How to: upgrade a 520/540 to a 550c ROM

[frontein1]

You beat me to it I was just typing this. I bet the driver number for the ROMDISK is likely causing this. The number I chose is right in the middle of a bunch of other resident drivers. So next patch we will want to find a better driver number.

As for the ROMDISK itself, looks like it is there just not opened. Give this a try. When the console comes up, type in ROMDISK. Then check Tattletech again to see the status. Hopefully this mounts the ROM disk in the Finder. If not try Rob Brown's dumpdrives. You can enter the drive number in there and post a disk event as well.

 

[croissantking]

After typing ROMDISK and pressing enter, I see the following flash up for a split second, then I crash with an illegal instruction.

 

[frontein1]

OK, I must have something terribly wrong in that driver. I'll port this over to like a Quadra so I can do some on the fly troubleshooting. More to come!

 

[croissantking]

I wonder what desktop ROM the 500 series is most closely related to. It’s 2MB, so would that be the AV Quadras?

 

[frontein1]

I wonder what desktop ROM the 500 series is most closely related to. It’s 2MB, so would that be the AV Quadras?

Yes I was wondering this too. Can we boot a Quadra with the 550c ROM, essentially how 'universal' is that ROM? Q605 or Q840av might be good candidates to try. I'll give this a whirl.

 

[frontein1]

Can we boot a Quadra with the 550c ROM, essentially how 'universal' is that ROM?

Well test failed. At least, cannot boot a Q605 using either the 540c or 550c ROM. Might have to wait until this weekend, but I will give it a try on my Q840av as well.

In the meantime, I did confirm that the v0.90 driver works OK on my Q605, but only on the disk without the embedded SCSI driver. So with that said we can give it another go, with these changes:

• Use a different ID so we don't conflict with the existing ROM and System drivers for the 550c. Maybe slot 60 refNum -61, I think that might be safe based on your earlier screenshot. I pulled up the Apple Developer notes and that is in the unreserved range too.
• Use a 2MB disk without the embedded SCSI driver.

Of course I have the easy job of putting the ROM file together. Your job @croissantking of desoldering, programming and resoldering is more labor intensive.

Is there an emulator that can take handle a 2MB or even a 4MB ROM file?

 

[frontein1]

OK and I have a confession to make @croissantking I read your other post about the ROM base being 4000 0000 in the 550c. And when I first put the custom ROM together, I incorrectly assumed that the ROM base was the same as the earlier Quadra models (4080 0000). So assuredly this was also part of the reason the driver was failing on the 550c (and why it was working on the Q605).

Which was really dumb of me, because I knew that the ROM disk started at 4020 0000. So why I thought that the ROM started at 4080 0000 is beyond me!

So with that said, here are the accumulated changes we can consider for the next test.

• Use a different ID so we don't conflict with the existing ROM and System drivers for the 550c. Maybe slot 60 refNum -61, I think that might be safe based on your earlier screenshot. I pulled up the Apple Developer notes and that is in the unreserved range too.
• Use a 2MB disk without the embedded SCSI driver.
• Change ALL absolute addresses from 408 to 400 in the driver.