Project

A 16-bit virtual machine written in C with a custom assembly language and assembler written in Go.

TODO: Add address based jumping in jmp instruction

Specs

• Architecture: 16-bit
• Endianness: Little Endian
• Memory: 1 MiB (0x00000 - 0xFFFFF)
• Stack: Grows downward from top of memory
• Instruction Format: 16-bit fixed width
  • Format 1: OPCODE(4) | DST_REG(3) | SRC_REG(3) | UNUSED(6)
  • Format 2: OPCODE(4) | REG(3) | IMMEDIATE(9)

Registers

• R0-R7: General purpose (16-bit)
• PC: Program counter (20-bit)
• SP: Stack pointer (20-bit)
• FLAGS: Status flags (8-bit)
  • Zero (Z)
  • Sign (S)
  • Carry (C)
  • Overflow (O)

Assembly Syntax

Instructions follow reverse Polish notation:

<operand1> <operand2> <opcode>

Example program:

R0 5 PUT         ; Load 5 into R0
R1 10 PUT        ; Load 10 into R1
R0 R1 SUM        ; R0 = R0 + R1
R0 R1 CHECK      ; Compare R0 and R1
R2 IFZ           ; Jump to address in R2 if zero
DIE              ; Halt

Opcodes

OpCode	Equivalent	Description
DIE	HALT	Stop execution
IDLE	NOP	No operation
SET	MOV	Copy register to register
PUT	MOVI	Load immediate value
SUM	ADD	Add two registers
DIF	SUB	Subtract two registers
AND	AND	Bitwise AND
OR	OR	Bitwise OR
XOR	XOR	Bitwise XOR
CHECK	CMP	Compare (sets flags)
TELEPORT	JMP	Unconditional jump
IFZ	JZ	Jump if zero flag set
IFNZ	JNZ	Jump if zero flag clear
DEPOSIT	PUSH	Push to stack
WITHDRAW	POP	Pop from stack
EXEC	CALL	Call subroutine

Shorthand Opcodes

Single-character alternatives for compact code:

Symbol	OpCode
X	HALT
M	MOV
I	MOVI
+	ADD
-	SUB
&	AND
|	OR
^	XOR
?	CMP
@	JMP
>	PUSH
<	POP

Usage

Assemble a program:

go run assembler.go program.asm program.bin

Run the bytecode:

./vm program.bin

Building

Using Makefile -

make all -j8

Manual -

VM:

gcc -o vm main.c -std=c23 -fPIC -O3

Assembler:

cd asm_parser
go build .