CSC262 CPU/Opcode Playground

This simulated CPU has a single register, "current" and supports a very small number of instructions. Since it is so simple, it provides the ability to experiment.

There is no binary format to the instructions; only a simplified text format. Memory is available: 1024 32-bit int slots.

Here's a python implementation via Google Colab.

Executable factorial(5) program

This is what works with the current system:

# the input
load 5 
# save it to locations 0 (fact) and 1 (n)
store @1
store @0

# n --
load @1
sub 1
store @1

# if zero, go to done
goto-rel 3 ifz

# fact *= n;
mul @0
store @0

# go back to n--
goto-abs 3

# load the computed factorial
load @0

Consider a nicer text version of this program: this is what we would like to work.

  # take a value as input
  prompt
  store n
  store fact

loop:

  # n -= 1
  load n
  sub 1
  store n

  # if (n == 0) finished! 
  goto done ifz

  # fact *= n
  mul fact
  store fact

  goto loop

done:
  # load the computed value to the "current" register
  load fact
  print

Making better-factorial possible:

(30) Create an input/output device for this CPU.

1. Create the "prompt" instruction.
   1. Create an Opcode for Prompt.
   2. Support converting the "prompt" to an Opcode.
   3. Implement it in the CPU-switch statement.
      1. Add a Scanner around System.in as a field to CPUSim, call nextInt?
      2. Read a number from the user, after some kind of generic prompt.
2. Create a "print" instruction, following similar steps.

(20) Load the higher-level language bits:

• Construct a class ASMLine similar to Instruction that has its own parse method (arguments can now be strings!).

(20) Variable Numbering

• Loop through this program, collecting all unique variables mentioned.
• Assign these variables numeric identifiers.
• Output raw assembly.

(20) Label Numbering

• Convert your ASMLine labels to not be part of the instruction sequence, but owned by whatever instruction follows them.
• You'll need a way to mark labels on your ASMLine class.
• Convert the higher-level "goto" statement to either "goto-rel" or "goto-abs" lower-level commands.

(10) Experience

• Support directly converting ASMLine programs to Instruction programs so that they can be run directly.