Multiple Bus Master Problem

[Paul Macdougal]

I tried to put a DMA device into a Sun 4/110 chassis (3 VME slots) and
failed to get it running.  I later found out that this backplane and
similar 3 slot ones made by SUN are not set up to allow multiple bus
masters!  Has anyone else seen this problem?  Can it be true that only
slave VME boards can go into these backplanes?  Also, what about the
SparcStation 330? with three VME slots?

---> Paul MacDougal
macdouga%stdc01 at rti.rti.org

[[Received later -bdg]]

Earlier I posted a mesasge about a problem with having multiple masters
in a 3 slot backplane.  Here is a clarification of the situation.

    The Sun 4/110 CPU board was designed without the proper bus
arbitration logic to support another VME master.  As far as I can tell,
this is the only board Sun has made which has this defect.  Therefore,
you cannot place any VME cards in a Sun 4/110 which require the ability
to grab the bus (e.g. DMA devices).  This situation is documented in the
SUN support literature, but most field service representatives don't
know about it.

---> Paul MacDougal 
rti!stdc01!macdouga 
macdouga%stdc01 at rti.rti.org