4.2 disk driver bug (and fix!)

[Jeff Gilliam]

There seems to be some confusion regarding the problems the 4.2 hp disk
driver has when used with Systems Industries controllers.  The difficulty
is that the SI controller may buffer up to 16 sectors internally.  When
a BSE or ECC error occurs the mba byte count register is correct, but not
relevant to where the *error* is.  The driver can be changed to calculate
the error location from the hpdc and hpda registers; this method works for
both SI controllers and DEC controllers.  The total changes (plus another
fix to increase throughput by disabling the lookahead calculation) are
only about a dozen lines.  Send email if you're interested.

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Jeff Gilliam	{ucbvax,ihnp4!nsc}!voder!jeff