[Simh] Problem with reading tape with PDP-11 SIMH

[Alan Frisbie]

Before I dig too deeply into this problem, I thought I would ask
if anyone else has seen it, or has some insight.

I am running a relatively recent (mid-April) version of the
PDP-11 simulator on my Alphastation XP1000 with VMS v8.4.
The simulated PDP-11 is a copy of the physical 11/73 system
I had running RSX-11M v3.0 back in 1986.

So far, all simple things work just fine.

For instance, I can ATTACH a .TAP tape container file to SIMH
TS0, and read it (as RSX device MS0:) OK using FLX.   I can
also use DMP and other utilities to read the "tape".

The problem comes when I try to run TPC on the RSX system to
create a container file.   Since I was the TPC maintainer back
then, I am confident that it works correctly (at least for this
purpose).   What appears to happen is that the first 16 or so
reads of the tape complete OK, and the data gets written to
the new container file on the disk.   However, nothing happens
after that.

If I abort TPC and dump the next record on the "tape", it appears
to be about 16 records in from the start.   (I'll verify the
exact numbers next time).

>From this, it looks like SIMH may not be handling the read
requests after the first burst, or may not be properly giving
completion interrupts to the PDP-11.   Remember, TPC was written
to move a tape drive as fast as possible, so it will stress any
emulator.

I hate to blame SIMH so quickly, particularly with so few solid
facts, but this system (at least on physical hardware) worked
perfectly.

Does anyone have any ideas or suggestions before I start a deep
dive into the code?

Thanks,
Alan Frisbie