[Simh] Questions regarding future simulator development

[Johnny Billquist]

On 2013-04-11 22:14, Mark Pizzolato - Info Comm wrote:
> On Thursday, April 11, 2013 at 7:00 AM, Bob Supnik wrote:
>> 1. Four Massbus channels on the PDP-11 (or VAX). This is straightforward.
>> The RH simulator already supports two, and the extensions from two to four
>> use the existing mechanisms:
>>
>> - add the register blocks definitions to the header file
>> - define additional RHC, RHD devices with matching unit and register
>> definitions
>> - look for places where "2" is hardwired as the maximum number
>> - modify the autoconfiguration table for the additional device addresses
>
> This is most of it, but additional devices and units must also be defined in the pdp11_rp and pdp11_tu which then need to be connected to the new RHC and RHD devices created above.  Maybe a way to dynamically assign particular rp or tu devices to  a particular Massbus is also be necessary (someone might want 3 disk controllers and 1 tape, while others might want 3 tape and 1 disk controller, etc.).  If mixed configurations are possible something needs to validate that there are no Massbus conflicts.

Isn't there already? I mean you should not be able to attach two 
different disk drives with the same unit number. And that is the only 
kind of conflict you can have.

 From an RSX point of view, even having an RM and an RP disk on the same 
Massbus is considered a mixed Massbus. Like I said before. RM and RP are 
not the same from the host point of view, and should most likely not be 
considered the same from simh point of view either. But that is another 
issue.

Conflicts, as such, can only be about the unit number.

>> 2. While real documentation for the RS03 and RS04 is lacking, they are
>> described in adequate detail in the early PDP-11 IO handbooks, which are on
>> BitSavers. This would probably suffice to run the operating systems, but not
>> diagnostics. There is also some information on issues in the RS03 and RS04 in
>> the Massbus standard.
>
> Good to know.
>
> This, along with the driver sources which Johnny Billquist mentioned are probably sufficient for someone to implement things.

Yeah. I don't expect that it would be very difficult if someone wanted 
to add more Massbus devices.

	Johnny