VIRTUAL16

16-bit virtual microprocessor implemented in MOS6502 assembly, inspired by Steve Wozniak's SWEET16. It's under 1k and ROM friendly.
If you want to assemble src/VIRTUAL16.asm file you can use naken_asm or another 6502 assembler.
For assembling your own VIRTUAL16 code go to here, scroll to end of page and write your program there. Make sure you selected "Comma-seperated Hex" option (it's default). Press assemble and place bytes to your 6502 program. Don't forget to prepend 'DB' each line.

Example

Example 6502 assembly file:

.6502
;If you're not placed VIRTUAL16 to your ROM/RAM/EEPROM before uncomment include line.
;Default location of VIRTUAL16 is 0x0400. If you want to change edit VIRTUAL16.asm file
;.include "src/VIRTUAL16.asm"

;If you're placed VIRTUAL16 to your ROM/RAM/EEPROM before, uncomment equ line
;.EQU VIRTUAL16 0x0400 	;Replace if VIRTUAL16 placed different location
.ORG 0x0200				;Replace if you want to place your program different location

MAIN:
    JSR VIRTUAL16
;VIRTUAL16 Instructions
    DB 0x70, 0x00, 0x00, 0x10, 0x00, 0xa0, 0xfc, 0x00
;VIRTUAL16 Instructions
    BRK

Using VIRTUAL16 instructions as 6502 subroutine

You can use VIRTUAL16 instructions as native subroutines. Because of fetch and decode stages eliminated, execution speed is much faster than VIRTUAL16 mode. All instructions process 16-bit data. Here is the list of instructions

ADD16: ZP,y = ZP,x + ZP,y
ADC16: ZP,y = ZP,x + ZP,y + Carry
SUB16: ZP,y = ZP,x - ZP,y
SBC16: ZP,y = ZP,x - ZP,y - !Carry
INC16: ZP,x = ZP,x + Acc
DEC16, ZP,x = ZP,x - Acc
SWAP16: ZP,y = ZP,x / ZP,x = ZP,y
SWAP16: ZP,x[0:7] = ZP,x[8:15] / ZP,x[8:15] = ZP,x[0:7]
UMUL16: 0x18:0x19:0x1A:0x1B = ZP,x * ZP,y (unsigned)
SMUL16: 0x18:0x19:0x1A:0x1B = ZP,x * ZP,y (signed)
AND16: ZP,y = ZP,x & ZP,y
OR16: ZP,y = ZP,x | ZP,y
XOR16: ZP,y = ZP,x ^ ZP,y
ASL16: ZP,x = ZP,x << y (ZP,x[0] = 0)
LSL16: Same as INSASL
ASR16: ZP,x = ZP,x >> y (ZP,x[15] = 0)
LSR16: ZP,x = ZP,x >> y (ZP,x[14] = ZP,x[15])
RLC16: ZP,x = ZP,x << y (ZP,x[0] = Carry)
RRC16: ZP,x = ZP,x >> y (ZP,x[15] = Carry)

To make include (.inc) file assemble VIRTUAL16 using tools\compile.sh script and run makeinclude.py (python3).

Documents

Please check docs folder for more information

TODO

More documentation
Write tests

Known bugs

Nothing yet

Warning

This software is still in beta stage. Even ISA is not finalized. Use at your own risk

Thanks

Thanks to mikeakohn for naken_asm project
Thanks to hlorenzi for customasm project
Thanks to 6502 community