Outline. Catapult C Design Methodology. Design Steps with Catapult 1/31/12. System-on-Chip Design Methodologies

Transcription

1 System-on-Chip Design Methodologies High-Level Synthesis using Catapult-C Olivier Sentieys IRISA/INRIA ENSSAT - Université de Rennes 1 Outline Introduction Design Flow and Tool Basics Data Types Writing C++ for Synthesis Optimizing your Design Loops Interface and Memory Synthesis EII3/M2R - 2 Catapult C Design Methodology Compatible Environments Matlab/Simulink C++ SystemC Design Steps with Catapult Algorithm design and H/S partitioning Write C code for hardware technology independent, fast simulation, compact, etc. Analyze your C code inside Catapult Constrain the micro-architecture technology, resource constraints, I/O, frequency, etc. Generate, analyze and validate hardware Gantt chart testbench generation, RTL generation EII3/M2R - 3 EII3/M2R - 4 1

2 Writing C code for Hardware: basics Big rules: No dynamic memory allocation Pointer restrictions Integer or fixed-point data types: bit accurate, no floats The style of your C code will have a great impact on design quality Add #pragma hls_design top! Use pragmas in C++ code C Design Example #define num_taps 8! Virtual WAIT #pragma hls_design top! void fir_filter (int *input,!!!!!!int coeffs[num_taps],!!!!!!int *output) {!!static int regs[num_taps];!!short temp = 0;!!for (int i = num_taps-1; i >= 0; i--) {!!!if (i == 0)!!!!regs[0] = *input;! Inputs are read!!else! with handshake!!!regs[i] = regs[i-1];!!!temp += coeffs[i] * regs[i];!!}!!*output = temp;! Outputs are registered EII3/M2R - 5 EII3/M2R - 6 Outline Introduction Design Flow and Tool Basics Data Types Writing C++ for Synthesis Optimizing your Design Loops Interface and Memory Synthesis Synthesis Flow Set working directory Add input file(s) Setup design Architectural constraints Resource constraints Schedule Generate RTL Invoke simulation EII3/M2R - 7 EII3/M2R - 8 2

3 Catapult Window Setting Up Design Invoke catapult! Load scripts Crossprobing between C code and constraints Gantt chart generated HDL reports schematic etc. EII3/M2R - 9 EII3/M2R - 10 Setting Up Design Specifying Architectural Constraints Technology: FPGA, ASIC Synthesis tool IP blocks: RAMs, pipeline multipliers Design frequency constraints Clock cycle frequency Interface One, and only one, clock ;-) je vous l avais bien dit Synchronous or asynchronous reset Enable (optional) Start and Done flags EII3/M2R - 11 EII3/M2R

4 Analysing your design Analysing your design EII3/M2R - 13 EII3/M2R - 14 Analysing your design Schematic Viewer Gantt Chart View of Data Dependencies EII3/M2R - 15 EII3/M2R

5 Schematic Viewer Outline Introduction Design Flow and Tool Basics Data Types Writing C++ for Synthesis Optimizing your Design Loops Interface and Memory Synthesis EII3/M2R - 17 EII3/M2R - 18 Data Types Type constraints signed or unsigned bit-width for integers bit-width for fixed-point types o C++ extensions: bitvectors package mc_bitvector.h int5 my_variable;! uint5 my_unsigned_variable;! SystemC Datatypes #include "systemc.h! sc_int/sc_bigint sc_int<10> tenbitint;! sc_uint/sc_biguint sc_fixed/sc_ufixed sc_fixed<20,10> a;! sc_fixed<20,10,sc_rnd,sc_sat_zero> c;! EII3/M2R - 19 EII3/M2R

6 AC Datatypes AC Datatypes #include <ac_fixed.h>! ac_int<int W, bool S> ac_int<10> tenbitint;! ac_int<10,true> tenbitintsigned;! ac_fixed<int W, int I, bool S, ac_q_mode Q, ac_o_mode O> ac_fixed<20,10,true> a;! ac_fixed<20,10,ac_rnd,ac_sat_zero> c;! EII3/M2R - 21 EII3/M2R - 22 AC Datatypes: Quantization Modes AC Datatypes: Overflow Modes EII3/M2R - 23 EII3/M2R

7 Outline Introduction Design Flow and Tool Basics Data Types Writing C++ for Synthesis Optimizing your Design Loops Interface and Memory Synthesis C++ File Format Files:.c,.cxx,.cpp or.c C++ parser C++ preprocessor #ifndef MY_HEADER_FILE_NAME! #define MY_HEADER_FILE_NAME!!code goes here...! #endif!! #pragma hls_design top! void my_design (int *input, int array[8], int *output) {!!static int temp;!!short var = *input;!!!!*output = temp;! EII3/M2R - 25 EII3/M2R - 26 Storage Types Static datatypes may only be assigned to constants during their declaration. static int a = 5; // Correct! static int b = x; // Incorrect if x is not a constant declared in the local scope! Static variables are assigned to their initial value during reset Storage types const, extern and mutable have no affect on synthesis EII3/M2R - 27 Condition Statements All branches of a conditional statement will be balanced to have the same length Every branch of a case statement should have a break Don't write code with conditional looping statements Supported: if, switch EII3/M2R - 28 switch (a) {!!case 1:!!!c = a + b;!!!break;!!case 12:!!!c = a - b;!!!break;! 7

