V22.0436 - Prof. Grishman

Lecture 12: MIPS Processor Design: Single Cycle Control

A simulator for the single-cycle MIPS machine, PathSim, is available from St. Bonaventure University.
(A older version which runs under earlier versions of Java is available here.)

Building the Control Unit

We then have to convert these two truth tables to combinational logic.  P&H do this in Appendix D, section 2.  For the main control unit, we use standard sum-of-products logic.  The full truth table, with opcode inputs and control signal outputs, is shown in Figure 4.22.  The resulting circuit is shown in Figure D.2.5.  For the ALU control unit, we take advantage of the don't cares in the truth table to produce a simple circuit, shown in Figure D.2.3.

Combining these circuits with the data path produces a complete computer (Figure 4.17).

How the single cycle CPU works (pages 321-326)

Sequence reflects data flow ... everything happens in a single clock cycle.

for all instructions: fetch instruction from instruction memory

for R-type instructions:

for load: for store: for beq: