[Simh] Simulating the PDP-15/76 Unichannel

[Johnny Billquist]

On 2015-03-19 14:13, Johnny Billquist wrote:
> On 2015-03-19 04:21, Timothe Litt wrote:
>> On 18-Mar-15 20:34, Rich Alderson wrote:
>>> [1] Developed mostly from RSX-11M, with a few nods to RSX-11D, at
>>>      least as far as the doc writers were concerned.
>> -11M, but -11D device drivers and a heavy dependence on event flags.
>> No memory mapping; it was a stripped-down environment.
>> 1 RP04/6 disk dual ported; the 11 driver had to deal with 18-bit (576
>> byte)
>> formatted sectors.
>> The queued protocol provided access to unibus peripherals, including
>> async lines, card reader, LPT and (my secret contribution, a
>> battery-backed-up
>> TOY).  This wasn't pure pass-thru; the 11 did a lot of the low-level
>> control and
>> presented abstracted devices.
>
> This is getting rather far off-topic, but anyway...
> Do you have any source for the claim about -11M with -11D device
> drivers? As far as I know, one of the major differences between -11M and
> -11D is just the device drivers, as the whole I/O subsystem was
> redesigned in -11M, for a smaller memory footprint and better efficiency.
> -11D could not run without an MMU, while -11M can. Thus it sounds
> strange that you'd have -11M with -11D device drivers. I would suspect
> that would be impossible, and in addition the -11D device drivers would
> require more resources than their -11M counterparts, which would be
> rather opposite of what was required of the 11/40 FE, which is rather
> limited on resources.
>
> My recollection of RSX-20F is that it very much feels like an unmapped
> -11M system. Some changes because of the special requirements, but
> nothing major.

Just re-read the RSX-20F manual (I had almost forgotten I had read it 
before).
In that manual, it is described in pretty good detail that they 
essentially just have an unmapped RSX-11M system. They added a device 
driver for the DTE-20, and a service task connected to that, and then 
just customized the whole thing.

The manual also mentions once or twice that RSX-20F also inherited 
something from RSX-11D, but there is nothing in the manual explaining 
what actually was inherited from -11D, so I'm not sure if I should take 
that verbatim, or just a relationship note, since -11M itself was 
designed based upon -11D.

	Johnny