8 Loop Statements The variable used to decide if a loop should exit should have a constant start value and increment Conditional break from a loop is preferred Each loop should have only one exit Supported: do, for, while Partial unroll of any loop EII3/M2R - 29 #pragma unroll yes // unroll a loop! #pragma unroll no // leave a loop rolled! #pragma unroll 5 // Unroll the loop 5 times! Default is to leave loops rolled Branching and Functions Branching continue statement should be avoided goto statement is not supported Supported: break continue return Functions Should have only one return statement at the end Recursive functions are not supported int my_addsub (int a, int b, bool c) {! if ( c )!!return a + b;! else!!return a - b;! EII3/M2R - 30 if ( c )!!return a + b;! return a - b;! Expressions Using Parentheses and Common Sub-Expressions Don't index arrays with signed expressions Don't use the pre- and post-increment expressions ( ++ and -- ) on a variable if that variable is used somewhere else in that expression b = 5; a = ++b * --b;! a = 6 * 5; or a = 5 * 5;! Divide / and Modulo % should be avoided Keep C integer shifts in their defined range: 0 to 31 for int, 0 to 63 for long EII3/M2R - 31 EII3/M2R

9 Multiply and Divide by Constants Constant shifts have virtually no cost in hardware Constant multiplications, divisions and modulus are converted into shifts and adds or subtracts y = a * 6;! converted into y = (a << 1) + (a << 2);! y = (int)a/2;! converted into y = ((int)a + 1) >> 1;! Loops FOR loop FOR_LOOP:for(int i=0;i<4;i++) {!!dout[i] = din[i];! } WHILE loop int i=0;! WHILE_LOOP:while(i<4){!!dout[i] = din[i];!!i++;! } EII3/M2R - 33 y = (unsigned int)a/2;! converted into y = (unsigned int) a >> 1;! DO loop EII3/M2R - 34 DO_LOOP:do{!!dout[i] = din[i];!!i++;! }while(i<4); Loops Loops Loop using one iterator Loop using multiple iterators EII3/M2R - 35 EII3/M2R

10 Conditions Conditional if Creates Dependency Chain Conditions Conditional else Splits Dependency Chain EII3/M2R - 37 EII3/M2R - 38 Outline Introduction Design Flow and Tool Basics Data Types Writing C++ for Synthesis Optimizing your Design Loops Loop Loop example int acc=0;! ACCUM:for(int i=0;i<4;i++){!!acc += din[i];! Interface and Memory Synthesis EII3/M2R - 39 EII3/M2R

11 Partial Loop Unrolling Fully Unrolled Loop int acc=0;! ACCUM:for(int i=0;i<4;i+=2){!!acc += din[i];!!acc += din[i+1];! int acc=0;! acc += din[0];! acc += din[1];! acc += din[2];! acc += din[3]; EII3/M2R - 41 EII3/M2R - 42 Loops with Conditional Bounds Loop bound is an input #include accum.h! #include<ac_int.h>! void accumulate( int din[4], int &dout,!!!!!!unsigned int ctrl){! int acc=0;! ACCUM:for(int i=0;i<ctrl;i++){!!acc += din[i];! Optimizing the Loop Control #include accum.h! #include <ac_int.h>! void accumulate(int din[4], int &dout,!!!!!!ac_int<3,false> ctrl){! int acc=0;! int i_old=0;! ACCUM:for(int i=0;i<4;i++){!!acc += din[i]; if(i_old==ctrl)!!break;!!i_old = i;! }! dout = acc;! } EII3/M2R - 43 EII3/M2R

12 Nested Loops #include accum.h! #include <ac_int.h>! #define MAX ! void accumulate(int din[2][4],!!!! int &dout){! int acc=0;! ROW:for(int i=0;i<2;i++){!!if(acc>max)!! acc = MAX;!!COL:for(int j=0;j<4;j++){!! acc += din[i][j];!!}!!dout = acc;! } Nested Loop: Unrolling the Innermost Loop ROW:for(int i=0;i<2;i++){!!acc=0;!!acc += din[i][0];!!acc += din[i][1];!!acc += din[i][2];!!acc += din[i][3];!!dout[i] = acc;! } EII3/M2R - 45 EII3/M2R - 46 Nested Loop: Unrolling the Outer Loop int acc[2];! acc[0] = 0;! COL_0: for(int j=0;j<4;j++){!!acc[0] += din[0][j];! }! dout[0] = acc[0];! acc[1] = 0;! COL_1:for(int j=0;j<4;j++){!!acc[1] += din[1][j];! }! dout[1] = acc[1]; int acc[2];! acc[0] = 0;! acc[1] = 0;! COL_0_1:for(int j=0;j<4;j++){!!acc[0] += din[0][j];! => Loop Merging!acc[1] += din[1][j];! }! dout[0] = acc[0];! dout[1] = acc[1]; But loop parallelization is complex! for(i=1; i<=n-1; i++)! for(j=1; j<=n-1; j++)!!a[i][j] = ( a[i-1][j] + a[i][j]!!!! + a[i][j-1] ) / 3.0;! Is the loop parallel? Apply the following transform t=i+j, p=j i=p-t, j=p Is it better? EII3/M2R - 47 EII3/M2R - 48 The parallel execution of DO loops, Leslie Lamport, Communications of the ACM CACM 17(2),