Acorn Domesday AIV SCSI Boards - now free...

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simoni
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Acorn Domesday AIV SCSI Boards - now free...

Post by simoni » Sun Apr 29, 2018 2:17 pm

I've just finished recreating the original Acorn AIV SCSI Adapter card in KiCAD. This version is the same size, shape, layout, etc as the original card and should be a drop-in replacement for the original.

The design is untested at the moment but, since the routing follows the original board, there shouldn't be any issues. I'll order a print run of them shortly for testing. As the schematic is verified against the original board routing - the schematic is accurate (unlike the Acorn original schematic).

The board is designed to look just like the original when you place it in the Acorn Master - I saved the additional information for the bottom layer silk screen. The design is CC licensed Open Source Hardware, so you are welcome to use it, respin it, etc. Basically you can now make your own Domesday Master machine :) . This board is also useful if you want to back up a real SCSI drive. By connecting your original drive via the AIV card and a BeebSCSI on the external 1MHZ bus, you can back up drive contents with ease.

The KiCAD files are available on Github: https://github.com/simoninns/Acorn-AIV- ... apter-Card

/Simon
Acorn AIV SCSI Adapter Overview.jpg

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Re: Acorn Domesday AIV SCSI Boards - now free...

Post by ask_nz » Wed May 02, 2018 8:00 pm

Wow! That's awesome Simon.

Was it hard to do? Would love to learn this skill.

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Re: Acorn Domesday AIV SCSI Boards - now free...

Post by simoni » Wed May 02, 2018 8:17 pm

It takes time and practice to learn tools like KiCAD - but it's open-source and there are lots of tutorials around. This board took about two days to design (not including stripping down an original AIV board to use as a reference).

It's not an exact copy of the original as I have made some modifications to the layout and silk-screen (plus the placement of certain components is 'nudged' a little) but it should be very hard to tell from the original when installed - Except for the fact it says "Issue 2" on the silkscreen and copper :)

Shortly I'm going to order some of these boards and make one up to perform the final testing - I'm just waiting on some other designs I'm working on to be finished so I can order all the boards at once and save some postage cost.

Just seems crazy to me that people will pay 300 quid on ebay for an 'AIV Master' when this board (and the copro) are the only actual differences - and the copro is already covered by PiTubeDirect - so here is the other bit :)

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Re: Acorn Domesday AIV SCSI Boards - now free...

Post by ask_nz » Thu May 03, 2018 11:17 am

I remember you writing about the differences between the acorn SCSI host adapter and acorn video host adapter - is the Avi card the video adapter? Does it read/write all SCSI 1 drives?

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Re: Acorn Domesday AIV SCSI Boards - now free...

Post by simoni » Thu May 03, 2018 11:25 am

No, the AVI SCSI adapter is just SCSI. In Domesday all the analogue video mixing was performed by the VP415.

The board works with VFS and that will work with any SCSI drive ADFS can use (as VFS is really just a read-only version of ADFS). One note though is that VFS uses about 3 times slower DMA than ADFS (so the VP415 can keep up) - and that means access times are slower. Doesn't really make that much difference though.

If you want a really fast storage system that can connect to the internal 1MHz bus, then BeebSCSI is the answer :)

There are differences between the external Acorn SCSI adapter and the internal AIV board though (the logic is slightly different). There's a bunch of documentation about it on my website here: https://www.domesday86.com/?page_id=64

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Re: Acorn Domesday AIV SCSI Boards - now free...

Post by ask_nz » Thu May 03, 2018 11:39 am

So if I understand correctly the acorn SCSI host adapter is an externally connected card and the acorn Avi host adapter is the internal master card for doomsday?

Is the acorn SCSI host adapter the card in the acorn Winchester 110/130 device?
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Re: Acorn Domesday AIV SCSI Boards - now free...

Post by simoni » Thu May 03, 2018 11:44 am

Is the acorn SCSI host adapter the card in the acorn Winchester 110/130 device?
Yes, it's part of it. The Winchester was:

Acorn SCSI Card -> Adaptec ACB-4000 SCSI to MFM adapter -> MFM Hard drive

For the Domesday system the SCSI to Laserdisc part (equivalent to the ACB-4000) is built into the VP415.

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Re: Acorn Domesday AIV SCSI Boards - now free...

