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【计算机系统要素】使用D触发器实现寄存器、内存和计数器D触发器寄存器内存计数器

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我是靠谱客的博主 鲜艳蚂蚁，最近开发中收集的这篇文章主要介绍【计算机系统要素】使用D触发器实现寄存器、内存和计数器D触发器寄存器内存计数器，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

本文是笔者拜读《计算机系统要素》第3章（时序逻辑）的实践项目。
本文的HDL程序所调用的组合逻辑模块来自前几篇博客。

目录

  • D触发器
  • 寄存器
    • 1比特位寄存器
    • 多比特位寄存器
  • 内存
    • 8字内存
    • 64字内存
    • 512字内存
    • 4K字内存
    • 16K字内存
  • 计数器

D触发器

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DFF的输出被赋予了上个时钟周期的输入，所有的DFF门都连接同一个主时钟，所有时序芯片都在主时钟频率的协调下共同工作。

和Nand门一样，DFF门在计算机体系中处于非常底层的位置，计算机中的所有时序芯片（寄存器、内存、计数器）都基于大量的DFF门。

DFF的物理实现是个复杂的任务，它使用反馈电路（仅基于Nand门）连接几个基本的逻辑门。

寄存器

1比特位寄存器

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如果希望寄存器开始存储一个新值，可以把这个值置于in输入口，然后将load位设为1；如果希望寄存器一直存储它的内部值直到新的指令到来，就将load设置为0。
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CHIP Bit {
    IN in, load; // t
    OUT out; // t+1

    PARTS:
    // Put your code here:
    Mux(a = o1, b = in, sel = load, out = o2);
    DFF(in = o2, out = out);
    DFF(in = o2, out = o1);
}

内部接线o1的默认初值是false，即低电平。
输入是t时刻的，输出是t+1时刻的，该输出又是t+2时刻输出的一部分。

多比特位寄存器

在这里插入图片描述
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在这里插入图片描述
读：要读取寄存器的内容，只需获取它的输出。
写：要将新数据d写入寄存器，只需将d置于in输入管脚，并将load输入管脚的值设为1，这样，在下一个时钟周期，寄存器被赋予新的数据值，输出变成了d。

CHIP Register {
    IN in[16], load;
    OUT out[16];

    PARTS:
    // Put your code here:
    Bit(in = in[0], load = load, out = out[0]);
    Bit(in = in[1], load = load, out = out[1]);
    Bit(in = in[2], load = load, out = out[2]);
    Bit(in = in[3], load = load, out = out[3]);
    Bit(in = in[4], load = load, out = out[4]);
    Bit(in = in[5], load = load, out = out[5]);
    Bit(in = in[6], load = load, out = out[6]);
    Bit(in = in[7], load = load, out = out[7]);
    Bit(in = in[8], load = load, out = out[8]);
    Bit(in = in[9], load = load, out = out[9]);
    Bit(in = in[10], load = load, out = out[10]);
    Bit(in = in[11], load = load, out = out[11]);
    Bit(in = in[12], load = load, out = out[12]);
    Bit(in = in[13], load = load, out = out[13]);
    Bit(in = in[14], load = load, out = out[14]);
    Bit(in = in[15], load = load, out = out[15]);
}

一个寄存器的大小就是一个字的宽度。

内存

在这里插入图片描述
随机访问存储器（RAM），是由n（表示内存尺寸）个w（表示内存宽度）位寄存器组成的阵列。
在这里插入图片描述
在这里插入图片描述

k是地址总线的个数。

读：要读取编号为m的寄存器，我们先将m置于address输入管脚。RAM的直接存取逻辑将选中编号为m的寄存器，于是该寄存器将它的输出发送到RAM的输出管脚，这是个不涉及时间的组合逻辑操作。

写：要将新的数据值d写入编号为m的寄存器，我们同样将m置于address输入管脚，并将d置于in管脚，然后确认load为1。这样使得RAM的直接存取逻辑去选中m号寄存器，load位来使能写操作，在下一个时钟周期里，被选中的寄存器将会被赋予新的数据值d，RAM的输出值也变成了d。

