Thread
design ideas for a SD-card floppy emulator
Thanks, 6.2.2 does seem to work much more reliably on the Mac Plus. It's still crazy slow when debugging ROM code, but I was able to hit some ROM floppy driver breakpoints. I'm having a hell of a time making any sense of it-- it seems like maybe the super-slow execution in the debugger is throwing all the time-sensitive floppy routines out of whack, or maybe the system patches over some of the ROM routines so they're never actually called. It's definitely better than nothing though!
YAHOOOO!!!!! I was literally jumping up and down and shouting a minute ago, because I got something working!!!!
When the Mac Plus is waiting for a boot disk, I can now push a button to insert the virtual floppy disk image, and produce a Happy Mac on the screen! Because only the first two sectors of the floppy image are loaded, it can't actually boot, but it proves that the right data is traveling from my Rube Goldberg CPLD+MCU setup to the Mac, and the Mac likes it. YES!!!
Luckily my first attempt wasn't far off, because this thing is near impossible to debug. The first problem I found was that the disk RPM speed feedback I thought was working correctly actually wasn't. I was able to use MacsBug to see that the floppy driver was returning error -79 "can't correctly adjust disk speed", but I had to blindly experiment with different speed values until I hit on one that worked. Then the floppy driver was returning error -67 "can't find an address mark", which basically means it can't make any sense of the data to determine where a sector begins. With zero other info to help troubleshoot that, I methodically went through all my design assumptions one-by-one again looking for mistakes, and found a place in the IWM specification where I might have misinterpreted what Woz meant by a transition on the read sense line. I changed it so that a logical 1 produces a falling transition, instead of just any transition, and holy #$%*& it worked.
There's still a bunch more work to do with getting an entire disk image off an SD card, and reading data a track at a time, and disk side 0/1 stuff, but I'm optimistic about those pieces now that the initial task of getting bytes into the Mac is working.
Time for a beer.
When the Mac Plus is waiting for a boot disk, I can now push a button to insert the virtual floppy disk image, and produce a Happy Mac on the screen! Because only the first two sectors of the floppy image are loaded, it can't actually boot, but it proves that the right data is traveling from my Rube Goldberg CPLD+MCU setup to the Mac, and the Mac likes it. YES!!!
Luckily my first attempt wasn't far off, because this thing is near impossible to debug. The first problem I found was that the disk RPM speed feedback I thought was working correctly actually wasn't. I was able to use MacsBug to see that the floppy driver was returning error -79 "can't correctly adjust disk speed", but I had to blindly experiment with different speed values until I hit on one that worked. Then the floppy driver was returning error -67 "can't find an address mark", which basically means it can't make any sense of the data to determine where a sector begins. With zero other info to help troubleshoot that, I methodically went through all my design assumptions one-by-one again looking for mistakes, and found a place in the IWM specification where I might have misinterpreted what Woz meant by a transition on the read sense line. I changed it so that a logical 1 produces a falling transition, instead of just any transition, and holy #$%*& it worked.
There's still a bunch more work to do with getting an entire disk image off an SD card, and reading data a track at a time, and disk side 0/1 stuff, but I'm optimistic about those pieces now that the initial task of getting bytes into the Mac is working.
Time for a beer.
A very hastily-produced video of the floppy emulator in action:
:approve:
Awesome!!!!!!!
Yay, "Lonely" is now a Hardware-Debugging-Happy-Mac. 
Amazing, Bigmessowires, Amazing!!!
Just a thought....has anyone thought about emailing Tim Cook and see if Apple would be interested in turning over some of the early Mac hardware schematics to the hobbyist community? One thing that made Steve Jobs great was his relentless pursuit of the next best thing, but that came with a price of not being nostalgic about his older creations. Perhaps Tm would find our kind of interest amusing, and having no business or financial reason to hang onto these ROMS and schematics and such, make them freeware.
Just a thought....has anyone thought about emailing Tim Cook and see if Apple would be interested in turning over some of the early Mac hardware schematics to the hobbyist community? One thing that made Steve Jobs great was his relentless pursuit of the next best thing, but that came with a price of not being nostalgic about his older creations. Perhaps Tm would find our kind of interest amusing, and having no business or financial reason to hang onto these ROMS and schematics and such, make them freeware.
That is incredible :O
re: emailing Tim Cook...somehow I don't like your chances, but it certainly is a good idea...don't ask don't get.
re: emailing Tim Cook...somehow I don't like your chances, but it certainly is a good idea...don't ask don't get.
It seems you have it working now, but would Macsbug 5.4 be helpful?
I was thinking more along the lines of contacting the woz to see if he could convince the board to release the entire remaining documentation on the Mac from the 128k up through the early PCI/603e architecture as a memorial to the Mac of old, to Steve Jobs and the rest of the Mac's developers. Retro computing is a great way to learn the basics of computing in general, which dovetails nicely with his devotion to educating young minds.re: emailing Tim Cook...somehow I don't like your chances, but it certainly is a good idea...don't ask don't get.
The shine is certainly absent from what were once referred to as the "Crown Jewels" of Apple. :b&w:
I was thinking a similar timeframe. Perhaps, from a hardware level, everything pre-New World ROM. Apple also has system 6 and 7.5 available for free on their site still. Would like to see System 7.x as well as 7.6, 8.0, 8.5, and 9.0.
I think that would be really cool if they did that, but I wouldn't hold my breath. Who knows though...it's software rather than hardware, but they did release the source code (for non-commercial use) to MacPaint and QuickDraw:
http://www.computerhistory.org/highlights/macpaint/
http://www.computerhistory.org/highlights/macpaint/
:O
We're not worthy! We're not worthy!
Astounding!
A possible approach might be - "as much as possible, please sirs, starting with the oldest." Contacting Woz is probably not a bad idea - at the very least, he might be tickled to see someone in 2011 interrogating the old Integrated Woz Machines
My understanding from previous discussions along these lines is that these versions integrate too much proprietary third party (ie, non-Apple) code, making chasing down all the licences a nightmare. Half of those indie developers would be out of business.
I'm this close to having a read-only floppy emulator fully working now with my Mac Plus, but there's some stepping bug or glitch somewhere that's eluding me. It actually works about 95% of the time you read a sector, but then eventually a read will fail with some kind of synchronization error. I think the Mac believes it's on a different disk track than the emulator does. The Mac will start to boot from the virtual floppy disk, then give up and eject it. If I boot from a hard disk, and then insert the virtual floppy, usually I can get it to mount in the Finder and see all the file icons, but if I try to open any of the files I get an I/O error.
It must be a silly bug somewhere, but after hours of searching for the cause I still can't find it. Maybe it will make more sense tomorrow...
It must be a silly bug somewhere, but after hours of searching for the cause I still can't find it. Maybe it will make more sense tomorrow...
Keep up the good work! :beige:
This is a very exciting project that I'm sure is being closely watched by a lot of hobbyists that lurk here on this forum.
I really want to build one of these sometime in the near future!
This is a very exciting project that I'm sure is being closely watched by a lot of hobbyists that lurk here on this forum.
I really want to build one of these sometime in the near future!
I'm lurking...good work!! :
Hey johnathan, that's an interesting concept for your avatar you have there, do you have a higher res. available to check out?
Hey johnathan, that's an interesting concept for your avatar you have there, do you have a higher res. available to check out?
I've got it pretty much working now. Will tidy it up a little and start a new thread in the Hacks forum, since this isn't really "design ideas" anymore!