SCSI / SCSI II adapaters?

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dominicbeesley
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SCSI / SCSI II adapaters?

Post by dominicbeesley » Mon Jul 09, 2018 9:38 am

I have been following the Domesday SCSI threads with interest and was wondering what other SASI/SCSI/2 adapters there were for the Beeb/Master. I got a little carried away and bought a SCSI disk (actually SCSI 2 which I'm not sure would even work with the original Master Domesday adapter?). I also have some Z53C8003 chips which look like with a small amount of glue logic would quite quickly make a SCSI 2 adapter - there would then be the _very_ slow process of wading through the datasheets and trying to port a filing system...

This looks like another slow burn project but I'd love to have a _real_ desk shaker SCSI HD on my beeb/6809 machine

D
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simoni
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Re: SCSI / SCSI II adapaters?

Post by simoni » Tue Jul 10, 2018 9:26 am

Well, anything is possible with some work :) The main issue with SCSI-2 (and, in fact, some SCSI-1) is the sector size is often 512 bytes rather than the 256 bytes used by the original ADFS. Unless the drive controller uses 256 it's going to be tough to make it work on a Beeb (although the Master could be more readily adapted since it has better use of shadow-RAM for filing system workspace).

I say 'drive controller' rather than 'drive' as the original Acorn solution had a 1MHz bus to SCSI adapter and then a SCSI to 'drive' adapter (the ACB-4000 from Adaptec). Later hard drives had the SCSI part built in. The BeebSCSI project (part of Domesday86) has both elements - a CPLD implements the host adapter and an AVR provides the SCSI. I took a lot of care to make the system representative of the original (the interface between the CPLD and AVR is actually SCSI-1 running at 3.3Vs). There should be a lot to be gained from looking at both the Verilog and C code (all of which is open-source). You could even modify it to support 512 byte sectors which would give you a good base-platform on which to develop the required filesystem support for more 'modern' SCSI-2 drives.

As a faster route, you could always interface a big vibration motor to the BeebSCSI's microcontroller and emulate the desk-shaking experience of the original :D

dominicbeesley
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Re: SCSI / SCSI II adapaters?

Post by dominicbeesley » Tue Jul 10, 2018 9:54 am

Thanks Simoni,

I'll take a look at your beebSCSI code, I'd not realised it contained an actual SCSI bus that should be very interesting.

The drive I've got is a Micropolis 1578, it has its own controller but that seems to support various sector sizes including 256 bytes, though it will probably require a re-format which I suspect will be non-trivial. The first thing is going to be to dig out a RiscPC, I'm sure I had one somewhere with a SCSI (2?) card that ran a syquest. Hopefully I'll be able to format the drive on that as I'd like to at least start with something "known good"!

Back in the mists of time I ran SCSI disks on 386 and 486 PC's and the RiscPC but I never really got into anything low-level. The whole spec seems over-facing so I doubt that I'll get anywhere very quickly!

No doubt there will be lots of questions when I start digging into the ADFS code. The 53c8xxx chips seem to do quite a bit of work but SCSI2 looks a bit more complex than SASI so it's may be a squeeze to get all the hardware code shoehorned in to the existing FS ROMs

D

RobC
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Re: SCSI / SCSI II adapaters?

Post by RobC » Tue Jul 10, 2018 11:11 am

I have an original Oak SCSI card that's hooked up to a more modern Seagate drive (2GB I think). I found that some Seagate drives can be persuaded to switch to 256-byte sectors - I did this by issuing the relevant SWIs on my RiscPC. There are some threads on here about it somewhere.

I also have an Akhter SCSI card that's connected to an Adaptec board and a 20MB ST506 drive.

I can dig them out if you want photos...

dominicbeesley
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Re: SCSI / SCSI II adapaters?

Post by dominicbeesley » Tue Jul 10, 2018 12:44 pm

Thanks Rob,

So are both the Akhter and Oak Beeb 1MHz bus cards, I've been searching around for info but not finding much

Were all the host adaptors much of a muchness i.e. did they all have the same hardware API to the beeb? I might ditch the 53c8000 idea and just make a SASI interface...

D

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simoni
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Re: SCSI / SCSI II adapaters?

Post by simoni » Tue Jul 10, 2018 1:05 pm

The host adapter cards are specific to ADFS so the logic is fixed. The only variance is the external card and the internal (VFS) adapter for the Master (as the glue-logic is different).

Schematics and a description of the glue-logic design is available here: https://www.domesday86.com/?page_id=64

You can also download and view my AIV SCSI card remake (in KiCad) here: https://github.com/simoninns/Acorn-AIV- ... apter-Card

dominicbeesley
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Re: SCSI / SCSI II adapaters?

Post by dominicbeesley » Mon Jul 30, 2018 9:28 pm

Thanks Simoni, RobC,

I decided to take the plunge and have a go at a SCSI 2* board. I've made a quick start today (between house painting, packing, moving). I've based this round a z53c8003 chip. I've no idea how far I will get with this but it looks interesting, well, to me at least...

I didn't get a picture of the board before I packed it for moving but here's the schematic...
scis2.png
I've wired up the 1MHz bus, glue logic, z53c80 today and it seems to work ok, IRQ/NMI not tested at all as I have run out of 74LS05's

I'm going to start looking at ADFS sources I'm guessing that the v150.zip on JGH's site looks to be the best starting point? It appears that this has an option to compile all the various IDE/SCSI/MMC BBC/Elk/Master versions - do they all work?

I'll probably be restricted to just one machine for the next year or so due to space limits and that will likely be a BBC B...

D

* I doubt this will be a full SCSI II implementation but will hopefully/maybe work with newer stuff?

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Re: SCSI / SCSI II adapaters?

Post by dominicbeesley » Wed Aug 01, 2018 8:54 pm

I can't wait to get the SCSI pins wired up and have a go at programming the thing...
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dominicbeesley
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Re: SCSI / SCSI II adapaters?

Post by dominicbeesley » Sat Aug 04, 2018 4:44 pm

After a couple of hours grabbed here and there I've got it doing some very basic and no doubt buggy talking across the bus. Here it's run the "inquiry" command on the hard drive.

This seems to take a lot of code...
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