I think this is totally the wrong strategy. If anything, you should try
to model this as close to how the actual hardware worked, and not do
some special thing that happens to just match your very specific
configuration.
What you need is to split the massbus handling, as such, from the
specific disks. You should then be able to create massbusses for you
machine, and then you attach disks to the massbus. It is a hierarchy,
and the config should reflect that.
I think simh's current approach of presenting things in a very flat way
is a bit too simplistic. I got annoyed the other day when I wanted more
than one DZ11 on a configuration, and realized I could not configure the
controllers as such at all, but instead configured the total number of
serial lines, with an implicit overflow from one controller to the next.
In real life, you might have a machine with four serial lines, but all
attached to separate DZ11.
Just specifying the endpoints without the ability to specify the
configuration in the middle layers will cause issues like the ones you
have, because simh then makes assumptions for you. (Such as having just
one massbus, and all disks attached to that one.)
In fact, I wonder if this will actually totally break something like
RSX-11M, which do not allow mixed device massbuses. Ie. in 11M you
cannot have both RM and RP disks on the same massbus.
M+ allows this, but then, M+ is rather more advanced... :-)
Johnny
On 2012-11-21 21:27, Peter Allan wrote:
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 emulation 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, [email protected] <mailto:[email protected]>
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