Post by ask_nz » Thu May 03, 2018 8:06 pm

So in theory - an acorn Winchester 110'130 system could drive a SCSI1 directly off the SCSI host Adapter Board? Would ADFS recognize it?
Reason for my question is that I have a broken Winchester 110 (failed MFM Drive), and I believe I have few early SCSI drives around somewhere. MFM drives are very hard to find.

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Re: Acorn Domesday AIV SCSI Boards - now free...

Post by simoni » Thu May 03, 2018 8:17 pm

So in theory - an acorn Winchester 110'130 system could drive a SCSI1 directly off the SCSI host Adapter Board?
Yes
Would ADFS recognize it?
Providing it supports 256 sectors, yes.

People are using things like SCSI2SD for exactly that.

Although you'd be better off putting a BeebSCSI in the Winchester box and getting 256Gb+ storage at a hundred times the speed :) You can make a whirring sounds and bounce nails off the table if you miss the nostalgic sounds :D

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Re: Acorn Domesday AIV SCSI Boards - now free...

Post by ask_nz » Fri May 04, 2018 6:25 am

:D

Yer - that’s what I miss - the sounds - lol

Daniel has just sent me 2 BeebSCSI boards so really looking forward to that - I’ll keep you posted on the sounds. :)

Keep me I mind for a AVI board - would love to try that too.

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Re: Acorn Domesday AIV SCSI Boards - now free...

Post by marcusjambler » Fri May 04, 2018 7:31 am

Great work Simon =D>

Registering my interest for a built board if and when they are available

Marcus

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Re: Acorn Domesday AIV SCSI Boards - now free...

Post by simoni » Fri May 04, 2018 7:37 am

I'll have to look into the possibility of building some; but it probably won't be cheap since it's all PTH components and the PCB is a very odd size as well as being big :) Files are all on Github though; so you are all welcome to spin your own in the meantime!

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Re: Acorn Domesday AIV SCSI Boards - now free...

Post by DutchAcorn » Fri May 04, 2018 8:21 am

ask_nz wrote::D

Yer - that’s what I miss - the sounds - lol ...
Use my recording! :D
Paul

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Re: Acorn Domesday AIV SCSI Boards - now free...

Post by simoni » Wed May 16, 2018 3:49 am

The AIV SCSI boards have now turned up. Eagle-eyed viewers will notice that I added a ground-plane to the underside of the board (to keep the signal shapes a little better). I didn't add this to the top-side though in order to keep the board's 'original' look when installed. I now have all the required components except the resistor network (that was more tricky to source, but I found a bunch on ebay - should arrive soon).

Soon I will build one up and test it in a real Domesday system to make sure it all works correctly. It looks like the mounting hole diameter may be a little small - easily fixed on both the physical boards and the KiCAD design. I'll update the Github repo as well.
AIV SCSI PCB.jpg

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Re: Acorn Domesday AIV SCSI Boards - now free...

Post by ask_nz » Sat May 26, 2018 4:32 am

Can't wait to see this :D =D> =D> =D>

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Re: Acorn Domesday AIV SCSI Boards - now free...

Post by simoni » Sat May 26, 2018 5:34 am

Can't wait to see this
The 'test' build is almost complete; just waiting on the resistor network to be delivered (it's a bit of an odd component).

This board is just to make sure everything is ok - for the real versions I'm going to try and find some grey cable and some more 'authentic' looking capacitors :)

IMG_20180526_073003.jpg

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Re: Acorn Domesday AIV SCSI Boards - now free...

Post by ask_nz » Mon Jun 18, 2018 8:48 pm

Hi Simon, How are things progressing with this project?

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Re: Acorn Domesday AIV SCSI Boards - now free...

Post by simoni » Mon Jun 18, 2018 8:53 pm

I'm still waiting on the resistor networks. I found some via eBay, but they have been stuck in customs for over three weeks... I sent some emails yesterday to the seller and the postal company and I'm waiting for a response. Frustrating, but there you go. I've not abandoned it though :)

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Re: Acorn Domesday AIV SCSI Boards - now free...

Post by dominicbeesley » Mon Jun 18, 2018 10:05 pm

I've got a pile of full height SCSI drives to play with soon. Does this plug into the Pl12 connector? Would one of these boards be adaptable to work in a model B by hooking up to the 1MHz bus with a simple address decoder, or maybe I'd be better making something from scratch for the model B?

D

PS: It looks very good!
Last edited by dominicbeesley on Mon Jun 18, 2018 10:06 pm, edited 1 time in total.

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Re: Acorn Domesday AIV SCSI Boards - now free...

