LVL DOS Error

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maxstokeman
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LVL DOS Error

Postby maxstokeman » Tue Oct 31, 2017 1:16 pm

Hi. My first post here. I have inherited a BBC Model B from my father in law. It has LVL DOS which I understand is quite rare and for which I can't find any manuals on the web. There is a thread elsewhere in this forum about the lack of documentation for this DOS. I am getting an error "Floppy Fault - 7C at 00/00 Ready Only? Density?" when I use *. to get the catalogue. I can't find any information on this fault online. Can anyone help? Interestingly, I get the error whether or not the disc drive is switched on or not and with or without a disc in the drive. Screen shots attached. Thanks!
Attachments
IMG_6904.JPG
IMG_6903.JPG

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Pernod
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Re: LVL DOS Error

Postby Pernod » Tue Oct 31, 2017 7:58 pm

Unfortunately there's is almost nothing known about LVL Dos, no manuals have ever been found. It really needs someone to disassemble the ROM to determine how it works.

I did find a review in Acorn User Feb.84, which states:
Switching between double and single density is extremely simple: an extension of the "DRIVE command allows the user to state either 'S' or 'D' to select the density.

So a

Code: Select all

*DRIVE 0 S
may help.
It also suggests it may be 40 track only!

Would you be able to provide some quality photos of the board?
- Nigel

BBC Model B, ATPL Sidewise, Acorn Speech, 2xWatford Floppy Drives, AMX Mouse, Viglen case, etc.

maxstokeman
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Re: LVL DOS Error

Postby maxstokeman » Tue Oct 31, 2017 10:10 pm

By some miracle, today I found the original manual for the LVL DOS! I'll get this scanned into a PDF and share with the forum. I can take some photo's of the board yes and post here. In the manual there is a list of error codes (on the last page) but the error code I'm getting (7C) isn't listed, so that's not too much help.

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BeebMaster
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Re: LVL DOS Error

Postby BeebMaster » Wed Nov 01, 2017 8:48 pm

Oh right. I don't think I knew it was missing. I have several LVL DOS related items, all in storage, including a non-working BBC B with LVL DOS board, which looks to have quite a few chips missing:
LVLBeeb18.jpg
LVLBeeb19.jpg

Also from the same vintage

" Box & Manuals & Misc EPROMs & ICs inc “LVL Super DOS” & “LVL DDOS 0.9F” "

and from an earlier time "LVL Disc System User Guide"

I'll have to try to retrieve it all and get the ROMs imaged and the documentation scanned.
Image

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jgharston
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Re: LVL DOS Error

Postby jgharston » Wed Nov 01, 2017 9:10 pm

maxstokeman wrote:By some miracle, today I found the original manual for the LVL DOS! I'll get this scanned into a PDF and share with the forum. I can take some photo's of the board yes and post here. In the manual there is a list of error codes (on the last page) but the error code I'm getting (7C) isn't listed, so that's not too much help.

If the error code is the result of reading the status register (and there's only one status-type register on the 1797), then it's saying: Write Protect and Write Fault and Record Not Found and CRC Error and Lost Data. The only thing it's not reporting is Not Ready.

Are the error codes in the manual listed as something like:
&04: Lost Data
&08: CRC Error
&10: Sector Not Found
&20: Write Error
?

Code: Select all

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

maxstokeman
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Re: LVL DOS Error

Postby maxstokeman » Sun Nov 05, 2017 7:06 pm

Yes, those are pretty much spot on. I've uploaded a scanned version of the LVL DOS Manual that I have for general consumption.
Attachments
LVL DOS Manual Small (2017 11 05) v1.pdf
(1.45 MiB) Downloaded 14 times

maxstokeman
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Re: LVL DOS Error

Postby maxstokeman » Sun Nov 05, 2017 7:07 pm

So, if it's reporting "Write Protect and Write Fault and Record Not Found and CRC Error and Lost Data" how can I resolve that? I'm not a BBC wizard and I don't have a strong understanding of LVL DOS, DFS etc. Thanks.

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Pernod
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Re: LVL DOS Error

Postby Pernod » Sun Nov 05, 2017 8:33 pm

BeebMaster wrote:Oh right. I don't think I knew it was missing. I have several LVL DOS related items, all in storage, including a non-working BBC B with LVL DOS board, which looks to have quite a few chips missing:

Thanks for the photos, much better quality than those at http://chrisacorns.computinghistory.org ... e_FDC.html. The empty sockets would be for the 8271 and supporting chips but seems this was never implemented. Would you agree the 6522 is only moved to the board for support, and not used by the FDC?
- Nigel

BBC Model B, ATPL Sidewise, Acorn Speech, 2xWatford Floppy Drives, AMX Mouse, Viglen case, etc.

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jgharston
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Re: LVL DOS Error

Postby jgharston » Sun Nov 05, 2017 9:54 pm

maxstokeman wrote:So, if it's reporting "Write Protect and Write Fault and Record Not Found and CRC Error and Lost Data" how can I resolve that? I'm not a BBC wizard and I don't have a strong understanding of LVL DOS, DFS etc. Thanks.

The status register is a bitmap where only one bit is meant to be set. If more than one is being set then something odd is happening with the hardware to confuse the controller.

Code: Select all

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

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BeebMaster
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Re: LVL DOS Error

Postby BeebMaster » Mon Nov 06, 2017 11:37 pm

Pernod wrote:
BeebMaster wrote:Oh right. I don't think I knew it was missing. I have several LVL DOS related items, all in storage, including a non-working BBC B with LVL DOS board, which looks to have quite a few chips missing:

Thanks for the photos, much better quality than those at http://chrisacorns.computinghistory.org ... e_FDC.html. The empty sockets would be for the 8271 and supporting chips but seems this was never implemented. Would you agree the 6522 is only moved to the board for support, and not used by the FDC?

Looks like it, although the Beeb it was in doesn't work so I haven't been able to test it yet.
Image


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