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https://github.com/soconnor0919/eceg431.git
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Sean O'Connor
b0c57a8a7e
- Removed invalid finalout internal bus - Use out[0..7], out[8..15], out[15] directly for flag computation - Fixes HDL sub-bus restriction error
76 lines
2.4 KiB
Plaintext
76 lines
2.4 KiB
Plaintext
// This file is part of www.nand2tetris.org
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// and the book "The Elements of Computing Systems"
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// by Nisan and Schocken, MIT Press.
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// File name: projects/2/ALU.hdl
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/**
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* ALU (Arithmetic Logic Unit):
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* Computes out = one of the following functions:
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* 0, 1, -1,
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* x, y, !x, !y, -x, -y,
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* x + 1, y + 1, x - 1, y - 1,
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* x + y, x - y, y - x,
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* x & y, x | y
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* on the 16-bit inputs x, y,
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* according to the input bits zx, nx, zy, ny, f, no.
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* In addition, computes the two output bits:
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* if (out == 0) zr = 1, else zr = 0
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* if (out < 0) ng = 1, else ng = 0
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*/
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// Implementation: Manipulates the x and y inputs
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// and operates on the resulting values, as follows:
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// if (zx == 1) sets x = 0 // 16-bit constant
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// if (nx == 1) sets x = !x // bitwise not
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// if (zy == 1) sets y = 0 // 16-bit constant
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// if (ny == 1) sets y = !y // bitwise not
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// if (f == 1) sets out = x + y // integer 2's complement addition
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// if (f == 0) sets out = x & y // bitwise and
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// if (no == 1) sets out = !out // bitwise not
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CHIP ALU {
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IN
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x[16], y[16], // 16-bit inputs
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zx, // zero the x input?
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nx, // negate the x input?
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zy, // zero the y input?
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ny, // negate the y input?
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f, // compute (out = x + y) or (out = x & y)?
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no; // negate the out output?
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OUT
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out[16], // 16-bit output
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zr, // if (out == 0) equals 1, else 0
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ng; // if (out < 0) equals 1, else 0
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PARTS:
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// handle zx (zero x)
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Mux16(a=x, b=false, sel=zx, out=x1);
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// handle nx (negate x)
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Not16(in=x1, out=notx1);
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Mux16(a=x1, b=notx1, sel=nx, out=x2);
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// handle zy (zero y)
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Mux16(a=y, b=false, sel=zy, out=y1);
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// handle ny (negate y)
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Not16(in=y1, out=noty1);
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Mux16(a=y1, b=noty1, sel=ny, out=y2);
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// handle f (add or and)
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Add16(a=x2, b=y2, out=addout);
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And16(a=x2, b=y2, out=andout);
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Mux16(a=andout, b=addout, sel=f, out=fout);
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// handle no (negate out)
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Not16(in=fout, out=notfout);
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Mux16(a=fout, b=notfout, sel=no, out=out);
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// compute zr (zero flag)
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Or8Way(in=out[0..7], out=tmp1);
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Or8Way(in=out[8..15], out=tmp2);
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Or(a=tmp1, b=tmp2, out=notzr);
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Not(in=notzr, out=zr);
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// compute ng (negative flag)
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And(a=out[15], b=true, out=ng);
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}
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