Now that the machine has been running on a (very slightly modified) version of 1.5, I figured it would be a good time to start thinking about fixing some small bugs or other annoyances and maybe add some features. In order to do so, I need an easy way to upload a new version to the system.
While the original Melcard stuff has been basically reverse engineered and ready to go, I can read these cards on the system, but not yet write to one from my computer.
To originally get the OS loaded, I used an EPROM with a small adapter board that basically mimicked a Melcard.
If I can hook up that thing, but with an EPROM Emulator I can connect to USB, I would be set.
A few caveats came into play.
The original code did a dual check to see if a card presented indeed contained a valid OS.
it looked for an OS string and calculated a checksum. After some poking around and creating a modified bootloader rom, I discovered that the OS label was valid, but it always failed on the checksum part.
I now worked out how that worked and how I can create a full OS EPROM that validates both checks, but it took a lot of back and forth between adjusting the bootloader code, burning EPROMS and re-check. For now I’ve opted to completely hack out the checksum code – I’ll add it back in later as for now I want to focus on a good quick OS improvement workflow.
A few things on my todolist:
Right now I’m relying on my very old XP pc to run the build, as the compiler is DOS based.
I want to see if I can get that to work on an XP emulation on my mac. XP is already running, but getting a shared folder seems to be more involved than expected. Dosbox-X may be an alternative.
