Pre-requisites

• how to turn assembly language statements into machine language statements (you did this for Lab 7), and
• how the single-cycle CPU shown in Figure 7.24 works.

Instructions

For this lab, you going to complete the single-cycle CPU discussed in Chapter 7 of the Harris and Harris textbook. You will need to

1. Add the missing connections to StarterCPU.jls for j, sw, and lw.
2. Complete the CPU's microcode. (Use starterMicrocode as a sample.)
3. Add jal and jr to your CPU.
4. Modify the CPU so that unsigned and logical operations have their immediate values zero-extended instead of sign-extended.
5. Determine the optimal clock period.

Your complete CPU should support these instructions:

Microcode

Use starterMicrocode as a sample and starting point.

Other Instructions

Hints

• The built-in Register file simulates negative-edge triggered flip-flops. Your registers (e.g., the program counter) should also use negative-edge triggered flip flops. When using negative-edge triggered flip-flops, the clock's falling edge defines the beginning of each CPU cycle.
• The WE, OE, and CS inputs to RAM and ROM are active low.
• Even though the RAM and ROM control inputs are active low, none of the Control wires are active low. Specifically, the memWrite and memRead wires are 1 when a memory write or memory read is desired.
• The built-in RAM and ROM circuits are word addressable, whereas the memories in the textbook are byte addressable. Make sure your circuit converts between them correctly. (The Instruction Memory circuit I provide takes bytes as input, not words.)
• Read carefully about how MIPS implements jump and branch. In particular, notice (1) how MIPS fills bits 28-32 of the jump target and (2) that the branch offset is added to PC + 4, not PC.
• JLS's un-bundle feature puts the low-order bits at the top. This is different from the diagrams in the book. Read carefully.
• Make use of probes, watches, and displays to help debug your circuit.

Testing

• basicOpsDemoTest.a
• basicLoadStoreTest.a
• Multiply.a

Running tests by hand

To debug your CPU, you may want to run test programs by hand. The Instruction Memory I provided is configured to load instructions from a file named instructions. You will want to maintain several different test programs. Make sure these programs are not namedinstructions, and simply copy (not move) the program you want to test to instructions. Once you have copied the file, JLS will automatically load instruction memory with the desired program. (The file instructions must be in the current working directory. This is the directory from which you launched JLS. Be careful when launching JLS from an icon because it may not be obvious which directory is the current working directory.)

Similarly, make sure your microcode is in a file named singleCycleMicrocode and that the file is located in the current working directory (i.e., the directory from which you launch JLS).

The JLSCircuitTester suite contains marsAssembler, a program that will take assembly files as input and generate MIPS code formatted for use as aninstructions file: The file contains two columns. The first is the word address of the instruction in hex, and the second is the MIPS binary instruction in hex. Currently marsAssembler writes only to the standard output. Use file redirection to save the output to a file.

To examine the results of your program, place a watch on any registers of interest and the RAM unit for Main Memory. When simulating the CPU, I like to set the "Step" value equal to the clock period.

Submission and grading

This assignment will be worth 50 points, divided as follows:

Penalties

• You will loose 3 points for each buggy submission (-5 if the submission contains too few tests).

Note: It may not be possible to effectively test some instructions if others are broken. For example, it is not possible to test lw without first using an I-type instruction to load the base register. The list above reflects my testing order. If it is not possible to easily test instruction y because instruction x is broken, you will receive 0 points for instruction y. Thus, if your I-type instructions are broken, you will likely receive a 0 for the assignment.

Add a text box to your jls files that includes

• your names,
• the file name,
• the assignment name, and
• the assignment due date.

When you are convinced your CPU works, e-mail me both your CPU and microcode files.

Note:

• You are encouraged to consult with other groups when designing your test programs.
• You are also encouraged to test your CPU using programs written by other groups.

Updated Sunday, 4 November 2018, 8:12 PM