Sun VMEbus adapters

[John A. Shriver]

Yes, at least the original Sun VME 3->2 adapter caused boards using it to
fail to meet the VMEbus specifications.  The problem is that the wires on
the adapter's PC board use up all of the "stub" budget for cards on the
VMEbus.  All transceivers have to be within some very small distance
(about 2 inches) of the pins on the board.  I think Sun redesigned the
adapter so that the etch was shorter, but it still could cause problems
with reflections.  (It might also generate some crosstalk.)   The timing
on the VMEbus is very tight, so one has to watch the transmission line
stuff carefully.

Of course, the adapter works fine with Sun's boards, but the SCSI
controllers are not high-speed 32-bit DMA devices.

There are third-party adapters which do not have any connectors, and are
just a peice of plastic that attaches to the edges of the board, to bring
it up to 9u size.