Virtual machine

Specially designed virtual machine is useful for testing compiler, operating system and it is also necessary for running applications under operating system which need to be CPU architecture independent and should be either interpreted or compiled to native code.

Objectives

• Support various data width (bit width 8, 16, 32, 64, ...)
• Simple to be implemented
• Effective execution also in interpreting mode
• Mostly register oriented instructions
• Stack support
• Instruction set should be extensible

Features

• Instructions
  • Constant loading
  • I/O ports
  • Stack
  • Subroutines
  • Jumps
  • Arithmetic operations
  • Logic bitwise operations
  • Bit manipulation
  • Shifts
  • Special instructions
• Registers
• Memory addressing
• Flags
• Interrupt system

Instructions

Code	Short name	Full name	Description
0	NOP	No operation
1	CP Op1, Op2	Copy	Copy data from one operand to another
2	CMP Op1, Op2	Compare	Compare two operands
3	INC Op1	Increment	Increment operand by one
4	DEC Op1	Decrement	Decrement operand by one
5	IN Op1, (Op2)	Input	Read data to Op1 from I/O port Op2
6	OUT (Op1), Op2	Output	Write data Op2 to I/O port Op1
7	HALT	Halt	Stops execution of program
8	ADD Op1, Op2	Addition	Add Op2 to Op1
9	SUB Op1, Op2	Subtraction	Subtract Op2 from Op1
10	MUL Op1, Op2	Multiplication	Multiply Op1 by Op2
11	DIV Op1, Op2	Division	Divide Op1 by Op2
12	MOD Op1, Op2	Modulo	Set Op1 to remainder of division of Op1 by Op2
13	AND Op1, Op2	Logical AND	Set Op1 to logical AND of Op1 and Op2
14	OR Op1, Op2	Logical OR	Set Op1 to logical OR of Op1 and Op2
15	XOR Op1, Op2	Exclusive OR	Set Op1 to logical XOR of Op1 and Op2
16	CALL Op1	Call subroutine	Store return address to stack and jump to given address by Op1
17	RET	Return from subroutine	Return to address stored on top of stack
18	SHL Op1	Shift left	Shift all bits in Op1 to the left
19	SHR Op1	Shift right	Shift all bits in Op1 to the right
20	JP Op1	Jump to absolute address	Set program counter to new absolute address
21	JR Op1	Jump to relative address	Set program counter to new address relative from current
22	PUSH Op1	Push to stack	Put Op1 to the top of stack
23	POP Op1	Pop from stack	Pop Op1 from the top of stack
24	BIT Op1, Op2	Test bit	Test if bit at position Op2 in Op1 is set
25	SET Op1, Op2	Set bit	Set bit at position Op2 in Op1 to 1
26	RES Op1, Op2	Reset bit	Set bit at position Op2 in Op1 to 0
27	MR Op1, [Op2]	Memory read	Read data Op1 from memory address Op1
28	MW [Op1], Op2	Memory write	Write data Op2 to memory address Op1
29	SKIP Op1	Skip next instruction	Skip next instruction if Op1 is non zero
30	SR Op1, {Op2}	Special register read	Read data Op1 from special register Op1
31	SW {Op1}, Op2	Special register write	Write data Op2 to special register Op1

Operands

	Bit width
Register	Native	8-bit	16-bit	32-bit	64-bit	128-bit
Constant	0	16	32	48	64	80
R1	1	17	33	49	65	81
R2	2	18	34	50	66	82
R3	3	19	35	51	67	83
R4	4	20	36	52	68	84
R5	5	21	37	53	69	85
...
R14	14	30	46	62	78	94
R15	15	31	47	63	79	95

Special registers

Code	Short name	Full name	Description
0	PC	Program Counter	Holds pointer to current program execution point
1	SP	Stack Pointer	Memory address to top of the stack
2	DW	Data width (read only)	Native data width (0 - dynamic, 1 - 8-bit, 2 - 16-bit, 3 - 32-bit, 4 - 64-bit, 5 - 128-bit)