8字内存

CHIP RAM8 {
    IN in[16], load, address[3];
    OUT out[16];

    PARTS:
    // Put your code here:
    DMux8Way(in = true, sel = address, a = ram0, b = ram1, c = ram2, d = ram3, e = ram4, f = ram5, g = ram6, h = ram7);
    // 寻址，写/读数据
    // 每个寄存器要么将数据置为in，要么维持原值不变
    And(a = ram0, b = load, out = s0);
    Register(in = in, load = s0, out = o0);
    And(a = ram1, b = load, out = s1);
    Register(in = in, load = s1, out = o1);
    And(a = ram2, b = load, out = s2);
    Register(in = in, load = s2, out = o2);
    And(a = ram3, b = load, out = s3);
    Register(in = in, load = s3, out = o3);
    And(a = ram4, b = load, out = s4);
    Register(in = in, load = s4, out = o4);
    And(a = ram5, b = load, out = s5);
    Register(in = in, load = s5, out = o5);
    And(a = ram6, b = load, out = s6);
    Register(in = in, load = s6, out = o6);
    And(a = ram7, b = load, out = s7);
    Register(in = in, load = s7, out = o7);
    // 通过八选一选择器，输出数据
    Mux8Way16(a = o0, b = o1, c = o2, d = o3, e = o4, f = o5, g = o6, h = o7, sel = address, out = out);
}

仅当某个寄存器被选中且load为1，才改变该寄存器的值。
在时序逻辑中，需要经过一定的时钟周期数才能使输入流到输出；而在组合逻辑中，输入一瞬间就能流到输出。

64字内存

CHIP RAM64 {
    IN in[16], load, address[6];
    OUT out[16];

    PARTS:
    // Put your code here:
    DMux8Way(in = true, sel = address[3..5], a = ram0, b = ram1, c = ram2, d = ram3, e = ram4, f = ram5, g = ram6, h = ram7);
    And(a = ram0, b = load, out = s0);
    RAM8(in = in, load = s0, address = address[0..2], out = o0);
    And(a = ram1, b = load, out = s1);
    RAM8(in = in, load = s1, address = address[0..2], out = o1);
    And(a = ram2, b = load, out = s2);
    RAM8(in = in, load = s2, address = address[0..2], out = o2);
    And(a = ram3, b = load, out = s3);
    RAM8(in = in, load = s3, address = address[0..2], out = o3);
    And(a = ram4, b = load, out = s4);
    RAM8(in = in, load = s4, address = address[0..2], out = o4);
    And(a = ram5, b = load, out = s5);
    RAM8(in = in, load = s5, address = address[0..2], out = o5);
    And(a = ram6, b = load, out = s6);
    RAM8(in = in, load = s6, address = address[0..2], out = o6);
    And(a = ram7, b = load, out = s7);
    RAM8(in = in, load = s7, address = address[0..2], out = o7);

    Mux8Way16(a = o0, b = o1, c = o2, d = o3, e = o4, f = o5, g = o6, h = o7, sel = address[3..5], out = out);
}

高3位寻址芯片，低3位在芯片里寻址字。

512字内存

CHIP RAM512 {
    IN in[16], load, address[9];
    OUT out[16];

    PARTS:
    // Put your code here:
    DMux8Way(in = true, sel = address[6..8], a = ram0, b = ram1, c = ram2, d = ram3, e = ram4, f = ram5, g = ram6, h = ram7);
    And(a = ram0, b = load, out = s0);
    RAM64(in = in, load = s0, address = address[0..5], out = o0);
    And(a = ram1, b = load, out = s1);
    RAM64(in = in, load = s1, address = address[0..5], out = o1);
    And(a = ram2, b = load, out = s2);
    RAM64(in = in, load = s2, address = address[0..5], out = o2);
    And(a = ram3, b = load, out = s3);
    RAM64(in = in, load = s3, address = address[0..5], out = o3);
    And(a = ram4, b = load, out = s4);
    RAM64(in = in, load = s4, address = address[0..5], out = o4);
    And(a = ram5, b = load, out = s5);
    RAM64(in = in, load = s5, address = address[0..5], out = o5);
    And(a = ram6, b = load, out = s6);
    RAM64(in = in, load = s6, address = address[0..5], out = o6);
    And(a = ram7, b = load, out = s7);
    RAM64(in = in, load = s7, address = address[0..5], out = o7);

