m68kemu

A very minimalistic Motorola 68000 user-mode emulation written in Kotlin, with the actual cpu core emulation being less than 750 lines of code.

It can be used to emulate short pieces of 68000 binary code.

I used it for validation of the Raspberry Casket Pretracker replayer.

I had it lying around for so many years, I thought I could just publish it and maybe someone finds it useful.

Features

Memory access abstraction
User-mode only (no exceptions, interrupts, supervisor-instructions etc.)
Instructions not implemented (might not be decoded correctly!):
- abcd, sbcd, nbcd
- movep, cmpm, addx/subx/tas on memory
- ori/andi/eori to CCR/SR, move from SR, move to CCR/SR, move USP
- illegal, trap, trapv, chk, stop, reset, rte, rtr

Note: Illegal (unavailable) addressing modes may not be detected as such. No 68020+ instructions or addressing modes are supported.

Usage

Create an instance of M68kCpu():

val cpu = M68kCpu()

Create some memory, custom chips, etc:

val ram = Ram(0x0, 0x10000)
val rom = Rom(0xfc0000, kickromimage)
val customChips = CustomChips()

ram.writeWord(0x100, 0x4e75) // just an rts

Configure your system, registers, program counter and run decode() for every instruction as long as you like:

with(cpu) {
    memRegions.add(ram)
    memRegions.add(rom)
    memRegions.add(customChips)

    a[7] = ram.start + ram.size // setup stack register
    pushStack(OpSize.OS_LONG, 0) // write 0 return address
    pc = 0x100 // start of program

    while (pc != 0) {
        decode()
    }
}

The CustomChip classes are minimal stubs. There's also some Paula-Recorder class you might find useful.

1.7 KiB Raw Permalink Blame History

m68kemu

Features

Usage

1.7 KiB

Raw Permalink Blame History