EDSI Problem

From: Jerome Fine <jhfine_at_idirect.com>
Date: Sat Jul 21 20:05:46 2001

>Ethan Dicks wrote:

> > Hi Jerome, have you tried moving your disk controllers closer to the
> > CPU? moving them up the bus grant chain will help. Also you can tell the
> > RQD11-EC to limit its DMA burst size which allows other boards to get in a
> > bus cycle when they need to. I had a problem where adding a SCSI controller
> > to a VAX killed disk performance on some ESDI drives but it was entirely
> > due to the SCSI controller doing large DMAs that interfered with the time
> > available for the ESDI drives to read or write buffers.
> Was that a controller for a TLZ04? We had problems with customers who tried
> to put a COMBOARD and a TLZ04 in the same VAX 4000 - it would lock up the
> microcode because of grant response issues. The TLZ04 card would grab the
> bus and our card would give up, but the CPU would try to give us a grant
> eventually, anyway. It wedged the computer so hard they had to power it
> off to unjam the bus. Apparently, the combination of a 1985 Qbus design
> that had never had to deal with a real timeout and a 1991 Qbus implementation
> didn't mix.

Jerome Fine replies:

I appreciate your reply and say thank for your input. However, although I do
have a uVAX II around somewhere, I have not turned it on for at least 3
years and don't plan to do so for another 3 years. The only Qbus hardware
(I stay away from Unibus hardware since I am too old to be playing with
such lethal weights) that I use is for the PDP-11 and the only operating system
I use is RT-11.

So your references to VAX hardware are not in my experience - although
the ESDI drives were probably a good fit for a VAX.

Sincerely yours,

Jerome Fine
Received on Sat Jul 21 2001 - 20:05:46 BST