Subject: Re: NetBSD/vax QBUS IDE?!
To: None <>
From: Charles H. Dickman <>
List: port-vax
Date: 11/22/2002 18:08:12
der Mouse wrote:

>>The proper way is to design a Q-bus IDE controller which speaks
>For what value of "proper"?  I feel confident I could (upon digging up
>Qbus and IDE documents) design a dumb IDE interface, like the one chd
>built.  I do not feel competent to design anything that speaks MSCP
>without some onboard CPU, which would, I would estimate, at least
>double the chip cost and greatly increase the hair involved.  Even
>then, I'd need MSCP documentation, and I have no idea where to find
>that.  (I don't know where to find Qbus and IDE specs, either, but them
>I've seen and thus I'm confident they exist.  MSCP docs could be made
>of unobtanium for all I know, and given DEC's aversion to publicly
>documenting its hardware protocols very well may be.)
I agree. I would rather have an interface in hand than a discussion of 
what would
be better that came to nothing. Talk about IDE/QBus adapters has been 
for at least 3 years. It usually progresses like this:

"Gee, an IDE drive on my VAX/PDP-11 would be cool because my RD53
just siezed."

"An IDE/QBus adapter would be trivial. I could do one next weekend, if I
had the time."

"But then there would be no driver compatibility. If it was MSCP then it
would work for everybody, on all platforms, and all OS's."


Somewhere in the middle, disparaging remarks are made about how bad
IDE is as a disk I/O standard.

I am not trying to be flippant, but each time this is discussed, the 
of the ideal is used to stamp out the practical, and then nothing happens.

The interface that I designed was purely for my own education. It has some
definite limitations. For use with my PDP-11, these limitations were 

In the last year, though, the possibility of an MSCP based disk controller
has been vastly increased by the existance of an RQDXn simulation in the
computer simulator written by Mr. Supnik. The fact that it is able to
fool the PDP-11 OS's, NetBSD, and VMS indicates that it is a reliable
prototype for implemenation. But, as has been suggested, this would
require a much more complex interface, including a processor.

Even more critical issues exist beyond the character of the controller.
QBus interface chips for the most part are obsolete. National still makes
some devices, but these are very expensive. There are always discrete
transistors, I guess......

If anyone wants more information or assistance with my feeble design,
email and I will help any way I can.