary of Architectures TMS320C55x ARM9E-S Case Studies Results Conclusions Future Work Center for PersonKommunikation,

6 Summary of architectures Feature/Platform C55x ARM9 Instructions/cycle up to 2 1 Numeric Representations Fixed-point Fixed-point Wordlength Intended Applications 16 applications that are DSP intensive 32 mixture of µ-controller and DSP performance Pipeline 7 stages 5 stages Register File Small and heterogeneous Large and homogeneous Instruction Set CISC RISC (ARM & Thumb) Orthogonality No Instruction length Variable (8-48 bits) Fixed (32 or 16 bits) Viterbi Support No MAC Dual MAC No Circular Buffering No Zero Overhead Looping Conditional Execution No Saturated Arithmetic (kapokasa@cpk.auc.dk),, Center for PersonKommunikation,

7 TMS320C55x Data Path C Bus D Bus B Bus (Coefficient) MAC-1 MAC-2 Shifter 40-Bit ALU 16-Bit ALU AC0 AC1 AC2 AC3 Three Address Generators DR0 DR1 C Y X DR2 DR3 Data Computation Unit (D unit) Address Data Flow Unit (A unit) AR0 AR1 AR2 AR3 AR4 AR5 AR6 AR7 CDP 5 Address Buses 24-bit (kapokasa@cpk.auc.dk),, Center for PersonKommunikation, Source: BDTI

8 ARM9 Data Path RDATA MAC 32-Bit ALU Shifter Register Bank Plus Program Counter WDATA ADDRESS Center for PersonKommunikation,

9 Contents Introduction Scenario Platforms Case Studies Characterization Code Types Program Size Description Results Conclusions Future Work Center for PersonKommunikation,

10 Characterization of Case Studies Case Study Type Size Matrix Functions DSP Kernel Dhrystone CVSD Control DSP Kernel Application Viterbi Control Kernel Domain Considered TYPE Control Grey Zone DSP HLL Kernel Application SIZE Center for PersonKommunikation,

11 Code Types Control Code Origin: Finite State Machines (FSM). Properties: Branch intensive.. Contains Switch / if-then then-else else constructs, many basic blocks. Control code is typically size-constrained rather than time- constrained. DSP Code Origin: mathematical transformations used in signal processing. Properties: inner loops, performing arithmetic intensive functions, i.e., a high instruction locality. The time-constrained parts of a DSP application are often DSP code. Grey zone Code In general, everything in between Control and DSP code. The term grey zone code is used about DSP code, which is not time-critical. I.e., functions with DSP code that are rarely executed. (kapokasa@cpk.auc.dk),, Center for PersonKommunikation,

12 Program Size HLL constructs: pointer addressing, function call, loop constructs Too small for relevant results. Kernels: FFT, FIR, LMS, small state machines Applications: CVSD, GSM EFR transcoder. Provide a realistic mixture of different code types. (kapokasa@cpk.auc.dk),, Center for PersonKommunikation,

13 Case Studies Description Examples from real life applications to synthetic benchmarks. Matrix Functions Autocorrelation Matrix.. (AC) Forward Substitution Vector. (FS) Dhrystone Mark (DM) Synthetic Benchmark,, by Reinhold P. Weicker. Version 2.1 released in Tries to reflect systems programming practice at that time. CVSD (Continuous Variable Slope Delta Modulation) (CE / CD) Used on the Bluetooth air interface. More robust than log PCM (Pulse Code Modulation). Encoding / decoding of a 64 ksamples/s signal. Viterbi (VD) Andrea Viterbi in Recover bit errors in sequences. It finds the most probable sequence of symbols from all the transitions in a state diagram. (kapokasa@cpk.auc.dk),, Center for PersonKommunikation,

14 Contents Introduction Scenario Platforms Case Studies Results C55x - ARM Comparison Cycle Count Code Size ARM Thumb Comparison Conclusions Future Work (kapokasa@cpk.auc.dk),, Center for PersonKommunikation,

15 C55x - ARM Comparison (Cycle Count) C55x supports complex addressing generation and parallel data transfer. ARM is a micro-controller controller showing best performance in control. C55x ARM9E-S Cycle Count Improvement factor % A C F S D M C E C D V D Experiment (kapokasa@cpk.auc.dk),, Center for PersonKommunikation,

16 C55x - ARM Comparison (Code Size) C55x supports variable length instruction word. CISC processors have an advantage over RISC. C55x ARM9E-S Code Size Improvement factor % A C F S D M C E C D V D Experiment (kapokasa@cpk.auc.dk),, Center for PersonKommunikation,

17 ARM Thumb Instruction Set Comparison (I) Thumb is a subset of ARM: Cycle count -> ~ 85% increase in cycle count Code Size -> ~ 25% reduction in code size Cycle Count Increase Code Size Decrease Percentage % Auto Forward Dhrystone CVSD CVSD Decode Viterbi Correlation Substitution Mark Encode Function Decoding Matrix Vector Function Experiment (kapokasa@cpk.auc.dk),, Center for PersonKommunikation,

18 ARM Thumb Instruction Set Comparison (II) Extensible to C55x: CS 25% ~ 20% CC 85% ~ 17% ARM Thumb ARM Thumb Cycle Count % Code Size % Original 90/10 80/20 70/30 60/40 50/50 Original 90/10 80/20 70/30 60/40 50/50 Partition Partition Percentage % CC CS Original 90/10 80/20 70/30 60/40 50/50 Partition (kapokasa@cpk.auc.dk),, Center for PersonKommunikation,

19 Conclusions Platform approach is relevant if C language should be the programming language. Compilers considered are not able to exploit advanced architectural features. Standard C extensions for DSP features (intrinsics( intrinsics) ) would be desirable. ARM9 compares favorably with C55x for the experiments performed. Thumb instruction set improves code density at the cost of an increase in cycle count. General purpose processors with DSP extensions are a viable alternative to DSP processors. (kapokasa@cpk.auc.dk),, Center for PersonKommunikation,

20 Future Work Apply GSM EFR to the ARM platform. Extend experiments to ADI s Blackfin Power Efficiency measurements and comparisons of the platforms. Students and Ph.D s are welcome. (kapokasa@cpk.auc.dk),, Center for PersonKommunikation,