SUN Multibus/VMS adaptor help needed

[Steve Gilgut]

We have been trying to get one of our Multibus boards to work on a Sun 3
using a VME-to-Multibus adapter board. The board has two parallel channels
and two serial channels (all controlled by an Intel 8237A DMA controller,
serial channels programmed through a Zilog Z80-SIO chip). Parallel and serial
channels are driven through separate device drivers. The board has been working
in Sun 2 systems for about 2 years now with no problems.

When we use Sun's VME-to-Multibus adapter, both parallel channels work properly,
but the serial channels cause 'Spurious level 4 interrupt' messages. The
adapter dip switches are set to generate a vector of 1C (hex) and the
trap vector for level 4 spurious interrupts is at 18 (hex). Notice that only
one bit is different in the two vectors. The problem seems to be timing, since
adding printf's to the serial driver makes the problem go away (obviously by
slowing things down) and the parallel channels interrupt at the same address
with no problem (the frequency of interrupts there is much less).

So the question is, does anyone out there know of this problem with the
adapter board, and possibly a way around it? Please send responses to
decvax!cg-d!fathi. Thank you.

					Ben Fathi