[Simh] DZ11 vs DZV/DZQ11

[Johnny Billquist]

On 2018-04-09 21:12, Robert Armstrong wrote:
> *>….*single PDP11 simulator can simulate different PDP11 models …
> 
>    Yes, and the UNIBUS and QBUS peripherals don’t always map exactly in 
> functionality.  Actually I’m surprised this situation hasn’t come up 
> before with other devices.

Depends on how you look at it. I've certainly had issues in the past 
because I tried to do things like in the real hardware, which simh just 
couldn't deal with. But you often adopt to what simh actually can do...

>>Feel free not to use the extra ports that are provided free of charge. J
> 
>    You’re right – for the most part it doesn’t matter.   But, … if 
> you’re using the DZV/DZQ simulation with a TELNET port (which I imagine 
> is what most people do) then I don’t think you can stop simh from 
> accepting a connection for lines 4..7 if the first four lines are 
> already busy.  And if you want to simulate a QBUS machine with 8 lines 
> and two DVZ/DZQ cards, then what the OS actually sees is all eight 
> connections coming in on the first card and none on the second card.  I 
> haven’t tried it yet, but I don’t know what the various -11 OSes will do 
> when they get activity on lines that can’t physically exist.  Probably 
> they use the same driver for both the DZ and DZV so they won’t care, but 
> I don’t know that.

Of course they care! When a character is received on a DZ line, the 
driver have to map that into a device. Which, in this case, will be a 
device that does not exist.
It will not be mapping them to the devices configured for the second 
controller.
Or at least RSX certainly won't.

>>  What should happen when an odd number of DZV11’s are configured and 
> the CPU type is changed…
> 
> Well, ideally there should be an error or warning message, but I imagine 
> that’s difficult to implement.
> 
>    For me, I’d be happy if simh was changed to accept “SET LINES=…” in 
> multiples of 4 rather than multiples of 8.  It’s true that this would 
> possibly allow you to create invalid DZ configurations, but in my mind 
> the possibility of deliberately defining an invalid configuration is 
> less annoying than the impossibility of defining a valid configuration.

It's hardly invalid to have a controller where not all lines are 
connected to anything, and are not actually configured in the OS to map 
to any device. You can configure RSX to have two DZ controllers, and 
only two terminal lines, one on each controller. Any characters on any 
other lines than the ones you have configured will be dropped by the 
driver. And there can actually be good reasons for such configurations. 
Each device takes up memory. So don't configure in devices you'll never 
use, including extra terminal lines. But RSX can also talk DECnet over 
serial lines. But DECnet requires its own controller, and cannot share 
it with the normal terminal driver. So, if you want one serial line, and 
one DECnet asynch DDCMP connection, you will need to configure two DZ 
controllers, but you might very well only be interested in one line on 
each controller.

   Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol