[Simh] Questions regarding future simulator development

[Christian Gauger-Cosgrove]

Hello Mark,

On 10 April 2013 13:37, Mark Pizzolato - Info Comm <Mark at infocomm.com> wrote:
> Anything is possible.  Someone could extend a particular simulator instance to implement a something (a GUI perhaps) which provided a way for a user to express the desire to perform one of these actions and to gather the needed details relating to the desired action.
>
> Hooks exist in the codebase to allow a particular simulator to provide what can be reasonably described as arbitrary extensions the basic simh framework.  These extensions can include both simulator specific commands and/or arbitrarily anything else.
>
That is understandable, though my question would have been better
phrased as "would the rewrite of the code to separate the simulator
command processor from the simulator CPU into different threads be
something that requires a massive rewrite of the codebase?"


> Once again, anything is possible, but this would be a significant amount of work.   If there was some formal documentation available which described the RS03 and RS04 disks, then adding them to the pdp11_rq.c code would probably not be too hard.  Looking in the 'usual places' on bitsavers.org doesn't provide any information on these disk devices though.
>
Well it would be to the pdp11_rp.c code, but either way, they're just
another form of MASSBUS disk, and in my quick browse through the
pdp11_rp.c code, it looks likes like the various drives under its
purview are only defined as their geometries. So to add the RS03 and
RS04, all that would be needed to be added -- in my quick glance at
the code, would only require entering the proper geometry for the
devices.

> Meanwhile, there already exists support for many disks within the current simh codebase.  There is existing support for 4 RQDX controllers each of which can support 4 drives.  The RL controller can support up to 4 drives.  The RP can support up to 8 drives.  The HK (RK611) can support up to 8 drives.
>
Speaking of the RK611, I noticed a problem, whereby an RK07 errors out
in RSTS/E (10.1-L) with "device not ready" or something similar, while
it works just fine with an RK06... weird.

There is only one set of drives that isn't implemented in SIMH at
present, is the pre-MASSBUS RP drives (on the actual RP11 controller,
so RP01, RP02 and RP03). But I don't think much if any still extant
software even supports the RP0[1:3].


> Simulated systems can easily be configured which could have never exist in the real hardware space due to issues like 1) cost, 2) concurrency of technology, 3) power/bus loading constraints, etc.  Yes, you can't currently configure a system which could have arbitrarily been designed with real hardware, but you can also configure many system configurations which exceed many of the assumptions which existed when working with real hardware.
>
Of course it is possible to "misconfigure" a system, But I know in my
own case, I try to keep any system configurations limited to what was
actually possible (with the occasional waiver, e.g. having the RP
drive series plus its associated RH controller on a QBUS system with
the justification of "somewhere there is a third party board that
let's you put a CDC 9766 on a QBUS box".

Plus the simulated system has allowed the debugging of software with
proper configuration issues. (The example of choice being the "XVM/DOS
doesn't play nice with an RF15 with 8 platters, only a maximum of 7.")


> Once again, anything is possible.  There are no magic bullets here.  Someone with sufficient motivation, skill and detailed information would have to make the effort to do these types of things.
>
Once you again you are very correct, but I am not the person to
implement anything; while I am enthused about getting some of which I
mentioned working, I couldn't program it worth anything.


Cheers,
Christian