Post by simoni » Tue Jun 19, 2018 3:58 am

The board is a replica of the Acorn AIV SCSI adapter. It's designed to connect to PL12 and be mounted inside the BBC Master (if you look up the AIV SCSI board original - this board does exactly the same).

The logic of the AIV SCSI adapter and the original BBC 1MHz bus adapter is not the same, so the board cannot be used on the external 1MHz bus. Actually, the two buses are not even the same electrically. PL12 is CMOS and the external bus is TTL. I posted a link above to the domesday86 website where all of the details (for both types of SCSI adapter) are described.

You can connect a SCSI-1 harddrive to the internal bus using this card though (on a Master).

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Re: Acorn Domesday AIV SCSI Boards - now free...

Post by dominicbeesley » Tue Jun 19, 2018 11:17 am

Thanks Simoni,

I'd not clocked that PL12 was CMOS, I was hoping a '138 might be enough to interface to the 1MHz bus.

It looks like yet another slow burn project for me, first I need to find some decent information on how the low level bus protocol works as it doesn't look as straightforward as IDE! Does anyone know of a good place to start looking. Most of the specs seem still to be shrouded in mystery and behind firewalls. I seem to recall the actual bus protocol being in a friend's electronic engineering textbook when I was at uni and I helped him with a project...

D

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Re: Acorn Domesday AIV SCSI Boards - now free...

Post by simoni » Tue Jun 19, 2018 11:27 am

As part of the Domesday86 project I've produced extensive documentation on the SCSI-1 protocol used by ADFS and VFS. There is also BeebSCSI which emulates both SCSI-1 hard drives and the VP415 LaserVision player used by Domesday. BeebSCSI also includes a verilog implementation of both the internal AIV SCSI adapter and the external 1MHz SCSI adapter.

The whole project is open-source and open-hardware, so you can access every detail of the implementation along with the technical documentation covering every SCSI command and the Acorn specifics. BeebSCSI also acts as a SCSI protocol analyser; you can hook it up to a serial adapter and it will dump everything about the SCSI conversation in human-readable format. It will even hex-dump the transferred data blocks if you ask it too.

I'd argue that, rather than there being 'no decent information available', it's one of the most documented aspects of the BBC's interaction with a specific hardware device :)

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Re: Acorn Domesday AIV SCSI Boards - now free...

Post by dominicbeesley » Tue Jun 19, 2018 11:48 am

I had a look at the https://www.domesday86.com/?page_id=64 documentation for the interface which is great. By no "decent information" I meant proper standards documentation for parallel SCSI-1 interface, not a criticism of what you have done.

What I was hoping for is something that lays out in detail all bus signals, the way transactions work etc, preferably with state/timing diagrams etc. The description above is great if you understand the way SCSI transactions work...which I don't yet. I'll try and get some time to work through the CPLD sourcecode and ADFS ROM

Thanks

dom

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Re: Acorn Domesday AIV SCSI Boards - now free...

Post by simoni » Tue Jun 19, 2018 1:27 pm

The SCSI-1 interface implemented by ADFS is really SASI. It was made at a point where SASI was being transformed into SCSI. It's probably why little original documentation exists. The Adaptec ACB-4000 documentation (which is widely available) contains the specific implementation used by Acorn (as it was the hardware used by the original Winchester products made by Acorn).

The SASI interface also has a specification that covers the whole range of possible implementations (most of which is not supported by ADFS) along with the electrical specification for the bus. I've attached a zip of the original SASI spec in case it's useful. The source code to BeebSCSI is far more understandable though in terms of real-life implementation.
Attachments
X3T9.3_185_RevE_SASI_Apr82.zip
SASI Specification
(2.13 MiB) Downloaded 2 times

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Re: Acorn Domesday AIV SCSI Boards - now free...

Post by dominicbeesley » Tue Jun 19, 2018 2:49 pm

Aha, thanks Simon, that's very helpful!

That's given me the leg up I needed. One final question before I print a load of this out to read in bed. Am i right then in thinking that the Beeb SCSI/SASI interface doesn't do the "arbitration" step and that it is always the initiator, or have I got hold of the wrong end of the stick?

D

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Re: Acorn Domesday AIV SCSI Boards - now free...

Post by simoni » Tue Jun 19, 2018 3:06 pm

There's no arbitration of the bus in ADFS. The host ID is always 1 and it supports 1 target with 4 LUNs (8 LUNs under VFS).

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