John Hall wrote:
John Hall wrote:
> I think you'll find that the JCB is only updated when a task > switch occurs... > > When a TRAP#n is executed, the PC and SP are saved on the > supervisor stack, hence WL's earlier comment...
Oops! PC and SR, of course :-)
In supervisor mode, the job's SP is in the USP...
> > Now I can forsee there might be a problem if the calling job is > > in SV mode when it makes the Open call, as it would first have > > to exit SV mode before it could set up jobs, open channels and > > things, but it must sooner or later exit that mode, and the > > execution will procede as described. > > This is wrong, for the above reason.
Correction. This would work, so long as the job's PC could be found on the supervisor stack by the driver code...
...which, of course, it couldn't if the job had entered supervisor mode via TRAP#0 :-(
(Time to stop talking to myself and have a beer, I think!)
Hmm - this strategy would have benefits - however, it seems no-one is sure if it will work. Guess the only way to tell is to write a short test routine once the initial PFF driver is put together by Wolfgang - look forward to seeing what happens!!
-- Rich Mellor RWAP Services 26 Oak Road, Shelfield, Walsall, West Midlands WS4 1RQ
http://www.rwapservices.co.uk/
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