FPGA学习笔记#8 Vitis HLS优化总结和案例程序的优化

本笔记使用的Vitis HLS版本为2022.2，在windows11下运行，仿真part为xcku15p_CIV-ffva1156-2LV-e，主要根据教程：跟Xilinx SAE 学HLS系列视频讲座-高亚军进行学习

学习笔记：《FPGA学习笔记》索引
FPGA学习笔记#1 HLS简介及相关概念
FPGA学习笔记#2 基本组件——CLB、SLICE、LUT、MUX、进位链、DRAM、存储单元、BRAM
FPGA学习笔记#3 Vitis HLS编程规范、数据类型、基本运算
FPGA学习笔记#4 Vitis HLS 入门的第一个工程
FPGA学习笔记#5 Vitis HLS For循环的优化（1）
FPGA学习笔记#6 Vitis HLS For循环的优化（2）
FPGA学习笔记#7 Vitis HLS 数组优化和函数优化
FPGA学习笔记#8 Vitis HLS优化总结和案例程序的优化

1.HLS优化总结

对于函数，可以使用PIPELINE或DATAFLOW。

对于循环，可以使用PIPELINE（可选rewind）、UNROLL（可选factor）或DATAFLOW。

对于数组，可以使用ARRAY_PARTITION，有block、cyclic、complete三种优化方式。

PIPELINE作用于函数和循环的情况如下，作用于循环时，两次循环之间会存在空档，被称为bubble，rewind可以解决这个问题。

对于latency，有专门的LATENCY约束用于函数和循环，可以指定min和max。

LOOP_MERGE用于合并多个循环

LOOP_FLATTEN用于perfect/semi-perfect循环

在区域中：
数据类型和位宽也是影响硬件效率和资源使用的原因
INLINE用于函数
ALLOCATION用于函数的实例化
ARRAY_MAP和ARRAY_RESHAPE用于数组
FUNCTION_INSTANTIATE用于函数

2.优化案例

2.1.案例程序

案例程序如下，请根据第四篇笔记进行项目的构建和仿真、综合、联合仿真。

Top.h：

#include <ap_int.h>
#include <ap_fixed.h>

#define WA 17
#define FA 14
#define WS 16
#define FS 14

typedef ap_fixed<WA,WA-FA> di_t;
typedef ap_fixed<WS,WS-FS> do_t;
typedef ap_uint<2> flag_t;

const do_t Kn = 0.607252935;
const di_t PI = 3.1415926;

void cir_cordic (di_t full_alpha, do_t &out_sin, do_t &out_cos);

Top.cpp：

#include "top.h"
 
void pre_cir_cordic (di_t full_alpha, di_t &alpha, flag_t &flag)
{
    if (full_alpha > PI/2)
    {
        alpha = PI - full_alpha;
        flag = 2;
    }
    else if (full_alpha < -PI/2)
    {
        alpha = -PI - full_alpha;
        flag = 3;
    }
    else
    {
        alpha = full_alpha;
        flag = 0;
    }
}

void cir_cordic_calculate (di_t alpha, flag_t flag, do_t &mysin, do_t &mycos, flag_t &flag_delay)
{
    const int N = 16;
    do_t xi[N];
    do_t yi[N];
    di_t zi[N];
flag_t flag_delay_a[N];

    xi[0] = Kn;
    yi[0] = 0;
    zi[0] = alpha;
flag_delay_a[0] = flag;

    const di_t myarctan[16] = {
        0.7853981633974483, 
        0.4636476090008061, 
        0.24497866312686414, 
        0.12435499454676144, 
        0.06241880999595735, 
        0.031239833430268277, 
        0.015623728620476831, 
        0.007812341060101111, 
        0.0039062301319669718, 
        0.0019531225164788188, 
        0.0009765621895593195, 
        0.0004882812111948983, 
        0.00024414062014936177, 
        0.00012207031189367021, 
        6.103515617420877e-05, 
        3.0517578115526096e-05
    };
    int m = 0;
loop:
    for (m = 0; m < N; m++)
    {
        if (zi[m] >= 0)
        {
            xi[m+1] = xi[m] - (yi[m] >> m);
            yi[m+1] = yi[m] + (xi[m] >> m);
            zi[m+1] = zi[m] - myarctan[m];
        }
        else
        {
            xi[m+1] = xi[m] + (yi[m] >> m);
            yi[m+1] = yi[m] - (xi[m] >> m);
            zi[m+1] = zi[m] + myarctan[m];
        }
        flag_delay_a[m+1] = flag_delay_a[m];
    }
    mysin = yi[N-1];
    mycos = xi[N-1];
    flag_delay = flag_delay_a[N-1];
}

