Reverse Engineer the Spectre GCR?
- Thread starter JustG
- Start date
Maybe you can contact David Small?
He has a website: https://davidsmallstoryteller.wordpress.com/about/
And a not very active Facebook page: https://m.facebook.com/profile.php/?id=748538110&name=xhp_nt__fb__action__open_user
* I’ve got one coming in a week or two to tinker with. Just posted in another thread on here asking if anyone knows about the GCR being able to read Mac formatted SCSI disks. I read somewhere online that it could do this. But I didn’t think the ST HD port was SCSI. Thought it was ACSI only.
He has a website: https://davidsmallstoryteller.wordpress.com/about/
And a not very active Facebook page: https://m.facebook.com/profile.php/?id=748538110&name=xhp_nt__fb__action__open_user
* I’ve got one coming in a week or two to tinker with. Just posted in another thread on here asking if anyone knows about the GCR being able to read Mac formatted SCSI disks. I read somewhere online that it could do this. But I didn’t think the ST HD port was SCSI. Thought it was ACSI only.
AFAIK, yes. I *do* have an original - Adaptec even - card that "translates" ACSI to SCSI. I used it back when my GCR was new along with another card that "translated" SCSI to ST-506!! I ran 2 x 30Mb IBM ST-506 5 1/4" HDDs off the pair - with TOS and Mac partitions connected to my self-upgraded 4Mb 520stfm.
Interesting. So you mean yes ACSI only so No it can’t read Mac SCSI disks out of the box?AFAIK, yes. I *do* have an original - Adaptec even - card that "translates" ACSI to SCSI. I used it back when my GCR was new along with another card that "translated" SCSI to ST-506!! I ran 2 x 30Mb IBM ST-506 5 1/4" HDDs off the pair - with TOS and Mac partitions connected to my self-upgraded 4Mb 520stfm.
Guys, I don't have Spectre GCR schematics or code anymore.
There's a D to A converter that sets a voltage controlled oscillator to determine the frequency the GCR reads Mac floppy data at.
The Mac used 5 different speeds, changing every 16 tracks, so I had to dance with it to change read/write speed..
The PAL decodes Mac GCR to an 8 bit register I'd read/write. GCR uses 6 bits encoded into 8 bits to ensure clock transitions. Then you take 4 bytes of raw data from the GCR hardware, shift and mask, you get out 24 bits total, that produces 3 8 bit bytes. The trick is doing it on the fly, so no interrupts allowed, so you could handle 1:1 interleave, pick up a whole track's sectors one by one.
Believe me, shutting off the keyboard and mouse was a nightmare! You can't just go IPL 7. The keyboard chip keeps sending data, there's some hassle about edge vs. Level triggering, and it hangs. Finally found totally undocumented that you can ask the keyboard to be quiet a bit. Much like X-on, X-off. Then you do the GCR stuff, wake up the keyboard, and procrss all ghe interrupts. I think wild mouse movement during GCR made it still lock up.
The rest of the hardware mapped the two ROMs one at a time into one 64K window of the cartridge, then the other. The upper 64K was control and I/O for the GCR stuff.
I just don't have this stuff anymore. You know how it goes. You move, stuff gets lost. Ive moved several times.
Youre welcome to email me at:
[email protected]
-- Dave Small
There's a D to A converter that sets a voltage controlled oscillator to determine the frequency the GCR reads Mac floppy data at.
The Mac used 5 different speeds, changing every 16 tracks, so I had to dance with it to change read/write speed..
The PAL decodes Mac GCR to an 8 bit register I'd read/write. GCR uses 6 bits encoded into 8 bits to ensure clock transitions. Then you take 4 bytes of raw data from the GCR hardware, shift and mask, you get out 24 bits total, that produces 3 8 bit bytes. The trick is doing it on the fly, so no interrupts allowed, so you could handle 1:1 interleave, pick up a whole track's sectors one by one.
Believe me, shutting off the keyboard and mouse was a nightmare! You can't just go IPL 7. The keyboard chip keeps sending data, there's some hassle about edge vs. Level triggering, and it hangs. Finally found totally undocumented that you can ask the keyboard to be quiet a bit. Much like X-on, X-off. Then you do the GCR stuff, wake up the keyboard, and procrss all ghe interrupts. I think wild mouse movement during GCR made it still lock up.
The rest of the hardware mapped the two ROMs one at a time into one 64K window of the cartridge, then the other. The upper 64K was control and I/O for the GCR stuff.
I just don't have this stuff anymore. You know how it goes. You move, stuff gets lost. Ive moved several times.
Youre welcome to email me at:
[email protected]
-- Dave Small
