Simple Fantasy CPU VM

Compile with make

Assemble a program with -a file.asm -o output.rom to assemble a binary rom that targets the VM.

Run the program rom with -r output.rom

Instruction set

,----------------------------------------------.
| NOP |             |           |              |
|-----+-------------+-----------+--------------|
| LDW | 00  dst src | 00000 ofs |              |
|     | 01  dst src | 2 byte ofs literal       |
|     | 10  dst     | 2 byte src address       |
|     | 11  dst     | 2 byte src literal       |
| LDB | 00  dst src | 00000 ofs |              |
|     | 01  dst src | 2 byte ofs literal       |
|     | 10  dst     | 2 byte src address       |
| STR | 00  src dst | 00000 ofs |              |
|     | 01  src dst | 2 byte ofs literal       |
|     | 10  src     | 2 byte dst address       |
| STB | 00  src dst | 00000 ofs |              |
|     | 01  src dst | 2 byte ofs literal       |
|     | 10  src     | 2 byte dst address       |
|-----+-------------+-----------+--------------|
| LAR | 00000   dst | 4 bit src |              |
|-----+-------------+-----------+--------------|
| ADD | 0 m dst op1 | 2 byte int or reg op2    |
| SUB | ...         | ...                      |
| MUL | ...         | ...                      |
| DIV | ...         | ...                      |
| MOD | ...         | ...                      |
| LSL | ...         | ...                      |
| LSR | ...         | ...                      |
| AND | ...         | ...                      |
| ORR | ...         | ...                      |
| XOR | ...         | ...                      |
|-----+-------------+--------------------------|
| COM | 0000 m reg  | 2 byte literal or reg    |
|-----+-------------+--------------------------|
| PSH | 0000 m reg  | 2 byte literal           |
| POP | 00000 reg   |           |              |
| CMP | 00000 op1   | 00000 op2 |              |
| JMP | metric byte | 2 byte label address     |
| JSR | metric byte | 2 byte label address     |
| RET |             |           |              |
| INT | interrupt   |           |              |
`----------------------------------------------'

Comparison metrics

.--------------------.
| NC | No condition  |
| EQ | Equal         |
| NE | Not Equal     |
| LT | Less thanion  |
| GT | Greater than  |
| LE | Less Equal    |
| GE | Greater Equal |
`--------------------'

Calling convention

All the responsibility of cleanup lies within the called procedure.

	LDW R0 #5
	LDW R1 #6
	PSH R0        ; push arg 1
	PSH R1        ; push arg 2
	JSR NC add    ; jump to subroutine
	POP R0        ; retrieve return value
	INT END

add:
	LAR R1 FP     ; load auxiliary register (frame pointer)
	ADD R1 R1 #x1 ; add 1 to get previous element in stack
	LDW R3 R1 #x8 ; load stack address offset 8 bytes from the frame pointer (arg 2)
	LDW R2 R1 #xc ; load stack address offset 12 bytes from the frame pointer (arg 1)
	ADD R2 R3 R2  ; function body
	PSH R2        ; push return value
	RET           ; return to previous stack frame

Inclusion

At the top of your assembled file, you can include other files to paste in to be assembled in that order.

+examples/heap

Interrupts

.-------------------------------------------------------------------,
| OUT | Print ascii string to stdout | R0 <- address, R1 <- length  |
| KBD | Get keyboard key status      | (unimplemented)              |
| END | End the program and return   | R0 <- process return code    |
`-------------------------------------------------------------------'

Invoking interrupts requires loading arguments into registers.

	LDW R0 #0       ; load program rom return code
	INT END         ; call interrupt to end program