Zorro DMA vs Accel. DMA: Cyberscsi vs A4091

[Jose]

So, I was thinking:
1- The onboard scsi of the A4000T and the A4091 scsi controlers are reported to be faster then the Cyberscsi module of the Cyberstorm MkII or other processor card add ons.
2- Yet the 4091 uses the ZIII bus, which means that it will be in direct competition with say a Gfx card if you want to do dma transfers from accelerator memory to video memory (or is that not possible ?).

This means that if one wants to run a high frame rate / high res / true color anim, a Cyberscsi based system will still be faster since it won't be using the ZIII bus at all.

Is this correct, or no difference in practice ?

[Zac67]

The Mk-III and PPC Cyberstorms use UW SCSI, so they should be considerably faster than an A4091 or A4000T - possibly up to 40 MB/s. Otherwise you seem to be right, but Fast SCSI at 10 MB/s plus the same speed to video might not be fast enough to overload Z III - I've got ~20 MB/s in the back of my head with a Rev 7 Buster. If the more modern SCSI adaptors actually run that high the gfx card is your next bottleneck...

[Jose]

This is a big mess...
PIV ZIII transfers are around 14MB/s IIRC, Cybervision64 16MB/s and the 3d model of it 6MB/s.
I'm thinking about keeping the PIV so it should be around 20MB ZIII bandwidth with the disk transfers (not that there will probably be any software taking advantage of it but it would be fun to program for....
On the other hand, I've been considering selling the 4000T for a while, but since my MKII (recently bought from eBay) doesn't have the Cyberscsi module I don't know.
Specially since the MKII is reported to not overclock well with the scsi module.
I've seen an old post by Pasha saying there is a version of the scsi module that tolerates overclocking but I've yet to see a report with an 80Mhz MkII with working scsi. The A4000T would allow that easily, getting an 4091 for the 4000D will make it too hot and with no space inside...
But then A4091 controler (same one on the 4000T) doesn't work with a DMA enabled Deneb...

Decisions, anyone seen a working Cyberscsi module at 80Mhz ?

[doctorq]

I've seen an old post by Pasha saying there is a version of the scsi module that tolerates overclocking but I've yet to see a report with an 80Mhz MkII with working scsi.

IIRC Pasha stated that SCSI modules containing the glogic chip could be overclocked, whereas the SCSI modules with the Symbios chip couldn't. I have a Cyber SCSI MKII with glogic chip, and when I tried to overclock, I couldn't get it to start up with even a 60 MHz oscillator. I doubt that you will find someone with a MKII running at 80 MHz with the SCSI module running as well.

[Jose]

@doctorq

Thanks a lot for posting that, looks like I'll have to use the 4000T or get an A4091. Shame that it won't work with a Deneb...

[Damion]

I suppose it depends how much bandwidth can be utilized before something else chokes. There's barely a 1 FPS difference between my Z2 and Z3 machines in Quake benchmarks, so 20 MB/s for Z3 should be enough. I imagine (non-expert guess here) the PIV or CPU would become a bottleneck before the Z3 bus.

[Jose]

@doctorq
Have you tried just various oscillators ? It could be a timing issue. Also, do you have 70ns ram ? If so ram could be the limiting factor.

@Damion
Sounds interesting (Z2 vs Z3), but you didn't say what video cards / processor cards you have on them...

[doctorq]

@doctorq
Have you tried just various oscillators ? It could be a timing issue. Also, do you have 70ns ram ? If so ram could be the limiting factor.

It was just a very quick test, without any kind of tweaking at all. All I did was to replace the 50 MHz oscillator with a 66 MHz, 60 MHz and a 56 MHz. It was just with the 56 MHz oscillator I saw some sign of life. Ram was rated at 60 ns.

As said, it was just a quick test, and some tweaking may have gotten the card to boot at higher speeds. Even at 60 ns, I still suspect the ram could have something to do with it due to the build quality.

I never have gotten around to mess with it some more due to lack of time, others might succesfully have overclocked their CSMK2. I still have my doubt about succesfully overclocking to above 66 MHz with fully and stable working SCSI as well.

