Introducing ZuluSCSI Blaster - now with More Cowbell!

[David Cook]

the fallback modes are a bit more fiddly than the "classic" equivalents.

Very interesting. Given the faster-clocked CPU, the non-DMA mode must really stink.

architectural limitation on either the software or hardware side that made implementing the DMA untenable.

Apple patched it out in the leaked source. Not sure if it was ever renabled.

; <57> 04-22-90 csd
; commented out the installation of SCSI DMA so we stop trashing
; hard disks on the IIfx.

movea.l SCSIGlobals,a1 ; point to SCSI Manager globals
move.l #250*10000,G_Reserved1(a1) ; set up 250ms byte-to-byte timeout
leaROM ROMFastWriteOSS,a0
; move.l a0,jvVFWO(a1) ; use DMA code for SCSIWBlind
leaROM ROMFastReadOSS,a0
; move.l a0,jvVFRO(a1) ; use DMA code for SCSIRBlind

 

[Arbee]

I've been told the issue was that they couldn't get DMA to play nice with System 7 virtual memory. So if VM was on you'd get random trashing of disks and memory. That isn't *that* hard of a problem, and they obviously did work it out later for the PowerMacs.

Incidentally, 04-22-90 is almost a month after the IIfx shipped. So presumably the machines initially shipped with an enabler that allowed DMA to work and they very quickly got complaints. Would be interesting to dig up that enabler, but I have very little hope of it happening.

ETA: DMA was never enabled for the IIfx in Mac OS. All the way out to 7.6.1, the end of the line for 68030, it uses the PIO fallback.

 

[David Cook]

So presumably the machines initially shipped with an enabler that allowed DMA to work and they very quickly got complaints.

I am considering hacking that code back in to see what happens.

 

[David Cook]

Back on the topic of this thread. I encountered something a little weird.

On a completely recapped IIsi, with the Blaster attached externally and an internal Quantum ProDrive, the SCSI doesn't work. The ProDrive won't even spin up.

* If you plug a power cord into the Blaster, then everything works fine.
* If you use the ZuluSCSI v1.1 (no power cord) instead of the Blaster, then everything also works fine.
* If you remove the ProDrive, the Blaster works fine without the power cord.

So, maybe a difference in inrush current or power requirements? Maybe I'm just pushing the power limit on the IIsi? Not a big deal. Just worth noting.

 

[zigzagjoe]

Back on the topic of this thread. I encountered something a little weird.

On a completely recapped IIsi, with the Blaster attached externally and an internal Quantum ProDrive, the SCSI doesn't work. The ProDrive won't even spin up.

* If you plug a power cord into the Blaster, then everything works fine.
* If you use the ZuluSCSI v1.1 (no power cord) instead of the Blaster, then everything also works fine.
* If you remove the ProDrive, the Blaster works fine without the power cord.

So, maybe a difference in inrush current or power requirements? Maybe I'm just pushing the power limit on the IIsi? Not a big deal. Just worth noting.

AFAIK the IIsi lacks internal termination power entirely - I'm kind of curious how the other zuluscsi board is working at all unless it's managing to backfeed enough power from the logic board's termination or something equally odd.

It should have external termination power AFAIK so your primary case there ought to work though. Might be worth probing the internal power rail of the zuluscsi in both positions to see what you find.

 

[David Cook]

AFAIK the IIsi lacks internal termination power entirely - I'm kind of curious how the other zuluscsi board is working at all unless it's managing to backfeed enough power from the logic board's termination or something equally odd.

It should have external termination power AFAIK so your primary case there ought to work though. Might be worth probing the internal power rail of the zuluscsi in both positions to see what you find.

Both the ZuluSCSI v1.1 and Blaster were connected externally with the ProDrive internally. Yes, ZuluSCSI works from external term power ("Designed to be powered via SCSI termination power when provided by the host").

When I pulled the ProDrive, I added in an internal terminator that includes a hard drive connector to obtain power internal power from the internal hard drive connector.

 

[David Cook]

Thought it would be worth posting Blaster performance on the Quadra 605 (w/Bolle 128KB cache and 40 MHz overclock). Reached 4.5 MB/sec!

 

[jovianartifact]

What makes it "Blaster"? I saw the thred and thought "sound blaster".

 

[finkmac]

because it blasts the bits

 

[rabbitholecomputing]

What makes it "Blaster"? I saw the thred and thought "sound blaster".

Support for 16-bit CD audio emulation, for starters. The current optional DAC boards sell for $5

But as @finkmac also points out, it blasts the bits