Trying to emulate an Ohio Scientific C1P-MF in Java

[retrohimpi]

I'm trying to write my own Java emulation of a dual floppy Ohio Scientific Challenger 1P and I've been blogging here about my problems with getting it to boot from a disk image. I'm not sure how to link to my blog posts, but you can access them via my profile page.

If anyone has a real C1P and can enlighten me about what happens when it boots from a floppy disk, I'd be most grateful. Although I started out with a C1P in 1979, I couldn't afford a disk drive at the time so I'm not familiar with how it behaved.

 

[tezza]

Good luck. I don't have a floppy for my C1P so I can't help unfortunatey.

There are a few Challenger 1P emulators out there. One way forward might be to get hold of the authors. They will probably have the information you are seeking.

Tez

 

[retrohimpi]

Good luck. I don't have a floppy for my C1P so I can't help unfortunatey.

Shame, I didn't see any mention of floppy drives in your webpages, but thought you might have added one later. It's pretty limiting to have only tape for I/O. Thanks anyway, though.

There are a few Challenger 1P emulators out there. One way forward might be to get hold of the authors. They will probably have the information you are seeking.

Thanks, I'll certainly try this as a last resort, but it feels a bit like cheating to me. All I need is a little assistance with distinguishing between bugs in my drive emulation, possible errors in the disk image and lingering bugs in my 6502 CPU emulation. I was able to work through all the problems I encountered with the original cassette-based emulator because I could still remember how the original hardware behaved, but I couldn't afford to add a disk drive at the time (they were about 3-4 times the cost of the single-board itself) and so I'm not sure what's normal and what's of my own making and it's very frustrating to have no screen output of any kind to hint at what's going wrong or where.

The nearby Centre for Computing History at Haverhill has a disk-based Challenger in its collection, which I'm hoping to see when I get around to arranging a visit and, if I'm still stuck, I might even consider hiring it for a day to familiarise myself with its user interface. Hopefully, dogged persistence and some luck will get me past my current problem (as it did when I was trying to debug my Challenger keyboard matrix). However, the recent spell of fine weather has left me short of time to sit over a hot computer so it may be a few days before I get back to debugging my emulator.

 

[retrohimpi]

Hooray! I've just been able to get it to boot by changing the I/O distributor bytes on the boot disk so that it writes to its screen and doesn't execute the BEXEC* program on the disk. See my latest blog entry for the details and another screenshot.

 

[tezza]

Hooray! I've just been able to get it to boot by changing the I/O distributor bytes on the boot disk so that it writes to its screen and doesn't execute the BEXEC* program on the disk. See my latest blog entry for the details and another screenshot.

Sounds like you're getting there.

Yes, no disk drives on my CP1. Disk drives on a CP1 were an expensive optional extra. As it's really just a collectable model for show, I'll stick with the cassette interface. If it was a later model that was usually sold with drives, I would indeed be looking for them.

Tez