Principles of Computer Organization
Fall Semester, 1997
Department of Computer Science
The purpose of this lab is to give you a chance to explore
microprogramming and how the microprogram interacts with the
hardware to implement a conventional machine language interpreter.
We will be using a Macintosh program called µArchitecture
Simulator, by Fabrizio Oddone, which provides
a simulated hardware machine very similar to the Mic-1 machine
described in Tanenbaum. It allows you to view and modify
the conventional memory, to modify the microcode running on the
simulated hardware, to "see" the signals flowing through the
circuits of the hardware, and step through the microcode at the
clock sub-cycle level.
Such simulators are used in the development of real microcode, and
this lab is designed to give you a feel for what it is like to
write (and debug) true machine language.
Using the Mic-1 control store which I have entered (but not thoroughly
tested), do each of the following and demonstrate it for your neighbor:
Enter an instruction at address 2000(hex) in conventional memory.
Use the Mac-1 instruction set (Fig. 4-14 on page 185) and pick an
instruction that interests you. Clear the registers and step through
the microcode by clock sub-cycle and watch carefully to see what's
happening both in the hardware animation window, and in the microcode
window. Does the instruction do exactly what you expected? Is it correct?
Pick 8 sequential lines from the microprogram. Examine them
carefully to see if they are identical (in description) to the
corresponding lines in the text (Fig. 4-16, page 190-191). Now,
check to see if each of them exacly implements the correct hardware
functions. Note that Oddone has eliminated the TIR register (I have
used A), and I have assumed that the X12 and Low8 registers
have been pre-loaded with the AMASK and SMASK constants (0FFF and 00FF,
Delete a microcode instruction that you have tested, and add an
empty one in its place. Now, modify the empty instruction to
re-implement what you deleted. Test by re-running the test you
Write a small program using a few (4-10) instructions that you know work.
Step through the microcode to verify that your program works.
Think of a new Mac-1 instruction that you'd like to add. For example,
AND8 which does an 8-bit AND with the value in the accumulator and the
8-bit operand of the instruction. Now, replace one of the existing
instructions with your new microcode. You may need to jump
to 79 and add microinstructions to the end of the code if the
new instruction takes more microinstructions than the original instruction.
Test your new instruction.
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