[Simh] Custom ROMs on PDP-11 sim

[Johnny Billquist]

Top-posting to make it simple, while still keeping the original text.

While it is true that device access might be done using relative 
addressing, that would in general be a bad software design. Things like 
device CSRs should never be accessed as relative addresses, but should 
be absolute. Any sane programmer should know that. And it is not any 
extra effort in doing this on a PDP-11, so the programmer have no real 
excuse for not doing it right. (But I know that people sometimes still 
do things wrong anyway.)

However, that said, actually writing programs fully PIC on a PDP-11 
takes a little more effort, and many times, people didn't do that, so 
there is a risk that the program really needs to run located on the 
addresses given by the card.

But, as have been said several times now, this is all moot. Without the 
ROM contents, nothing to really do here.

   Johnny

On 2017-12-16 12:14, Timothe Litt wrote:
> 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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-- 
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