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<== Date ==> <== Thread ==>

Subject: Re: [Summary] CAMAC Serial Driver
From: watson@cebaf.gov
To: yamamoto@kekvax.kek.jp (Noboru Yamamoto)
Cc: tech-talk@aps.anl.gov
Date: Thu, 11 Jul 96 09:08:48 -0400
On the subject of CAMAC serial drivers, I note the following:

1) the original CEBAF/TJNAF version supports multiple IOC's sharing a 
   single serial highway, and no LAM support.  Single threaded operation 
   is guaranteed by disabling pre-emption during hardware access, and
   by using the hardware mutex for multi-IOC operation.  On hard errors 
   on the serial highway a short delay (~100 usec) is incurred.  
   Statistics are kept on the total number of operations, noX, and noQ.

2) the LANL version supports only a single IOC, but multiple serial
   highways, and with LAM support.  Single threaded operation is
   guaranteed by the use of semaphores.  On hard errors on the serial
   highway, a full 1 second delay is seen by the scan task processing
   the record if the expected interrupt is not delivered! We saw this
   problem this week -- the IOC appears to run 10,000 times slower than
   normal :)  Different statistics are kept, with some errors being
   tracked on a slot by slot basis, and other statistics kept by the 
   original version no longer tracked. A few useful convenience routines
   are included.

CEBAF/TJNAF is working on merging these two versions.  The choice between
semaphores and pre-emption disable will be made on the basis of performance,
although I suppose it could be a compile time switch for those who dislike
disabling pre-emption.


Chip


References:
[Summary] CAMAC Serial Driver Noboru Yamamoto

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