rg@msel.unh.edu (Roger Gonzalez) (04/08/91)
I recently wrote a SCSI device driver that controls a WORM optical drive.
It actually isn't a Unix device driver, since the WORM schema wouldn't
allow a Unixish file system on it without having all dynamic tables on
a separate hard drive or something. But I digress. Although this isn't
a strictly Unix question, I have a feeling that people who have written
Unix drivers should be able to help me.
A frequent occurence in the driver is that I want to set some register bit
high, but I'm not allowed to do it until some other bits go to a certain
state. My first cut driver used plain 'ol polling with a timeout. This
worked ok, but beat the piss out of the VME bus. I then changed it so
that my polling went more like this:
while ((reg != val) && (counter < timeout))
usleep(N); /* yeah, yeah. non-portable SunOSism. BFHD. */
Now my driver is slightly kinder to the bus, but runs like molasses.
Is there a generally socially acceptable way to handle this?
(Note - this whole thing is further complicated by the fact that not only
do I go out over the VME bus, but from there I go out over a Bit3 VME adaptor
boardset to a remote VME bus.)
Thanks!
-Roger
--
"The question of whether a computer can think is no more interesting
than the question of whether a submarine can swim" - Edsgar W. Dijkstra
rg@[msel|unhd].unh.edu | UNH Marine Systems Engineering Laboratory
r_gonzalez@unhh.bitnet | Durham, NH 03824-3525