void post_cir_cordic (do_t mysin, do_t mycos, flag_t flag_delay, do_t &sin_out, do_t &cos_out)
{
    switch(int(flag_delay))
    {
        case 2: sin_out = mysin; cos_out = -mycos; break;
        case 3: sin_out = -mysin; cos_out = -mycos; break;
        default: sin_out = mysin; cos_out = mycos; break;
    }
}

void cir_cordic (di_t full_alpha, do_t &out_sin, do_t &out_cos)
{
    di_t alpha;
    flag_t flag;
    do_t mysin;
    do_t mycos;
flag_t flag_delay;

    pre_cir_cordic(full_alpha, alpha, flag);
    cir_cordic_calculate(alpha, flag, mysin, mycos, flag_delay);
    post_cir_cordic(mysin, mycos, flag_delay, out_sin, out_cos);
}

Test.cpp：

#include <iostream>
#include <iomanip>
#include <cmath>
#include <math.h>
#include "top.h"

using namespace std;

int main(){
    const int N = 13;
    di_t alpha[N] = {
        3.01837,
        3.02838,
        3.03839,
        3.0484,
        3.05835,
        3.06836,
        3.07837,
        3.08838,
        3.09839,
        3.1084,
        3.11835,
        3.12836,
        3.13837
    };
    do_t sinRef[N] = {
        0.122864,
        0.112915,
        0.102966,
        0.0930176,
        0.0830688,
        0.0730591,
        0.0631104,
        0.0531006,
        0.0431519,
        0.0331421,
        0.0231323,
        0.0131836,
        0.00317383
    };
    do_t cosRef[N] = {
        -0.992432,
        -0.993652,
        -0.99469,
        -0.995667,
        -0.996582,
        -0.997375,
        -0.998047,
        -0.998596,
        -0.999084,
        -0.999451,
        -0.999756,
        -0.999939,
        -1.0
    };
    do_t sinres[N] = {0};
    do_t cosres[N] = {0};
    int ErrCntSin = 0;
    int ErrCntCos = 0;
    float precision = pow(2, -10);
int i;

    for (i = 0; i < N; i++)
    {
        cir_cordic(alpha[i], sinres[i], cosres[i]);
}

    cout << setfill('-') << setw(90) << "-" << endl;
    cout << setfill(' ') << setw(18) << right << "Alpha";
    cout << setfill(' ') << setw(18) << right << "sin";
    cout << setfill(' ') << setw(18) << right << "sinRef";
    cout << setfill(' ') << setw(18) << right << "cos";
    cout << setfill(' ') << setw(18) << right << "cosRef" << endl;
cout << setfill('-') << setw(90) << "-" << endl;

    for (i = 0; i < N; i++)
    {
        cout << setfill(' ') << setw(18) << right << alpha[i];
        cout << setfill(' ') << setw(18) << right << sinres[i];
        cout << setfill(' ') << setw(18) << right << sinRef[i];
        cout << setfill(' ') << setw(18) << right << cosres[i];
        cout << setfill(' ') << setw(18) << right << cosRef[i];

        if (abs(float(sinres[i] - sinRef[i])) > precision)
        {
            ErrCntSin++;
            cout << setfill(' ') << setw(18) << right << "(sin failed)";
        }
        if (abs(float(cosres[i] - cosRef[i])) > precision)
        {
            ErrCntCos++;
            cout << setfill(' ') << setw(18) << right << "(cos failed)";
        }
        cout << endl;
}

cout << setfill('-') << setw(90) << "-" << endl;

    if (ErrCntSin + ErrCntCos == 0)
    {
        cout << "Test passed!" << endl;
        return 0;
    }
    else
    {
        cout << "Test failed!" << endl;
        cout << "sin failed: " << ErrCntSin << endl;
        cout << "cos failed: " << ErrCntCos << endl;
        return 1;
    }
}