Qbus slot ordering?

From: Chuck McManis <cmcmanis_at_mcmanis.com>
Date: Tue Dec 14 21:25:31 1999

At 03:24 PM 12/14/99 -0500, CLASSICCMP (Tim Shoppa) wrote:
> >Does anyone know if the CONFIGURE command in the VAX prom suggests slot
> >ordering in its output?
>
>No, it doesn't. The order of CSR's doesn't have any bearing with what
>cards go where in the backplane.

Oh well.

>The order of cards in the backplane will depend on interrupt and DMA
>priority. Generally, peripherals that *will* lose data if they can't get
>serviced in time get put closest to the CPU. Examples here are serial
>lines, etc. Next come peripherals that will have to do a retry if they
>don't get serviced in time, but they will be able to do a retry. Tape
>drives, for example, might come here. Finally come devices where there's
>no real penalty for a retry, and maybe the peripheral doesn't care at all
>if the CPU takes its own sweet time in dealing with it. Something like
>a real-time clock would come in this category.

Sigh, I read Alan's paper and it explained why things are the way they are
but it didn't help me figure out what the ordering should be since I don't
have enough technical specs on some of the cards to know what their
"latency tolerance" is.

FWIW, the DZV11 was apparently already set up to be the "first" one (I
stuck it in and did a show QBUS and there it was). That saved me from
having to figure out the switch settings. And so far it seems to not be
interfering with the operation of the system.

--Chuck
Received on Tue Dec 14 1999 - 21:25:31 GMT