Microprogramming

The lab asks you to interpret some microprograms and then write write your own simple microprograms.

Resources: Throughout this lab, you will need to consult Figures 4-1, 4-2, 4-5, 4-6, and 4-7 (section 4.2) in Tanenbaum's text.

Collaboration: As with the work for the previous labs, the following steps are to be done on paper collaboratively. Everyone should work in a group of two (preferred) or three students; within a group, each person should take responsibility for leading discussion for some of the problems.

Steps for this Lab: In the following, assume the Local Variable register LV contains the base address of the integer array X.

1. Consider Microprogram 1 which implements the Pascal statement X[2] := X[1] - X[0] .
   This code may be printed with the command:

   dvips ~walker/public_html/courses/211.fa99/labs/micro-code-1.dvi
   

   1. Write a sentence or two to explain why each statement does what is claimed by the comment field (or correct any mistakes in the code, explaining what was wrong and how the correction fixes the problem).

   2. Why do you think the address of X[1] was stored both in the MAR and OPC?

   3. Why do you think the address of X[1] was stored in OPC rather than in LV?
      (Hint: what might be the long-term use of LV?)

   4. Explain how timings effect what data are available where at each step.

   5. While this code is finished with instruction 4, explain why the bus may not be used for the next job until another clock cycle is finished.

2. Write a microprogram to computer X[2] := X[0] - X[1] .

   Annotate each step of your microprogram to explain what the line does. Compare the complexity of this program with that the first version?

3. Write microcode for the Pascal statement

   X[1] := 8*X[0] - 17;
   

   Again, annotate each step of your microprogram

Work to be turned in:

• Write out your comments for step 1.

• Write out the microcode for steps 2 and 3 using a microcode form for each.
  This form may be printed with the command:

  dvips ~walker/public_html/courses/211.fa99/labs/micro-code-form.dvi
  

  For each instruction, be sure to place a 0 or 1 in each field. You may assume that your microprogram will be stored in consecutive memory locations of the micro-memory, beginning in location 0.

This document is available on the World Wide Web as

     http://www.math.grin.edu/~walker/courses/211.fa99/labs/lab.microprogramming.html