It looks like disk controllers, which automatically update
disk address (DA) after completion of I/O, are expected to do
so even if there was no data transfer because of I/O errors.
I was studying RSX-11's Error Logger documentation and
examples are clearly offsetting disk addresses backwards
by one when I/O errors are reported by the controller.
Since once the controller has found the DA-specified sector,
the I/O begins regardless of the condition of the sector (bad
or good data) or ability to transfer the contents between the
disk and the memory. If an error occurs (NXM, for instance)
the operation would stop (with the error reported) at the end
of the sector. So if, for example, the bus address register
had a bad address from the get-go, no data would be able to
transfer at all, yet DA should still be updated with DA + 1
once the controller asserts the DONE bit.
This patch makes sure that DA is always advanced when I/O has
actually been commenced.
6a1b5685fd