dsnair / cpu-emulator

Learn how CPU works at the low level

Computer Architecture

Project

• Implement the LS-8 Emulator

Task List: add this to the first comment of your Pull Request

Day 1: Get print8.ls8 running

• Inventory what is here
• Implement the CPU constructor
• Add RAM functions ram_read() and ram_write()
• Implement the core of run()
• Implement the HLT instruction handler
• Add the LDI instruction
• Add the PRN instruction

Day 2: Add the ability to load files dynamically, get mult.ls8 running

• Un-hardcode the machine code
• Implement the load() function to load an .ls8 file given the filename passed in as an argument
• Implement a Multiply instruction (run mult8.ls8)

Day 3: Stack

• Implement the System Stack and be able to run the stack.ls8 program

Day 4: Get call.ls8 running

• Implement the CALL and RET instructions
• Implement Subroutine Calls and be able to run the call.ls8 program

Day 5: Sprint Challenge, get sctest.ls8 working

• Add the CMP instruction and equal flag to your LS-8.
• Add the JMP instruction.
• Add the JEQ and JNE instructions.

1. When is the ALU activated in the CPU?

   ALU is activated when logic based arithmetic operations are called.

2. Why is the purpose of a CPU stack?

   1. Temporary storage of variables. Suppose we want to store the values of some variables. Since there are a limited number of registers, we can push their values on to a stack, re-use those registers to store those variable values, then pop them off the stack when done.

   2. Store the return address of a subroutine. Suppose CALL is called. The program executes that part of the code until RET is reached. At RET, the program resumes to what it was doing before CALL. We can store this return address in the CPU stack.

   3. Store registers and CPU state to handle interrupt. When there is an interrupt, like a keyboard interrupt, that part of the program runs. After the interrupt ends and the program is to be resumed, we can restore the entire CPU state such as registers, flags, etc. from the CPU stack.

   4. Store subroutine local variables. Same as #1

3. Convert 01010110 to Decimal:

   0101 = (0 * 2^3) + (1 * 2^2) + (0 * 2^1) + (1 * 2^0) = 5

   0110 = (0 * 2^3) + (1 * 2^2) + (1 * 2^1) + (0 * 2^0) = 6

   Thus, 56

4. Convert 10100011 to Hexadecimal:

   1010 = (1 * 2^3) + (0 * 2^2) + (1 * 2^1) + (0 * 2^0) = 10 = A

   0011 = (0 * 2^3) + (0 * 2^2) + (1 * 2^1) + (1 * 2^0) = 3

   Thus, A3

Stretch

• Add the ALU operations: AND OR XOR NOT SHL SHR MOD
• Add an ADDI extension instruction to add an immediate value to a register
• Add timer interrupts
• Add keyboard interrupts
• Write an LS-8 assembly program to draw a curved histogram on the screen