X16 CPU and Assembler

This is a small project I started working on about a year ago, just to be able to run some small programs and write an assembler. The assembler is written in Python to make it super fast to write and extend, while the virtual machine is fully written in C for performance.

To assemble a demo, you can run the following commands:

python3 asm.py demos/hello/helloworld.dS # or any other demo!
./vm --prog demos/hello/helloworld.bin

To debug, use the --debug or the --step-delay flags, or see the --help switch for a list of the available commands!

Registers

x0, x1, x2, x3 — general purpose registers

sp — stack pointer

bp — base pointer (start of the program)

pc — program counter. current location in program.

Syscalls

0x00 — stop execution

0x01 — print first byte of x0 register as character

0x02 — toggle step debug (register dump on every step)

0x03 — load file from disk

Input:

• x0 — memory address to load into
• x1 — pointer to path of the file

Instructions

pushi [imm] — push an immediate value to the stack. always 16 bit

push [reg] — push a register to the stack. always 16 bit

pop [reg] — pop a value off the stack into a register

addi [imm] [reg] — add an immediate value to a register

add [reg] [reg] — add a register to a register

sys [imm8] — send a syscall to the cpu

cmp [reg] [reg] — compare two register values

cmpi [imm] [reg] — compare the value of a register to an immediate value

not [reg] — bitwise negate a register

andi [imm] [reg] — bitwise AND a register with an immediate value

ori [imm] [reg] — bitwise OR a register with an immediate value

b [label] — immediately branch to a label

blt [label] — branch to a label if a comparison result is a negative number

bgt [label] — branch to a label if a comparison result is a positive number

be [label] — branch to a label if a comparison result is zero

bne [label] — branch to a label if a comparison result is non-zero

Directives

.str [string] — encode data into the executable

Macros

{# [macro_name] [number of arguments]
    ; instructions here ...

    ;[instruction] #[index of argument]
    ; push #0
    ; or
    ; pop #1
#}

for example,

; exchange the values between two registers
{# xchg 2
    push #0
    mov #1, #0
    pop #1
#}

would be used like:

xchg x1, x2

and would result in the code generated as

push x1
mov x2, x1
pop x2