V22.0436 - Prof. Grishman

Assignment 5:   MIPS ALU

In this assignment you will use Logisim to build the MIPS ALU, including all of the inputs and outputs shown in figure B.5.12 except for the Overflow output.  There will be two 32-bit inputs, A and B;  two 1-bit inputs, Ainvert and Bnegate;  and a 2-bit input, Operation.  There will be one 32-bit output, Result, and one 1-bit output, Zero.

Rather than build a 1-bit ALU and then combine 32 of them, you will probably find it easier to build the ALU directly from 32-bit-wide components.  By setting the "bit width" attribute to 32 for the AND gate, you get in effect 32 AND gates.  Similarly you can create a 32-bit-wide OR gate, inverter, multiplexers, and adder (the adder is part of the arithmetic library).

Most of the wires will therefore be 32-bit bundles.  The only instances where you have to split out individual wires involve the slt logic (where you have to get the high bit of the adder output and connect it to the low bit of a multiplexer input) and the zero logic (where you have to OR together all 32 wires).  You may find it easier to first build the zero logic (a 32-input NOR gate) as a separate sub-circuit which has one input (a 32-bit bundle) and one output (zero).

Due Wednesday, November 1st.

Mail your homework (the .circ file) to  grishman@cs.nyu.edu and to mgp255@nyu.edu (Ms. Merim Puthuparampil) and mark the mail CompArch -- Asgn 5.