[Simh] Custom ROMs on PDP-11 sim

[Timothe Litt]

On 15-Dec-17 22:14, khandy21yo wrote:
> Can't you just load them into ram and run them from there?
> Rom is just non writable memory.
>
>
He could, except that these ROMs are probably in I/O space, so would need
to be part of a simulated device for any code to execute properly[1]. 
(And any
code in them probably touches the device registers, so you need the device
to get anywhere.)  As Mark pointed out, SimH doesn't currently support any
devices that way - it does functional emulation of I/O devices.  (It
wouldn't
be difficult to write such a device emulation if there were a reason to.)

However, to disassemble code/view data, they could be loaded into any RAM
address & poked at with the SimH console.

Some reformatting would be required, since ROMs of that era would
typically be
byte-wide, with 2 devices/word - e.g. one ROM contains the even bytes,
another
the odd ones. (There are other organizations.)

FWIW, ROMs in I/O devices tend to be one or more of:

  * Code for on-board processors (rare in early PDP-11s, but Ethernet
    and (t)MSCP boards had them)
  * Identifying data for the device (e.g. device type, model, serial,
    timing, geometry, etc)
  * Bootcode/self-test/primitive driver for the host to execute
  * Data for the host (e.g. Fonts or strings)

However, as Aaron says that the devices have been erased, it's all moot
at this point :-)

So that's probably more than you wanted to know...

[1] While the code would likely be PIC, things like references to the
device's registers would also be relative to where the code is loaded. 
Looping on a "done" bit relocated to RAM is likely to be frustrating...

>
> Sent from my Galaxy Tab® A
>
> -------- Original message --------
> From: Aaron Jackson <aaron at aaronsplace.co.uk>
> Date: 12/15/17 10:37 AM (GMT-07:00)
> To: Mark Pizzolato <Mark at infocomm.com>
> Cc: simh at trailing-edge.com
> Subject: Re: [Simh] Custom ROMs on PDP-11 sim
>
> Hi Mark,
>
> It probably does not matter anymore unfortunately. I have a PDP-11 from
> a Unimation PUMA robot, which has a 16x EPROM board in it but no power
> supply. I was hoping to try running what was on them inside a
> simulator. I started dumping them and realised that they have all been
> erased before it was sent to me.
>
> Of course I could have tried installing the card in my PDP-11/73 but I
> thought there might have been an easier way with the simulator.
>
> Never mind, thanks anyway.
>
> Aaron.
>
>
>
>
>
> Mark Pizzolato writes:
>
> > Hi Aaron,
> >
> > On Friday, December 15, 2017 at 7:18 AM, Aaron Jackson wrote:
> >> I am wondering if it is possible to use attach ROM dumps in the
> PDP-11 simh?
> >> I haven't found anything about it in the documentation. If not, I
> suppose it
> >> wouldn't be too hard to modify the bootrom header.
> >
> > The PDP11 simulator (which simulates MANY different PDP11 models)
> doesn't
> > actually use any ROMs and doesn't currently support simulation of
> any cards
> > which user supplied ROMS might have been installed in.
> >
> > What problem are you trying to solve???
> >
> > - Mark
>
>
> --
> Aaron Jackson
> PhD Student, Computer Vision Laboratory, Uni of Nottingham
> http://aaronsplace.co.uk
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