Warning
Consider this to be in alpha stage. Currently supports all 68k instructions that are validated with about 22,000 tests but the code might still contain bugs. If you find bugs then don't hesitate reporting them, since the hardest part is to find the bugs while it might be way easier to fix them.
The fasm68k instruction set adds support to assemble assembly code for the Motorola 68000 cpu with Tomasz Grysztar's fasmg.
Here you can see what was needed to adapt BigEvilCorporation's megadrive_samples for fasm68k.
Linux
Get fasm68k and it's dependences (i.e. fasmg and examples) by running:
git clone --recurse-submodules [email protected]:fredrik-hjarner/fasm68k.gitStep into the repository directory:
cd fasm68kScript must be executable:
chmod +x fasm68kTo assemble the examples run these commands and binary files should be created which you can run in a Mega Drive/Genesis emulator:
./fasm68k examples/megadrive_simple_demo/main.asm ./fasm68k examples/megadrive_samples_fasm68k/1_hello_world/hello.asm ./fasm68k examples/megadrive_samples_fasm68k/2_scroll_planes/scroll.asm ./fasm68k examples/megadrive_samples_fasm68k/3_sprites/sprites.asm ./fasm68k examples/megadrive_samples_fasm68k/4_gamepad/gamepad.asm ./fasm68k examples/megadrive_samples_fasm68k/6_psg_tone/psg_tone.asm ./fasm68k examples/RetailClerk89_fasm68k/src/RetailClerk89.X68 ./fasm68k examples/speedrun-tower_fasm68k/src/SpeedrunTower.X68Add a new line at the bottom of your .bashrc file adding the fasm68k directory to the PATH so you can run fasm68k from anywhere and not only from the specific folder you cloned it into:
export PATH=$HOME/code/fasm68k:$PATH
Windows
TODO
Mac
Unfortunately you're out of luck. fasmg only runs on x86 processors (since it is written in assembly), so you would need to run a virtual machine with either Windows or Linux then follow the Linux or Windows inbstructions.
Beyond the standard fasmg directives and keywords, fasm68k adds the following ones:
| Directive/ keyword |
Description | Also present in these assemblers |
|---|---|---|
__rs |
Current value of RS counter | asm68k |
rsset |
Set __rs address. |
asm68k |
even |
Word-align the current address. | asm68k, vasm |
rseven |
Word-align the __rs address. |
|
rs.b |
Reserve a byte of space. | asm68k |
rs.w |
Reserve a word of space. | asm68k |
rs.l |
Reserve a longword of space. | asm68k |
dc.b |
Define a byte. | asm68k, vasm |
dc.w |
Define a word. | asm68k, vasm |
dc.l |
Define a longword. | asm68k, vasm |
incbin |
Include a binary file. | asm68k, vasm |
- Macros are completely different and it's the main reason for this project to exist. fasmg's macro langauge is more powerful than the macro languages of other assemblers. Check out fasmg's manual for more information.
- fasm68k is less pedantic when it comes to the use of whitespace. You may place an instruction in the "first column" (without any leading whitespace) for example.
- fasm68k does not support
*to get the current address. Either use@or$instead. - Some operators are different. While I have added support for
<<and>>for bit shifting, the preferred way is to useshlandshr. Likewise try to useorinstead of|andandinstead of&. - Binary numbers are written as
01010101b(instead of%01010101). - You prefix labels with dot
.label1to make them local (instead of prefixing with @@label1). - Currently no optimizations and might be missing some aliases for some instructions.
In comparison to vasm (vasmm68k_mot)
### ORG
ORGworks very differently in vasm and fasmg. In fasmg the addresses in afterORGare based on the value specified in the argument. In vasm theORGcommand actually adds empty bytes up to the specified address.
- I will add a compatibility setting to support the vasm behaviour. It is recommended to have that setting disabled unless you need it.
- 2025-03-28:
- Humble beginnings: Initial implementation of
nop,rteandrts.
- Humble beginnings: Initial implementation of
- 2025-05-05:
- Alpha "release".
- Rudimentary implementation of all 680000 instructions and all addressing modes.
- First commit to the
fasm68krepository.
- 2025-05-06:
- fasm68k can correctly assemble all BigEvilCorporation's
megadrive_samples.
- fasm68k can correctly assemble all BigEvilCorporation's
- 2025-05-12:
- fasm68k can correctly assemble Hugues Johnson's RetailClerk89. It took about 30-40 hours to get it to produce identical binary.
- 2025-05-13:
- fasm68k can correctly assemble Hugues Johnson's Speedrun Tower. It took 45 minutes to get it to run in an emulator and about 1 hour to produce identical binary.
- Tomasz Grysztar for fasmg.
- BigEvilCorporation for the megadrive_samples which I simply adapted for fasm68k.
- The vasm and clownassembler assemblers were very helpful for determining correct behaviour of the encoding of the instructions.
- Hugues Johnson's RetailClerk89 and Speedrun Tower were great games to test fasm68k with.
- Exodus and Kega Fusion emulators were used to test the output of fasm68k.
- This m68k encoding pdf by GoldenCrystal was extremely helpful.