    Mux8Way16(a = o0, b = o1, c = o2, d = o3, e = o4, f = o5, g = o6, h = o7, sel = address[6..8], out = out);
}

4K字内存

CHIP RAM4K {
    IN in[16], load, address[12];
    OUT out[16];

    PARTS:
    // Put your code here:
    DMux8Way(in = true, sel = address[9..11], a = ram0, b = ram1, c = ram2, d = ram3, e = ram4, f = ram5, g = ram6, h = ram7);
    And(a = ram0, b = load, out = s0);
    RAM512(in = in, load = s0, address = address[0..8], out = o0);
    And(a = ram1, b = load, out = s1);
    RAM512(in = in, load = s1, address = address[0..8], out = o1);
    And(a = ram2, b = load, out = s2);
    RAM512(in = in, load = s2, address = address[0..8], out = o2);
    And(a = ram3, b = load, out = s3);
    RAM512(in = in, load = s3, address = address[0..8], out = o3);
    And(a = ram4, b = load, out = s4);
    RAM512(in = in, load = s4, address = address[0..8], out = o4);
    And(a = ram5, b = load, out = s5);
    RAM512(in = in, load = s5, address = address[0..8], out = o5);
    And(a = ram6, b = load, out = s6);
    RAM512(in = in, load = s6, address = address[0..8], out = o6);
    And(a = ram7, b = load, out = s7);
    RAM512(in = in, load = s7, address = address[0..8], out = o7);

    Mux8Way16(a = o0, b = o1, c = o2, d = o3, e = o4, f = o5, g = o6, h = o7, sel = address[9..11], out = out);
}

16K字内存

CHIP RAM16K {
    IN in[16], load, address[14];
    OUT out[16];

    PARTS:
    // Put your code here:
    DMux4Way(in = true, sel = address[12..13], a = ram0, b = ram1, c = ram2, d = ram3);
    
    And(a = ram0, b = load, out = s0);
    RAM4K(in = in, load = s0, address = address[0..11], out = o0);
    And(a = ram1, b = load, out = s1);
    RAM4K(in = in, load = s1, address = address[0..11], out = o1);
    And(a = ram2, b = load, out = s2);
    RAM4K(in = in, load = s2, address = address[0..11], out = o2);
    And(a = ram3, b = load, out = s3);
    RAM4K(in = in, load = s3, address = address[0..11], out = o3);

    Mux4Way16(a = o0, b = o1, c = o2, d = o3, sel = address[12..13], out = out);
}

计数器

指令地址计数器：内容是计算机下一时钟周期要读取和执行的指令地址。大多数情况下，计数器在每个时钟周期内做简单的加1操作，其它情况下要进行跳转，甚至置0（重新执行程序）。

我们需要一个可重载、可重置的计数器。

当inc=1时，计数器在每个时钟周期自加，输出值out(t)=out(t-1)+1；如果想要将计数器重置为0，就将reset置为1；如果想要将其初始化为某个计数值d，就将d置于in输入管脚然后将load位置1。
在这里插入图片描述
在这里插入图片描述

CHIP PC {
    IN in[16],load,inc,reset;
    OUT out[16];

    PARTS:
    // Put your code here:
    Xor16(a = in, b = in, out = reseto); //reset输出
    Inc16(in = ot, out = inco); // inc输出
    
    Mux16(a = in, b = reseto, sel = reset, out = o1);
    Or(a = reset, b = load, out = or1);
    Mux16(a = inco, b = o1, sel = or1, out = o2);

    Or(a = or1, b = inc, out = or2);
    Register(in = o2, load = or2, out = out);
    Register(in = o2, load = or2, out = ot);
}

注意load、inc和reset的优先级不一样。

最后

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