16-bit Virtual Machine

16-bit Virtual Machine written in C.

Prerequisites

• A C compiler (e.g., GCC)

Optional

• Make — Required for building via the Makefile.
• SDL2 — Required for building the vm-sdl frontend.
• Python 3.10+ — Required for running the assembler in asm/.

Build

With Make

$ make

Without Make

$ cc vm/vm.c -c -o vm/vm.o
$ cc vm/vm.o frontend/dbg.c -o vm-dbg
$ cc vm/vm.o frontend/tty.c -o vm-tty
$ cc vm/vm.o frontend/sdl.c -o vm-sdl $(sdl2-config --cflags --libs)

Usage

VM

$ <desired-frontend> <desired-ROM>

Assembler

$ asm/assembler.py --help

Project Structure

• asm/ — Contains an assembler implementation.
• examples/ — Contains ROM files and their corresponding source code, which can be assembled using the assembler in asm/.
• frontend/ — Contains C sources for the VM frontend.
• vm/ — Contains C sources for the VM backend.

Details

Registers

Register	Description
IP	Instruction pointer
SP	Stack pointer
BP	Base pointer
AC	Accumulator
R1	General purpose
R2	General purpose
R3	General purpose
R4	General purpose
R5	General purpose
R6	General purpose
R7	General purpose
R8	General purpose

Operations

Operand notations

Notation	Description
I	Immediate value
R	Register
IM	Immediate memory (address)
RM	Register memory (address)

Operation table

Code	Instruction	Operands	Description
0x00	NOP	-	Performs no operation
0x01	MOV_R_I	R1, I1	Move 16 bits from I1 to R1
0x02	MOV_R_R	R1, R2	Move 16 bits from R2 to R1
0x03	MOV_R_IM	R1, IM1	Move 16 bits from IM1 to R1
0x04	MOV_R_RM	R1, RM1	Move 16 bits from RM1 to R1
0x05	MOV_IM_I	IM1, I1	Move 16 bits from I1 to IM1
0x06	MOV_IM_R	IM1, R1	Move 16 bits from R1 to IM1
0x07	MOV_IM_IM	IM1, IM2	Move 16 bits from IM2 to IM1
0x08	MOV_IM_RM	IM1, RM1	Move 16 bits from RM1 to IM1
0x09	MOV_RM_I	RM1, I1	Move 16 bits from I1 to RM1
0x0a	MOV_RM_R	RM1, R1	Move 16 bits from R1 to RM1
0x0b	MOV_RM_IM	RM1, IM1	Move 16 bits from IM1 to RM1
0x0c	MOV_RM_RM	RM1, RM2	Move 16 bits from RM2 to RM2
0x0d	MOVB_R_I	R1, I1	Move 8 bits from I1 to R1
0x0e	MOVB_R_R	R1, R2	Move 8 bits from R2 to R1
0x0f	MOVB_R_IM	R1, IM1	Move 8 bits from IM1 to R1
0x10	MOVB_R_RM	R1, RM1	Move 8 bits from RM1 to R1
0x11	MOVB_IM_I	IM1, I1	Move 8 bits from I1 to IM1
0x12	MOVB_IM_R	IM1, R1	Move 8 bits from R1 to IM1
0x13	MOVB_IM_IM	IM1, IM2	Move 8 bits from IM2 to IM1
0x14	MOVB_IM_RM	IM1, RM1	Move 8 bits from RM1 to IM1
0x15	MOVB_RM_I	RM1, I1	Move 8 bits from I1 to RM1
0x16	MOVB_RM_R	RM1, R1	Move 8 bits from R1 to RM1
0x17	MOVB_RM_IM	RM1, IM1	Move 8 bits from IM1 to RM1
0x18	MOVB_RM_RM	RM1, RM2	Move 8 bits from RM2 to RM2
0x19	PUSH_I	I1	Push I1 to stack
0x1a	PUSH_R	R1	Push R1 to stack
0x1b	POP	R1	Pop 16 bits from stack, store in R1
0x1c	PUSHA	-	Push all general purpose registers to stack
0x1d	POPA	-	Pop all general purpose registers from stack
0x1e	ADD_I	R1, R2, I1	Store R2 + I1 to R1
0x1f	ADD_R	R1, R2, R3	Store R2 + R3 to R1
0x20	SUB_I	R1, R2, I1	Store R2 - I1 to R1
0x21	SUB_R	R1, R2, R3	Store R2 - R3 to R1
0x22	MUL_I	R1, R2, I1	Store R2 * I1 to R1
0x23	MUL_R	R1, R2, R3	Store R2 * R3 to R1
0x24	DIV_I	R1, R2, I1	Store R2 / I1 to R1 and R2 % I1 to AC
0x25	DIV_R	R1, R2, R3	Store R2 / R3 to R1 and R2 % R3 to AC
0x26	AND_I	R1, R2, I1	Store R2 & I1 to R1
0x27	AND_R	R1, R2, R3	Store R2 & R3 to R1
0x28	OR_I	R1, R2, I1	Store R2 | I1 to R1
0x29	OR_R	R1, R2, R3	Store R2 | R3 to R1
0x2a	XOR_I	R1, R2, I1	Store R2 ^ I1 to R1
0x2b	XOR_R	R1, R2, R3	Store R2 ^ R3 to R1
0x2c	NOT	R1, R2	Store ~R2 to R1
0x2d	SHL_I	R1, R2, I1	Store R2 << I1 to R1
0x2e	SHL_R	R1, R2, R3	Store R2 << R3 to R1
0x2f	SHR_I	R1, R2, I1	Store R2 >> I1 to R1
0x30	SHR_R	R1, R2, R3	Store R2 >> R3 to R1
0x31	CMP_I	R1, I1	Set comparison flags
0x32	CMP_R	R1, R2	Set comparison flags
0x33	JMP_I	I1	Set IP to I1
0x34	JMP_R	R1	Set IP to R1
0x35	JEQ_I	I1	Set IP to I1 if equal (Z=1)
0x36	JEQ_R	R1	Set IP to R1 if equal (Z=1)
0x37	JNE_I	I1	Set IP to I1 if not equal (Z=0)
0x38	JNE_R	R1	Set IP to R1 if not equal (Z=0)
0x39	JLT_I	I1	Set IP to I1 if less (C=1)
0x3a	JLT_R	R1	Set IP to R1 if less (C=1)
0x3b	JGT_I	I1	Set IP to I1 if greater (Z=0 and C=0)
0x3c	JGT_R	R1	Set IP to R1 if greater (Z=0 and C=0)
0x3d	JLE_I	I1	Set IP to I1 if less or equal (Z=1 or C=1)
0x3e	JLE_R	R1	Set IP to R1 if less or equal (Z=1 or C=1)
0x3f	JGE_I	I1	Set IP to I1 if greater or equal (C=0)
0x40	JGE_R	R1	Set IP to R1 if greater or equal (C=0)
0x41	CALL_I	I1	Push IP to stack, set IP to I1
0x42	CALL_R	R1	Push IP to stack, set IP to R1
0x43	RET	-	Pop 16 bits from stack, store in IP
0x44	HALT	-	Halt execution
0x45	*PRINT_I	I1	Print value of I1 to stdout
0x46	*PRINT_R	R1	Print value of R1 to stdout

* Might be modified or removed