1 Advanced VLSI Course Class Presentation An Asynchronous Array of Simple Processors for DSP Applications Rasoul Yousefi Electrical and Computer Engineering Department University of Tehran

2 Copyright Slides used –Zhiyi Yu, Michael Meeuwsen, Ryan Apperson, Omar Sattari, Michael Lai, Jeremy Webb, Eric Work, Tinoosh Mohsenin, Mandeep Singh, Bevan Baas “An Asynchronous Array of Simple rocessors for DSP Applications”, VLSI Computation Lab, ECE Department,University of California, Davis, USA,2006 IEEE International Solid-State Circuits Conference

3 Outline The idea Project objectives Key features of the AsAP processor Design of the AsAP processor Results Trends

4 The idea Using simple processor cores with small instruction and data memory to dramatically reduce area and power while increasing performance [1]

5 Outline The idea Project objectives Key features of the AsAP processor Design of the AsAP processor Results Trends

6 Project Objectives Programming flexibility Increasing performance Reducing power Reducing area Suitable for future fabrication technologies Performance & Energy efficiency Programming flexibility ASIC FPGA Prog. DSP AsAP Performance, Area, Power improvement !!! [1]

7 Outline The idea Project objectives Key features of the AsAP processor Design of the AsAP processor Results Trends

8 Key Features of the AsAP Processor Chip multiprocessor High performance Small memory & simple processor High energy efficiency Globally asynchronous locally synchronous (GALS) Technology scalability Nearest neighbor communication

9 High Performance Through Chip Multiprocessor Increasing the clock frequency is challenging Parallelism is more promising –Instruction level parallelism (VLIW, Superscalar) –Data level parallelism (SIMD) –Task level parallelism Higher clock frequency Increased design complexity & lower energy efficiency Deeper pipeline

10 Task Level Parallelism Well suited for DSP applications scram coding inter- leave mod. map loadfft inter- leave IFFT win- dow up- samp filter scale clip up- samp filter in out training pilots a/g wireless LAN (54 Mbps, 5 GHz) baseband transmit path Task1 Task2 Task3 A B C Memory Task1Task2 A B C Proc. Proc.1 Proc.2 Task3 Proc.3 Improves performance and potentially reduces memory size … Widely available in many DSP applications … … [1]

11 Memory Size in Modern Processors Memory occupies much of the area in modern processors — this reduces area available for the core and consumes large amounts of power Memories frequently contain the critical path Area and energy dissipation can be dramatically decreased while speed can be increased with smaller memories Area breakdown other mem core TI_C64x Itanium SPARC BlGe/L [ISSCC 02, 05] [from1]

12 Can we use small memory ?

13 Small Memory Requirements for DSP Tasks The memory required for common DSP tasks is quite small Several hundred words of memory are sufficient for many DSP tasks TaskIMem (words) DMem (words) N-pt FIR 6 2N 8-pt DCT x8 2-D DCT Conv. coding (k = 7) Huffman encode N-pt convolution 29 2N 64-pt complex FFT Bubble sort 20 1 N merge sort 50 N Square root Exponential [1]

14 A system with many processors can use individual processors or groups of processors to compute individual tasks and intermediate data can be transmitted between processors with a small memory requirement So it is possible to use small memory

15 GALS Clocking Style The challenge of globally synchronous systems –Design difficulty when using high clock frequencies, long clock wires caused by large chip sizes, and large circuit parameter variations –High clock power consumption and lack of flexibility to independently control clock frequencies How about totally asynchronous design style –Lack of EDA tool support –Design complexity and circuit overhead The GALS compromise –Synchronous blocks each operating in their own independent clock domain

16 The GALS architecture basics Power breakdown in a high-performance CPU[2] Datapath Memory Control I/O Clock [Adopted from 2]

17 The GALS architecture basics Eliminating global clock  Eliminating a major source of power consumption[2] Frequency of each SB can be tailored to the local needs  Reducing average frequency and overall power consumption[2] SB1 SB2 SB3 Data Handshake protocol [Adopted from 2]

18 On Chip Communication Methods to avoid global wires –Network on chip (NOC) –Local communication –Nearest neighbor communication nearest local [1]

19 Outline The idea Project objectives Key features of the AsAP processor Design of the AsAP processor Results Trends

20 AsAP Block Diagram GALS array of identical processors –Each processor is a reduced complexity programmable DSP with small memories –Each processor can receive data from any two neighbors and send data to any of its four neighbors [1]

21 IFetch PC Inst. Mem Decode Mem. Read Src Select EXE 1EXE 2EXE 3 Result Select Write Back FIFO 0 RD FIFO 1 RD Data Mem Read DC Mem Read De- code Addr. Gens. ALU Data Mem Write DC Mem Write Proc Output Single Processor Architecture bit instructions 9-stage pipeline Bypass Multiply Accumulator × ACCACC + [1]

