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| Author | PCI-PCI Bridge cards no longer a bridge too far for Gazelle! (Read 20855 times) | ||||||||||||||||||||||||||||||
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Tech_and_Music
8 MB  Posts: 10 Tech&Music 
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on: December 24, 2022, 22:30
Some good news for the owners of PowerMac/Performa 5500 and 6500, or even the infamous Twentieth Anniversary Macintosh! A long standing bug in OpenFirmware, that prevented cards utilizing PCI-PCI bridge chips, has finally been fixed! PCI-PCI bridge chips are used on cards that are effectively multiple PCI cards in a long trenchcoat, running a PCI bus on the other end towards the various chips. Sonnet made the Trio card, combining ATA, FireWire and USB, but various others, including no-name cards combining SiI3112 SATA, FireWire and USB, also exist. The SATA cards have been particularly interesting, as with a ROM swap, they can run the SeriTek firmware that allows SATA disks to work in Classic Mac OS, masquerading as a SCSI bus to the OS. However, in the 6500, 5500, and TAM, all using the Gazelle board, these PCI-PCI bridge cards did not work. For some reason, OpenFirmware would see the PCI-PCI bridge chip, but would not enumerate the devices beyond the bridge. The 6400/5400 Alchemy board did not have these problems, nor did any other Macs. Sonnet had a solution for their card, by writing a NVRAMRC script that manually laid out the devices for OpenFirmware, so the Mac could detect and interface with the devices on the card. However, this was device specific, and rather treating the symptom than the problem. Later revision Sonnet cards didn't work with the patch, despite being the same product, because they used different revisions of the bridge and controller chips. Over on 68kMLA, I pitched the idea back in 2021 to the forums to see if the patch could be modified for the use with the SATA/FW/USB card, after swapping such a card for a Radeon card with Knezzen, as his 5500 couldn't use the card. User Cheesestraws put in a valiant effort, and did get it mostly working. However, after dosdude1 made a video on the same type of card two weeks ago, interest in the thread quickly grew, leading OpenFirmware wizard joevt to enter the thread and tackle the problem. In the following post, he managed to find and eliminate the problem entirely. (modern browser needed) It appears that the ATi fCode in the Gazelle ROM is bugged, leading to OF no longer being able to enumerate beyond the bridge chip after it had been initialized. The fix in the proposed NVRAMRC script is a simple but effective solution (though complicated to understand for us mere mortals!): Get to the ATi fCode last, after the devices beyond the bridge are already properly enumerated. This fixes the problem itself, and allows any PCI-PCI bridge based card with compatible devices on it to work with these Macs. And that's great news, as these Macs either have two, or even just a lone PCI slot. While these cards have gotten hard to come by, it is nice that these machines now have the ability to utilize them. And a quarter-century old bug has been eliminated. Somewhere, the poor Sonnet engie who painstakingly wrote the original NVRAMRC script screamed in agony, and has no idea why 
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Last Edit: December 25, 2022, 16:05 by Bolkonskij
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Bolkonskij
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Administrator 1024 MB  Posts: 2023
Reply #1 on: December 25, 2022, 16:09
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Great to have you here again, Tech & Music! Drop by more often, especially with such good news for owners of 5500 & 6500s. It's amazing what level of talented and dedicated people our community has! (Sitenote: I edited a link in your post and added an info that a modern browser is needed to view it... me and others are usually on System 7 when here :-) )
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Knezzen
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Administrator 512 MB Posts: 608 Village idiot
Reply #2 on: December 26, 2022, 13:27
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Wonderful news and great detective work!
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cballero
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1024 MB Posts: 1176 System 7, today and forever
Reply #3 on: December 26, 2022, 15:38
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Wow, that's a real cool fix, Tech and Music!! This is a great example of the kind of community knowledge and involvement where interest sparks skilled programmers to tinker on some neat software that give retro Macs the next generation of hacks, tools, games and productivity software!  I wish some of our Mac sites would have forum polls to see what peeps would love to see worked on and someday built.. wait, does S7T have this capability? 
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Bolkonskij
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Administrator 1024 MB Posts: 2023
Reply #4 on: December 27, 2022, 18:59
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Not as a poll, but why not post an open thread "what updates / fixes stuff do you wish for in 2023 and beyond?". Or whatever. Go ahead 
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cballero
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1024 MB Posts: 1176 System 7, today and forever
Reply #5 on: December 28, 2022, 04:14
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Right! Wait, I don't know of any thing to fix, aside from the little list of programming wishes we made with BBG over at the MG, which he worked on and got two of the them just about finished.. until his iMac G3 crashed and blew all of his programming efforts away, so know those two programs will remain wish-list items (at least for now) 
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Bolkonskij
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Administrator 1024 MB Posts: 2023
Reply #6 on: December 29, 2022, 06:41
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You never know you wanted something until it pops up I've been thinking for eons with Knezzen about setting up some kind of developer resource, possibly even with bounty projects. But given I just launched another project, it might be wiser to leave that to others :-)
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Neal_SE30
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256 MB Posts: 401 System 7 Newcomer!
Reply #7 on: December 29, 2022, 22:20
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Sounds good, yes setup a resource area for all these ideas
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