Re: DMA Errors - weird fix?

From: Oliver Skelton <>
Date: Fri, 28 Nov 1997 19:20:03 +0000

I only realised the other day that I get corruption when writing to scsi
in TC mode (without Nemesis on).

It may be that it started with the change to HDDRIVER 7, or the
temporary experiment with a 1kohm resistor in parallel with the 100 ohm
resistor in the DMA patch - I hope to test that soon.

However, what intrigued me was the nature of the corruption.
FAT1 not equal FAT2
FAT and directories and I think files, all with a particular pattern of
corruption at random places.

>From memory:
14 bytes are shifted +16 bytes in position in the file but I think 2
bytes are somehow skipped.
Then alternate runs of 16 bytes are exchanged.
At some point an extra 2 bytes is inserted and the corruption ends.

The gist of it is that the data can be patched up in FAT and directories
because you can see what needs to be swapped back to where... but damage
within files is (depending on file type) much harder to repair. Thank
god for backups :-)

Received on fr. nov. 28 1997 - 22:16:00 CET

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