CSE30321 Computer Architecture I
Lab 5: Expanding an ISA and Coding in Assembly (50 points)
Assigned: Week of October 29th. Due: Week of November 5th
1 Introduction
Looking back to big pictures objectives of class, the purpose of this lab is to:
•Begin to see how the fundamental components of a modern microprocessor work together.
•Give you expertise in comparing and contrasting different computer architectures. A hardware implementa-
tion of the 6-instruction processor would be different from a hardware implementation of the MIPS datapath
discussed in class. Memory is accessed in different ways, MIPS provides more instruction types ... which
implies a more complex datapath, etc. These issues will all ultimately impact the time required to execute
code written in a high-level language – as well as how it is executed.
2 Insight into Self Modifying Code
Background:
•Secs. 2 and 3 of the lab are designed to show you how the 6-instruction processor instruction set architecture
can be used to execute more complex high-level language code – even with a limited number of instructions
and a relatively simple datapath. In Sec. 2, we’ll first see how more complex code can be executed with just
6-instruction. In Sec. 3 we’ll quantitatively compare 6-instruction code to an equivalent MIPS version.
What do I do?
1. Open ISE and create a new project called “lab5” in an empty directory. Download and extract the zipped
Verilog files from the course web page into a different directory. In ISE, add the Verilog files by clicking “Add
Copy of Source...” under the ”Project” menu.
Note: This version of the processor is slightly different from the one in the previous labs. See Appendix for
more details about this processor design.
2. Download the file ArrayAccess.s from the course web page. Convert the assembly code to machine code. We
have provided a new assembly/simulator for the 6-instruction processor to aid this process. (The Java-based
simulator does not work with self-modifying code. See the course web site for instructions on how to use the
Linux-based assembler/simulator.)
3. Put the machine code in the memory by modifying “comb mem.v” (values are in hexadecimal).
4. Simulate the code such that the loops are executed three times. The output ”R0 out” can be disregarded until
later in the lab.
5. Whenever you observe changes in the register file and memory, record the time when this happens (i.e.,
during the execution of which instruction), the register and/or memory location, as well as the corresponding
contents before and after the change.
Questions:
•(A) What does the sixth instruction try to achieve?
•(B) Based on your observations, describe what this code snippet accomplishes.
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