Qbus slot ordering?

From: CLASSICCMP_at_trailing-edge.com <(CLASSICCMP_at_trailing-edge.com)>
Date: Tue Dec 14 14:24:45 1999

>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.

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.

>I ask because I'm trying to configure my uVAX with an additional 4 serial
>lines using either a DHV11 (get an extra 4) or a DZV11. In the former case
>no matter how I type in the devices, it organizes the DHV11 as the last
>thing on the bus. When I type use the DZV11 it puts it at the head of the
>list (even ahead of the DELQA which seems unusual)

What you're seeing there are the CSR autoconfigure rules in action.
They're largely historical; the DZV11 is based on the DZ11, which is
an "old-time" async multiplexer, and comes early in the autoconfigure
rules. The DHV11 came many years later, and comes much later in the
autoconfigure rules.

If you're interested in knowing where the autoconfigure rules come from and
how they're applied, take a look at Alan Frisbie's DECUS presentation at


 Tim Shoppa                        Email: shoppa_at_trailing-edge.com
 Trailing Edge Technology          WWW:   http://www.trailing-edge.com/
 7328 Bradley Blvd		   Voice: 301-767-5917
 Bethesda, MD, USA 20817           Fax:   301-767-5927
Received on Tue Dec 14 1999 - 14:24:45 GMT

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