22 reset halt clk Programmable Clock Oscillator Standard cell based Configurable frequency –Delay tunable stages using 7 parallel tri-state inverters –1 to 128 clock divider Results –1.66 MHz – 702 MHz –Max gap: 0.08 MHz (1.66 – 500 MHz) ………… … … … … stage_sel... Clock divider [1]

23 Write side Read side east west south Write logic FIFO 0 Read logic east north west south CPUCPU FIFO 1 Processor east north west south Inter-processor Communication Each processor contains two dual-clock FIFOs Rd/Wr in separate clock domains north Binary Gray & Sync. addr SRAM [1]

24 Advantages of the AsAP Clocking System Simplified clock tree design –The maximum span is < 1 mm in 0.18 µm Scalable – easy to add processors Improved energy efficiency –Clock halts in 9 cycles (processor dissipates leakage power only) and restores in < 1 cycle according to work availability –53% and 65% power saving –Independent clock and voltage scaling (individual processor voltage scaling not implemented in this version)

25 Physical Design 0.18 µm TSMC Standard cell Design flow –Completely synthesized, except oscillator –Macro memory blocks used for four main memories –Completely auto placed and routed To simplify physical design, clock gating not implemented in this version

26 Transistors: 1 Proc 230,000 Chip 8.5 million Max speed: V Area: 1 Proc 0.66 mm² Chip 32.1 mm² Power (1 1.8V, 475 MHz): Typical application 32 mW Typical 100% active 84 mW Worst case 144 mW Power (1 0.9V, 116 MHz): Typical application 2.4 mW Single Processor OSC FIFOs DMem IMem 810 µm 5.65 mm 810 µm 5.68 mm Chip Micrograph of the 6 x 6 Array [1]

27 Outline The idea Project objectives Key features of the AsAP processor Design of the AsAP processor Results Trends

28 Area Evaluation Most of AsAP’s area is for the core (66%) Each processor requires a very small area; more than 20x smaller than others Area breakdown comm mem core Processor area (mm ² ) 20x All scaled to 0.13 µm [ISSCC 05, 00; ISCA04; CMPON96] TI RAW Fujitsu BlGe/ AsAP C64x 4-VLIW L TI CELL/ Fujitsu RAW ARM AsAP C64x SPE 4-VLIW [1]

29 Power and Performance Power / Clock frequency / Scale * (mW/MHz) Peak performance density (MOPS/mm²) All scaled to 0.13 µm * Assume 2 ops/cycle for CELL/SPE and 3.3 ops/cycle for TI C64x Note: word widths and workload not factored [ISSCC 05, 00; ISCA04; CMPON96] Higher performance ÷ area, and Lower estimated energy [1]

30 Pad Scram Conv. Code Punc Inter- leave 1 Inter- leave 2 Mod. Map Pilot Insert Train IFFT BR IFFT Mem IFFT BF IFFT Output GI/ Wind. GI/ Wind. IFFT Mem IFFT BF FIR IFFT BF IFFT Mem Output Sync IFFT Data bits To D/A converter a/802.11g Wireless Transmitter Implementation 22 processors Fully functional on chip MHz 30% of 54 Mb/s Code unscheduled and lightly optimized ~10x performance and 35x – 75x lower energy dissipation than 8-way VLIW TI C62x [SIPS 04; ICC 02] [1]

31 Summary Scalable programmable processing array –Many processors on a single chip –Reduced complexity processors with small memories –GALS clocking style –Nearest neighbor communication Results –0.18 µm, V 32 mW application power 84 mW 100% active power 2.4 mW application 116 MHz and 0.9 V –High performance density: 475 MOPS in 0.66 mm² –Well suited for future fabrication technologies

32 Trends Clock Gating Dynamic voltage scaling but adds level- conversion for asynchronous communication interface[3] CAD tool –CAD tools for asynchronous design is mature, but not commercially strong yet.[3]

33 References 1. Zhiyi Yu, Michael Meeuwsen, Ryan Apperson, Omar Sattari, Michael Lai, Jeremy Webb, Eric Work, Tinoosh Mohsenin, Mandeep Singh, Bevan Baas, “ An Asynchronous Array of Simple rocessors for DSP Applications ”, VLSI Computation Lab, ECE Department, University of California, Davis, USA,2006 IEEE International Solid-State Circuits Conference 2. A.Hemani, T.Meincke, S.Kumar, A.Postula, T.olsson, P.Nilsson, J.Oberg, P.Ellervee,D.Lundqvist, “ Lowering power consumption in clock by using Globally Asynchronous Locally Synchronous design style” 3. Anoop Iyer,Diana Marculescu, “Power and Performance Evaluation of Globally Asynchronous Locally Synchronous Processors”, Proceedings of the 29th Annual International Symposium on Computer Architecture (ISCA.02)

34 Question? Thanks for your attention