[Simh] attaching a tape virtual file without stopping simulation

[Hittner, David T.]

Another possibility is to use multiple tape drives, with the extra tapes premounted, and switch to next tape drive.
Wasn't BACKUP modified at some point to take a list of tape drives that it would use sequentially?
 
Yet another possibility might be to modify the TELNET subsystem to give you a tape change prompt when issued a <break> or some other special command.
 
Dave


________________________________

	From: simh-bounces at trailing-edge.com [mailto:simh-bounces at trailing-edge.com] On Behalf Of Boucher, François
	Sent: Tuesday, January 22, 2008 2:09 PM
	To: simh at trailing-edge.com
	Subject: Re: [Simh] attaching a tape virtual file without stopping simulation
	
	
	>> How can I attach a tape virtual file to the TQ0 simulated device in simh 
	>> without stopping simulation with CTRL-E ?
	 
	>You can't, but you do have 20 seconds to do it before the system(s) will 
	>crash with a CLUEXIT bugcheck. When I was doing some experiments, I was 
	>able to unload and load tapes in the SIMH console within the 20 second 
	>period.
	 
	>You can also change the SYSGEN parameter RECNXINTERVAL to have a larger 
	>timeout.
	 
	>--Marc

	 

	 

	Marc, you are great!

	 

	I knew i had a bit of time to do the job before the crash happens. This 20s time frame is about the

	same also about disks that are being attached/detached in SIMH while stopping simh.  The major drawback is that it implies

	a human has to mount the tape file, and that human has a limited amount of time before the crash will happen.

	In the place where I work, where we still have computer operators,  I would prefer an automated attach

	process... 

	 

	I will try the solution of modifying RECNXINTERVAL anyway to increase it's time.  Thanks for your suggestion.

	 

	I am also inclined of checking if I can get simh by changing source code to automatically always

	attach itself to a given file name, but when it detaches itself, to make it rename the virtual tape file,

	so the tape file does not get overwritten.

	 

	In pseudo-code, this would be my idea:

	Let's say tape.tap is the virtual tape file. And let's create a simh variable say sim_auto_attach wich could

	be TRUE (tape will always have a virtual file in it) or FALSE (actual behaviour).

	 

	In sim_detach(),

	Run function as usual, detach tape metafile from tape device.

	If simh parameter sim_auto_attach == TRUE, then  

	Rename tape.tap to tape#.tap where # is a unique number (date and time?)

	call  sim_attach() with the tape.tap file as the target file argument.

	Return()

	 

	 

	It could also be possible to create a parameter with the auto-attach file name, instead of the tape.tap constant.

	 

	A little auto-critic on my above solution is that this is good for WRITING backup savesets to the tape.

	It is not usable for restoring.  Another virtual tape drive has to stay manually controllable to attach/detach

	the virtual tape file. 

	 

	Brian Knittel also makes a very interesting solution, to have at long time intervals (ie .1sec) the simh check

	for the existence of a command file that contains commands to attach/detach files.  This command file could be written

	With the same syntax as vax.ini for example, and it contents be executed by the do_cmd() function from simh.

	 

	This would be a great solution to my RESTORATION process, when one would need to have a tape attached

	for reading purposes.  Brian's solution is more universally applicable, but might need more human interventions,

	than the auto_attach modification.

	 

	Thanks again, Marc and Brian, I value your inputs very much!

	 

	Best regards,

	 

	Francois Boucher ing.

	 

	 

	 

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