MIPS Virtual Machine

A small experiment to learn more about MIPS. This repo includes a a virtual machine/mips simulator, an assembler and a REPL-style tool.

You can load and assemble a file by running

$ machine program.asm

...or directly load a memory file

$ machine memory.mem

The implementation is loosely based on the MIPS Architecture for Programmers Volume II-A: The MIPS32 Instruction Set Manual. However, there is close to no test coverage so expect a lot of things to be broken.

Memory layout

The memory is 4096 bytes large by default.

Address	Description
0x7fff	Stack base address
0x4000	Heap base address
0x3000	Data base address
0x2FFC	Terminal output address
0x0000	Text (source code) base address

When creating a new machine $sp will point to the stack base address and $gp will point to the data base address. Use the .data and .text assembly directives to place your program data in the right place. The program will start at the label "main" if there is one, otherwise it will start at the text base address.

Output

If you wish to print something to the terminal. You can put an address to a zero terminated string at 0x2ffc..0x2fff in the memory and it will be outputed to your stdout.

A simple print procedure could be implemented like this:

        .data
msg:    .asciiz "Hello world!"

        .text 
main:
        la $t0, msg     # Load a pointer to the string in $t0 
        li $t1, 0x2FFC  # Load the address of the output in $t1
        sw $t0, 0($t1)  # Store the pointer to the string at 
                        # the addr of the output.

Assembly language

Directives

The following directives are supported:

ascii
asciiz
byte
data
globl (however, it does nothing)
half
space
text
word
TODO: align

Instruction

The following instruction are all implemented (although, definitely not tested).

add rd, rs, rt
addi rt, rs, imm
addiu rt, rs, imm
addu rd, rs, rt
and rd, rs, rt
andi rt, rs, imm
beq rs, rt, offset
bne rs, rt, offset
bgtz rs, label
div rd, rs, rt
mod rd, rs, rt
divu rd, rs, rt
modu rd, rs, rt
j label
jal label
jalr rd, rs
jr rs
lb rt, offset(base)
lbu rt, offset(base)
lhu rt, offset(base)
lui rt, imm
lw rt, offset(base)
nor rd, rs, rt
xor rd, rs, rt
or rd, rs, rt
ori rt, rs, imm
sb rt offset(base)
sh rt offset(base)
slt rd, rs, rt
slti rt, rs, imm
sltiu rt, rs, imm
sltu rd, rs, rt
sll rd, rt, sa
srl rd, rt, sa
sra rd, rt, sa
sub rd, rs, rt
subu rd, rs, rt
sw rt, offset(base)
li li rs, imm (pseudo instruction)
la la rs, label (pseudo instruction)

adelhult / mips-machine