[Simh] Adding a third massbus to the VAX780 emulator

[Peter Allan]

Thanks to all for your comments.

Kevin, yes I could define logical names that would let me refer to the
drives using the names DRA0 and DRA1, but they would still show up as DRA2
and DRA3 on the output of "sho dev d" for example. I would like to do
better if I can.

Johnny, I agree in principle, but I really don't want to get into rewriting
too much of SIMH.

Mark, that sounds like a very useful suggestion and I will look into how
the RQ controllers are implemented. Hopefully it will indeed let me add any
drive to any massbus, which is as it should be. If I succeed, it should be
generally useful. My original suggestion was clearly a "dirty hack" and
even if it worked, would not be suitable for airing in public.

Cheers

Peter Allan

On 21 November 2012 22:09, Mark Pizzolato - Info Comm <Mark at infocomm.com>wrote:

> Hi Peter,****
>
> ** **
>
> I have no specific knowledge of how multiple mass busses may be ‘wired’
> into simh.  However, once you figure that detail out. I suggest that you
> consider the idea of extending the existing pdp11_rp.c to support multiple
> ‘device’ instances where each device is attached to a desired massbus and
> has its own set of units.  You may want to look at how pdp11_rq.c supports
> multiple RQ instances as an example.  Meanwhile, if you’d ever like to have
> your changes make it back into the general simh code base, then please
> start from the latest pdp11_rp.c which can be found at:
> https://github.com/simh/simh/blob/Extra-VAXen/PDP11/pdp11_rp.c and a zip
> of the current Extra-VAXen branch at:
> https://github.com/simh/simh/archive/Extra-VAXen.zip****
>
> I am in the middle of tracking down a bug in this code right now (
> https://github.com/simh/simh/issues/14), so feel free to start looking at
> things now, but be prepared to take an update to pdp11_rp.c when I resolve
> the issue.****
>
> ** **
>
> Good Luck,****
>
> ** **
>
> **-          **Mark Pizzolato****
>
> ** **
>
> *From:* simh-bounces at trailing-edge.com [mailto:
> simh-bounces at trailing-edge.com] *On Behalf Of *Peter Allan
> *Sent:* Wednesday, November 21, 2012 12:27 PM
> *To:* simh at trailing-edge.com
> *Subject:* [Simh] Adding a third massbus to the VAX780 emulator****
>
> ** **
>
> Many, many years ago, I used to be the system manager of a VAX-11/780
> system that was part of the Starlink astronomical data processing network
> in the UK. One of my pet projects is to have an emet defulation of this
> as close to the original as I can get it. The system had two RP06 disk
> drives and two System Industries drives that emulated RM05 drives. Since
> the System Industries drives interfaced to the 780 through their own
> massbus adapter, the RP06 drives appeared as devices DBA0 and DBA1, and the
> emulated RM05 drives appeared as DRA0 and DRA1.****
>
>  ****
>
> I can create a similar system using simh, but with all of the drives on a
> single massbus, the drives appear as devices DBA0, DBA1, DRA2 and DRA3.
> This apparently trivial difference annoys me so I am looking for a way of
> having both the RP06 and RM05 drives appear as units 0 and 1.****
>
>  ****
>
> I presume that this will require modifying simh to add a third massbus
> adapter. (Please do tell me if there is an easier way.)****
>
>  ****
>
> Having looked at the simh code, I am reasonably confident of being able to
> add a third massbus. However, how can I attach RP drives to one massbus and
> RM drives to another? Both drives are handled by the same function, i.e.
> pdp11_rp.c. My thoughts at the moment are that I should copy pdp11_rp.c to
> a new file pdp11_rm.c and remove the code that handles the RM disk from
> pdp11_rp.c and vice versa for the RP code in pdp11_rm.c****
>
>  ****
>
> I can see that there is more work to do in terms of splitting the handing
> of interrupts and the like, but before diving in, does my basic strategy
> seem correct? It would be more like real life (I think) to be able to add
> RM and RP drives to both massbuses that handle disks, but I don't see how
> to do that without a lot more work.****
>
>  ****
>
> And before anyone says it, I know I am mad to be trying to do this. The
> effort is clearly disproportionate to the benefit, but it is a hobby after
> all.****
>
>  ****
>
> All comments gratefully received.****
>
>  ****
>
> Peter Allan,  petermallan at gmail.com****
>
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