Question

我正在尝试设计一个流水线cpu模拟器。代码相当复杂，至少对我而言。有多个头文件和源文件。代码编译。

运行时，它在第一次迭代（时钟周期）中运行良好。但迭代并非如此。在花了几个小时找到错误之后，我发现了什么是错的，但不知道为什么。以下功能：

MemoryAccess(ir, pc, ground, '0', instrMem);

在instrMem中的索引“pc”处获取指令并将其存储在“ir”中。以下是函数中变量的声明：

typedef char bit32[33];
bit8 instrMem[4096];    /* instruction memory */
bit32 pc, ir, ground;

问题是从第二次迭代开始，“ir”的值仍为“00000000”。我检查了instrMem，值不是全0。我还使用驱动程序函数检查了MemoryAccess（）的工作情况。它工作正常。

我无法理解为什么它适用于第一次迭代，而不是从那时起。

有人可以帮忙。有没有办法找出问题所在？

以下是main（）函数的相关部分：

   for(cycle=0; ; cycle++) 
{
    /* load IR with PC value */
    printf("I am at the beginning of the cycle loop");
    MemoryAccess(ir, pc, ground, '0', instrMem); 

    /* report fetched register values */
    printf("cycle: %d, PC: %.32s (%d), IR: %.32s\n\t", cycle, pc, bit32toint(pc), ir);

    /* halt check */
    if (bit32toint(ir) == 0x0000003F) {
        printf("\nmachine halted\n");
        break;
    }

    /* PC + 4 data path */
    RCAdder_32(pcPlus4, ground, pc, "00000000000000000000000000000100", '0');

    /* jump data path */
    shiftleftby2(jumpAddress, ir);
    jumpAddress[0] = pcPlus4[0];
    jumpAddress[1] = pcPlus4[1];
    jumpAddress[2] = pcPlus4[2];
    jumpAddress[3] = pcPlus4[3];

    /* sign extended / shifted immediate data path */
    signextend(immSignExt, &ir[16]); 
    shiftleftby2(immShifted, immSignExt); 

    /* control unit data path */
    ControlUnit(ir, &ir[26], &regWrite, &regDest,
                    &memRead, &memWrite, &memToReg, 
                    &jump, &branch, &aluSrc, aluOp);

    /* register memory data path - read */
    Mux2_5(regWriteAddr, &ir[11], &ir[16], regDest);
    registerAccess(&regOut1, &regOut2, &ir[6], &ir[11], regWriteAddr, regIn, '0');

    /* alu data path */
    Mux2_32(aluSrcVal, regOut2, immSignExt, aluSrc);
    zero = ALU(&aluOut, regOut1, aluSrcVal, aluOp);

    /* branch data path */
    RCAdder_32(branchAddress, ground, pcPlus4, immShifted, '0');
    Mux2_32(mbranchAddress, pcPlus4, branchAddress, AND2_1(zero, branch));
    Mux2_32(pc, mbranchAddress, jumpAddress, jump);

    /* main memory data path */
    MemoryAccess(memOut, aluOut, regOut2, memWrite, mainMem);
    Mux2_32(regIn, aluOut, memOut, memToReg);

    /* register memory data path - write */
    registerAccess(&regOut1, &regOut2, &ir[6], &ir[11], regWriteAddr, regIn, regWrite);

    /* dump register memory and signal information */
    for (i=0; i < 14; i++) {
        inttobitn(i, 5, tmp);
        registerAccess(&regOut1, &regOut2, tmp, &ir[11], regWriteAddr, regIn, '0');
        printf("R%d: %d, ", i, bit32toint(regOut1));
    }
    printf("\b\b\n\tbranchAddress = %.32s (%d) jumpAddress = %.32s (%d)\n",
        branchAddress, bit32toint(branchAddress), jumpAddress, bit32toint(jumpAddress));
    printf("\topcode = %.6s, immSignExt = %.32s (%d), immShifted = %.32s (%d), PC+4 = %.32s (%d)\n",
        ir, immSignExt, bit32toint(immSignExt), immShifted, bit32toint(immShifted), pcPlus4, bit32toint(pcPlus4));
    printf("\tregWrite = %c, regDest = %c, memRead = %c, memWrite = %c, memToReg = %c, jump = %c, branch = %c, aluSrc = %c, aluOp = %.3s, zero = %c\n",
        regWrite, regDest, memRead, memWrite, memToReg, jump, branch, aluSrc, aluOp, zero);
    getchar();
}

以下是MemoryAccess（）函数：

void MemoryAccess(bit32 read_out, bit32 addr, bit32 write_in, signal write_enable, bit8 memory[4096]){

int address= bitntoint(12, addr);
setbit8(read_out, memory[address]);
setbit8(&read_out[8], memory[address+1]);
setbit8(&read_out[16], memory[address+2]);
setbit8(&read_out[24], memory[address+3]);

if (write_enable){
    setbit8(memory[address], write_in);
    setbit8(memory[address+1], &write_in[8]);
    setbit8(memory[address+2], &write_in[16]);
    setbit8(memory[address+3], &write_in[24]);
}

}

Setbit8（a，b）将b复制到a并附加'\ 0'。

Answer 1

渴望发表评论：

1显示的代码似乎没有增加pc。

2虽然您将'0'作为writabel标记传递，但未按预期使用。您可能想要更改

if (write_enable)

是

if (write_enable && ('0' != (*write_enable)))

由于前一个版本memory被作为第三个参数（write_in）传入的指针所引用的内容覆盖，可能是0 s。

C：仅在第一次迭代中起作用的函数

1 个答案: