Atom DOS

discussion of games, software, hardware & emulators relating to the Acorn Atom and Acorn System machines.
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Prime
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Atom DOS

Post by Prime » Sun Sep 19, 2010 5:52 pm

Hi all,

Now I have a working Atom disk drive, I'va had a play, and it seems to support the *drive command in much the same way as Beeb DFS, though the manual seems to make no mention of it ! And it does seem to support multiple drives, though as far as I know Acorn only ever supplied single drive systems.

So I descided to have a play, and attached a 3.5" drive to it as drive 1/3, trying to format this gets all the way through the format stage but always falls over verifying after it displays track &14 (20), I suspect this is the point that precomp is enabled....

I do seem to remember that there where problems with DFS 0.90 (8271) with 3.5" drives, does anyone have the details of what patches where needed to make it work.

Also does anyone happen to have a dissasembily of the Atom DOS rom ?

Cheers.

Phill.

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MartinB
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Re: Atom DOS

Post by MartinB » Sun Sep 19, 2010 7:44 pm

Prime wrote:I do seem to remember that there where problems with DFS 0.90 (8271) with 3.5" drives, does anyone have the details of what patches where needed to make it work.
Sprow clearly explains the 8271 issue here and as he briefly mentions, the DFS patch just keeps re-trying the drive command if a 'Drive not Ready' error is reported. What type of FDC chip does the atom use?

Prime
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Re: Atom DOS

Post by Prime » Sun Sep 19, 2010 9:45 pm

MartinB wrote:
Prime wrote:I do seem to remember that there where problems with DFS 0.90 (8271) with 3.5" drives, does anyone have the details of what patches where needed to make it work.
Sprow clearly explains the 8271 issue here and as he briefly mentions, the DFS patch just keeps re-trying the drive command if a 'Drive not Ready' error is reported. What type of FDC chip does the atom use?
It also uses the 8271, actually there's quite a bit of similarity between the atom disk controler circuit and that in the Beeb (perhaps unsupprisingly), I think also the formats are pretty similar, as I managed to read data off an Atom dos disk image with the Beeb DFS emulation under mess, must try on a real machine at some point.....

Humm having had a look at Sprow's site, it seems the problem is the circuit to fake the drive ready signal, now if I had a 3.5" drive that actually supplied the ready signal (I have some that I modified for Spectrum +3/Amstrad use which required ready on pin 34), perhaps I could bypass the fakeup circuit and read ready direct from the drive.....humm I might try that.

Cheers.

Phill.

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MartinB
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Re: Atom DOS

Post by MartinB » Sun Sep 19, 2010 11:45 pm

This might be me misreading what you've just said but it's not a drive ready issue as such, it's the missing index pulse after a head step that causes the problem. Is that your understanding?

Prime
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Re: Atom DOS

Post by Prime » Mon Sep 20, 2010 1:11 pm

MartinB wrote:This might be me misreading what you've just said but it's not a drive ready issue as such, it's the missing index pulse after a head step that causes the problem. Is that your understanding?
Humm well the impression I got was that the missing index pulse was causing the ready fake circuit to timeout and cause the drive ready signal to go high.

Specifically :

"What this means is that there are is a timeout on the ready signals of 1.9Hz (about 520ms). As a 3.5" drive spins at 300 revolutions per minute (200ms per revolution) a missing index pulse causes the latches to time out and tell the 8271 that the drive is not ready. "

So asuming that a drive that is wired to output the ready signal was connected with suitable logic to gate the ready signal to the correct pin of the 8271, I would have thought the 8271 would then see the next index pulse and continue to be able to access the drive.

I'll do some experements tonight and see if that solves the problem....might actually use one of my spare beeb boards, as they use the same logic, but I have more of them than AtomDOS boards (1) :)

Cheers,

Phill.

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MartinB
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Re: Atom DOS

Post by MartinB » Mon Sep 20, 2010 4:04 pm

Ok Phill, understood 8). I thought you were somehow just going to tie the drive to permanently 'ready' which sounded like trouble.

Prime
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Re: Atom DOS

Post by Prime » Mon Sep 20, 2010 6:16 pm

MartinB wrote:Ok Phill, understood 8). I thought you were somehow just going to tie the drive to permanently 'ready' which sounded like trouble.
Indeed that would be trouble :)

Anyway feeding the ready signal from the drive and bypassing IC6 on the Atom dos board seems to have done the trick, I can now format and use a 3.5" disk, though obviously only 40 track.

Same trick would proably work on the beeb too.

Cheers.

Phill.

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BeebMaster
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Re: Atom DOS

Post by BeebMaster » Tue Sep 21, 2010 1:33 pm

Prime wrote: It also uses the 8271, actually there's quite a bit of similarity between the atom disk controler circuit and that in the Beeb (perhaps unsupprisingly), I think also the formats are pretty similar, as I managed to read data off an Atom dos disk image with the Beeb DFS emulation under mess, must try on a real machine at some point.....
There's a BASIC utility on the BBC Model B Welcome Disc called "DCONV" which will "upgrade" a pre-BBC micro Acorn-format disc to BBC DFS. If you work that through, it will probably give you all the differences between DFS format and the Atom/System disc format.
Image

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jgharston
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Re: Atom DOS

Post by jgharston » Wed Sep 22, 2010 2:22 pm

BeebMaster wrote:There's a BASIC utility on the BBC Model B Welcome Disc called "DCONV" which will "upgrade" a pre-BBC micro Atom-format disc to BBC DFS. If you work that through, it will probably give you all the differences between DFS format and the Atom/System disc format.
The difference is that Atom DOS puts all files in directory " " (space) and has 16-bit load/exec addresses. The conversion program puts all files in the "$" directory and clears b16-b17 of the load/exec address.

Code: Select all

$ bbcbasic
PDP11 BBC BASIC IV Version 0.25
(C) Copyright J.G.Harston 1989,2005-2015
>_

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