Oops, tbuf errors again

[Bruce Nemnich]

The L0003 should be the board to swap, since that's where the tbuf and
cache are.  We had an L0003 swapping session which lasted a week or so
in September, I believe.  DEC accidentally shipped us an extra L0003
with some other hardware (!).  I tried it out, but it was considerably
worse than the one I had been running.  I had DEC bring in a new one,
but it would halt the machine every 8 hours or so.  Finally, two boards
later, I got one which performed much better than any of them.  I kept
that until I got rev 7.  So, there is a wide range of failure rates.

One of the guys installing it said the problem was caused by crosstalk
between two layers of the L0003 board.  One ECO (don't know which) put
jumpers on the board to help but not cure the problem.  The PCS
microcode 98 claims to fix it by retrying after the first failure per
macroinstruction, but trapping on subsequent errors.

How can you have "rev 7 hardware" without the PCS?  That's part of the
FCO.  There are two versions, one for those with the user WCS and one
for those without.
-- 
--Bruce Nemnich, Thinking Machines Corporation, Cambridge, MA
  ihnp4!godot!bruce, bjn at mit-mc.arpa ... soon to be bruce at godot.arpa