On 04/01/2014 18:11, Robert Jarratt wrote:
Indeed, I can see that, but the MicroVAX 2000 firmware
manages to work it
out somehow, I just don't know how. The difference between the RD53 and RD54
seems to be entirely in the number of heads, so my guess is it tries to
detect the number of heads somehow. Of course it may do something completely
different, I don't know.
DEC were infamous for using "sniffer boots" during which the controller
would use a number of tricks to identify drives by their idiosyncrasies.
It does mean that apparently similar drives don't always work,
depending on the controller firmware revision, most notably with RQDX1/2.
Anyway, working out the number of heads is trivial. Every sector on any
vaguely conventionally formatted MFM drive has a header with an ID mark
which includes the track, sector and head numbers. So you just select
each possible head in turn, from 0 up to 7 (most drives) or 15 for
controllers that have a 4-bit head select, read a sector, and see if the
returned head number is correct. The first time it's not, you've just
exceeded the head count.
--
Pete
Peter Turnbull
Network Manager
University of York