[Damion]

@Damion
Sounds interesting (Z2 vs Z3), but you didn't say what video cards / processor cards you have on them...

The A2K has a TekMagic '060/PIV, the A3K also an '060/PIV. I swapped the same CF hard drive between the machines for testing. Regardless of the screen resolution or other settings, Quake was .5 - 1 FPS faster on the Z3 machine. With a 10MHz advantage, the A2K was 1.5 FPS faster. (Didn't overclock the MKII yet.) A1200/AGA was 2 FPS faster than the A2K, but with a 20 MHz advantage (haven't yet tested them at the same clock).

In graphics benchmarks, the A2K/A3K were roughly equal up to 1024x768x16. Only switching to high-res true color modes was the Z3 machine a bit faster, for example, WB backdrops would take a bit longer to draw on the A2K. Writes to the PIV hit the Z2 theoretical maximum (according to Thomas Wenzel's CgxBenchmark), which probably helps.

No difference with RTG demos, either. Running Lightshaft with the -fps tag, they are about equal.

[Zac67]

But then A4091 controler (same one on the 4000T) doesn't work with a DMA enabled Deneb...

... which is neither the fault of the A4091 nor the Deneb's. Unfortunately even the last Buster 11 only supports a single DMA device.

[Jose]

@Zac67

I could put back a Buster9, which supports more than 1 DMA device but it doesn't work with the A4091 (it's what they say but I also remember having an A4091 working with Buster9 before that and it worked fine!?) and my Busters are both rev. 11 and soldered on both machines:(. Funny, I payed Castellen to solder the rev. 11 in the 4000D and I think he asked me if I wanted to put a socket, to which I said no, for what...

The only other solution would be getting a FastLane or a 4098 from GVP. I don't know if the GVP works with Buster9 but the FastLane does. On the other hand Fastlanes cost a fortune on eBay.

[Zac67]

According to Dave Haynie, the rev 9 is flawed and is likely to cause trouble (from BBoAH):
   The Level II part (about twice as many gates) was out in two revisions; Rev 9, which initially shipped with the A4000, and Rev 11, which is the best you'll ever get. The Rev 9 part has two bugs that can cause problems with Zorro III cards. One can affect some kinds of bus slave cards, it depends on the card design. This is due to a small flaw in a synchronizer stage in the Level II chip (Level II runs a slightly faster bus protocol than Level I, and also supports burst). The other is a flaw in the Zorro III bus arbiter -- there's a small window in which a Zorro III slave cycle just starting can confuse a bus registration command, locking the bus. Rev 11 solves both problems, so you need it for DMA devices. The Rev 9 problems were fairly well qualified, so you have some devices that offered work-arounds. I didn't for the A4091 -- at the time, C= probably wouldn't have let me do the Rev 11 chip if the A4091 could have worked at all in existing A4000s.

As I understand it, an A4091 wouldn't work reliably with a Buster 9 but you might have been lucky.

[Ami_GFX]

@Zac67


The only other solution would be getting a FastLane or a 4098 from GVP. I don't know if the GVP works with Buster9 but the FastLane does. On the other hand Fastlanes cost a fortune on eBay.

I just replaced the GVP 4008 in my rev 9 buster A4000 with a Fastlane. The 4008 worked flawlessly. The 4008 is Zorro II and rev 9 busters work fine with Zorro II cards. The Fastlane cost me $100 and another $30 for the memory. I bought it for the memory expansion and it didn't cost me so much, especially compared to what even an 040 accelerator would cost me that would give me a decent amount of memory. The faster SCSI is nice but all I use SCSI for on my A4000 is an external ZIP drive which lets me pass files back and forth between Winuae and my real Amigas.

[Jose]

@Ami_GFX

I'd say get one of those SCSI to IDE adapters, they're cheaper nowdays and make the HD so much faster than IDE and specially with small overhead.
Ah, ok 4008, I was think about the 4098...

[Jose]

BTW, a FastLane or 4098 or DKB, whatever, probably would have problems too, some of them might be DMA masters. Anyone has a list of cards which are DMA masters, must be a small one...