[Info-vax] axpbox crashed when logged out.

[Stephen Hoffman]

On 2020-11-18 03:34:02 +0000, Timothy Stark said:

> I discovered a bug in axpbox when I attempted to log out.  Axpbox 
> crashed with messages:
> 
> 
> Exception in SYM thread: Not implemented: pci0.1(sym53c810).disk0.4(file):
> Unknown SCSI command 0x1b.
> 
> : /home/sword7/axpbox/src/src/Disk.cpp, line 1495.
> 
> Emulator Failure: Threading error: SYM thread has died:
> /home/sword7/axpbox/src/src/Sym53C810.cpp, line 1501
> 
> Stop threads: cpu0 srl0 sym ali kbd
> 
> Freeing memory in use by system...
> 
> pci0.1(sym53c810).disk0.0(file): Closing file.
> 
> 
> 
> I checked SCSI reference for command 0x1B and it performs 
> loading/unloading or starting/stopping unit.  I believe that logout 
> routines attempted to unload CD om DKA400 (53C810).
> 
> I was able reproduce errors at some chance when I attempted to log off.
> 
> 
> Does anyone have any experience with that?

Any experience with emulated hardware issues, and with actual hardware 
having issues?  Sure. This case is basically buggy hardware.

Experience with SCSI issues? Absolutely. Lots.

With this particular emulator and this issue? No.

Check with the emulator maintainer.  axpbox hasn't been getting all 
that much traffic around here as yet, and I don't know that the 
maintainer follows this usenet newsgroup or receives feedback from 
postings here.

Or have a look at the emulator itself. At the emulator source code. 
Solely from what you've posted and not having reviewed the source code, 
this looks like a fairly reasonable setup within the emulator code.

SCSI 0x1b is start-stop and load-unload. Prolly a stop request, here. 
An unload is possible and certainly easy to test, but OpenVMS doesn't 
unload devices at shutdown, nor at logout. Start-stop and load-unload 
are not really particularly relevant commands for an emulator, so it 
can likely be ignored save for updating some internal device state 
settings within the emulator. Pull down the emulator source code and 
have a look at the Disk.cpp and Sym53C810.cpp source code, and at 
whatever code parses the SCSI command packets and generates the SCSI 
command responses.

Based on what the OpenVMS shutdown does and on what logout does and 
what the emulator is reporting, I'd suspect this is a disk spindown 
request.

SCSI is a command-response protocol, so OpenVMS drivers and some 
user-written apps send SCSI commands at the SCSI controller or the SCSI 
device, and the device then parses and processes the command request 
and generates what the device considers an appropriate response. Part 
of the "fun" of  SCSI is the flexibility and variability of the 
possible responses and of the timing of same. SCSI's gotten easier to 
deal with in the last decade or two, but it's still possible to bump 
into incompatibilities and unimplemented commands and unexpected 
responses. SCSI weirdness was far more common in past years, and 
OpenVMS SCSI processing itself has gotten better. V6.2 and V7.1 saw 
substantial improvements, there.

In this case, the emulator doesn't recognize the SCSI command, and 
crashes. SCSI hardware and particularly SCSI firmware does that 
sometimes, too—crashes, lock-ups, hangs.

FWIW, USB is basically SCSI with random bus disconnects, and ATAPI is 
basically SCSI operating atop IDE.

I'd probably add command packet dump to that crash code; a way to dump 
the full SCSI command packet to the user. Longer-term, I'd usually just 
write the above crash info and the command buffer to a logfile 
somewhere or to a crash report that can be available to the maintainer, 
and generate some benign description to the user; an I/O feature not 
implemented by this version of the emulator, in this case. With where 
to look for more data and/or how to report this error and/or seeking 
permission to upload the related telemetry.

-- 
Pure Personal Opinion | HoffmanLabs LLC