Cumana SCSI interface in A5000

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Orkie
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Cumana SCSI interface in A5000

Post by Orkie » Tue Oct 13, 2020 5:14 pm

Hi,

I picked up a Cumana SCSI interface (rev 4) but when I connect it to my A5000, the machine won't boot (just hangs at a black screen). I've tried all the slots, and have tried a different podule in those slots which appears to work fine.

I tried removing the EPROM from the SCSI card, and the machine boots so it would appear not to be that something is shorted on the card for example (it looks very clean, no sign of damage). Obviously I can't use it without any of the drivers though!

It has a label on the ROM saying "Cumana C40E SCSIFS/CDFS 1.19 2.21" and I'm wondering if this version may be incompatible with the machine/RISC OS 3.10? I've dumped it (several times - definitely getting the same data out each time), and can see on my Linux machine with strings that there is at least something meaningful there. Have tried writing the same image to another 27C512 on the off chance that the chip was a bit dodgy but same result.

Does anybody have any ideas, or a known good dump of a different version of the ROM which definitely works with an A5000?

Many thanks

philb
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Re: Cumana SCSI interface in A5000

Post by philb » Tue Oct 13, 2020 5:28 pm

I have a Cumana SCSI in my A5000. It's at the office, but I can dump the ROM for you tomorrow if you need it.

Orkie
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Re: Cumana SCSI interface in A5000

Post by Orkie » Tue Oct 13, 2020 5:34 pm

If you don't mind, it'd be very much appreciated - worth a shot to rule out a software issue!

carcher
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Re: Cumana SCSI interface in A5000

Post by carcher » Tue Oct 13, 2020 10:24 pm

Try fitting a SCSI terminator to the card (internal or external) - you probably don't need a SCSI device connected just termination. I had a similar issue with a Cumana SCSI2 card which I believed to be faulty. It worked perfectly as soo as I terminated the SCSI bus.

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BeebMaster
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Re: Cumana SCSI interface in A5000

Post by BeebMaster » Wed Oct 14, 2020 1:56 pm

I've got 2.10 in my Cumana SCSI podule, which definitely works in my A5000:

Image

I think I can only dump ROMs up to 27256 though in my programmer.

What other podules do you have? My Cumana podule now lives in my RISC PC 700, but I recently discovered that it's incompatible with the IanS Econet Module Podule, just get Address exception and other errors preventing a boot.
Image

philb
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Re: Cumana SCSI interface in A5000

Post by philb » Wed Oct 14, 2020 3:52 pm

Irritatingly it turns out that I had swapped the Cumana SCSI for a different one at some point and a quick search of the premises didn't turn up the Cumana. It must be there somewhere but I have rather a lot of boxes of circuit boards at the moment. I will look again next time I'm there if you haven't managed to get a copy of the ROM elsewhere in the meantime.

BeebMaster, if your podule is in a working computer then I think you should be able to dump the ROM contents that way. Not that I remember exactly how to do it off the top of my head, and my PRMs are downstairs, but I think there is a Podule SWI to read from the ROM area if there isn't a *-command to do it.

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BeebMaster
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Re: Cumana SCSI interface in A5000

Post by BeebMaster » Wed Oct 14, 2020 7:24 pm

That would certainly be good to know. I wonder if it is as simple as just doing a *SAVE like you can with ROM modules.

Anyhow, it's not exactly in a working machine...it's inside the RISC PC, but not actually connected to the backplane because of the conflict problem mentioned before, and I don't fancy taking the machine apart again. One man's simple disassembly is another BeebMaster's irreparable destruction.
Image

philpem
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Re: Cumana SCSI interface in A5000

Post by philpem » Thu Oct 15, 2020 11:18 am

BeebMaster wrote:
Wed Oct 14, 2020 7:24 pm
That would certainly be good to know. I wonder if it is as simple as just doing a *SAVE like you can with ROM modules.

Anyhow, it's not exactly in a working machine...it's inside the RISC PC, but not actually connected to the backplane because of the conflict problem mentioned before, and I don't fancy taking the machine apart again. One man's simple disassembly is another BeebMaster's irreparable destruction.
Not quite. You can dump the Podule Loader and use that to dump the rest of the ROM, but that's the ROM "as the computer sees it". What's in the EPROM may not be the same, depending on the banking scheme, and will be missing the Loader and ROM header.

Often the Podule Loader applies an offset so that RISC OS doesn't 'see' the first header when it tries to load the modules.

The long way round is to grab the Podule loader, reverse engineer it to find out how the ROM banking works, then write a BBC BASIC program to duplicate its function. That should allow you to read any address in ROM. That still doesn't help with the banking scheme and physical ROM wiring, but will give you the modules and any other data loaded into the ROM.

Generally it's easier to pull the EPROM and use an EPROM programmer... I usually only go down the "use the loader" route if I want to extract modules for disassembly or rebuilding new ROMs.

Cheers
Phil.

philb
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Re: Cumana SCSI interface in A5000

Post by philb » Thu Oct 15, 2020 12:03 pm

Oh yes, right. I need to go over to the office again tomorrow so I'll have another look for the Cumana card at that time.

Orkie
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Re: Cumana SCSI interface in A5000

Post by Orkie » Sun Oct 18, 2020 11:00 am

Thanks all, lack of termination was indeed the issue - it'd never occurred to me that the module would just hang without that!

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