[Simh] Error in DMC11/DMR11 Emulation in RSTS/E 10.1

[Mark Pizzolato]

On Sunday, January 3, 2016 at 5:25 PM, Paul Koning wrote:
> > On Jan 3, 2016, at 6:42 PM, Christian Gauger-Cosgrove
> <captainkirk359 at gmail.com> wrote:
> >
> > On 3 January 2016 at 16:42, Paul Koning <paulkoning at comcast.net> wrote:
> >> No, that's not what that means.
> >>
> >> It does say that micro diagnostics are required; when those are disabled,
> the device is rejected because of that failure.
> >>
> > Note that XM0 and XM1 provide the same "XMn: is missing ECO's, but
> > will still function" as XM4; and XM4 has the micro-diagnostics
> > DISABLED all three of those devices are TYPE=DMC and INIT accepted all
> > three. The rejected devices are XM2 and XM3 which were defined as
> > TYPE=DMR (one with and one without micro-diagnostics).
> 
> I found why.  In pdp11_dmc.c, if a master clear is done on a DMR that is not
> currently attached, a micro-diagnostic failure status is posted.
> 
> I'm not sure if that's a good idea.  In RSTS, this test happens at boot, and if at
> that time you're not attached, the device will be disabled because of that
> failure status.  Attaching later on then won't help.  It may be better for
> unattached to produce some more benign status (or, perhaps, simply to
> result in no communication so DDCMP startup will time out in the same way it
> would if the remote system were down).
> 
> So attach the device in SIMH before boot, and things will work.

This is a basic requirement of functionality.  Having the DMC/DMR device "ATTACHED" merely means that the desired peer endpoint is "described", not the fact that a connection exists yet.  This is like having the device connected to some sort of Modem/DSU.  The external wires on the DSU don't need to be plugged into anything, but the modem must be present for the network to have the "potential" to work at some time later.

This category of device isn't like a tape drive or a removable disk.  Dynamically attaching and detaching this device while a system is operating is not a normal activity.  Users should merely provide the appropriate ATTACH command immediately after enabling the device and describing the peer.

- Mark