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

Subject: Re: I/O Interrupt Scanning for Soft Records
From: nda@aps.anl.gov (Ned Arnold)
To: tech-talk@aps.anl.gov
Cc: ajf@ast.cam.ac.uk
Date: Mon, 24 Jul 1995 09:55:19 -0500
> Could the soft records be modified to support I/O Interrupt scanning 
> when their input is a CA link, such that when the CA monitor is 
> triggered it causes record processing?  
> 
> Any hints on how we should go about doing this?
>
> Andy Foster
> Royal Greenwich Observatory


The WAIT record in R3.12.1 implements this feature. All input PV's (they are
not actually "links" because they can be changed without rebooting) have
monitors set on them. If the scan mechanism is set to I/O INTR, the record
processes every time a monitor is posted on an input PV. (The code tha does
this is in recWaitCa.c).

There are a few short comings to this implementation ... 

 1) The input PV has to be located in the same IOC. This is on our list to
    correct, maybe your requirement will increase the urgency. (Marty, where is
    it on your list ???)

 2) The implementation is pretty specific to the WAIT record. I would like
    to see this feature implemented in a generic way, such as a third flag 
    on input links to process the record on a monitor post. This is a much
    more aggressive change, and unlikely to come along very soon (CA Version 4?)

So, there are a few hints. If you only have a few of these (10-20), I think a
small SNL program is a great <temporary> solution. SNL programs are NOT 
a hassle at all, in fact they have some very significant advantages, such as
a proven Channel Access client implementation, changing the logic without
rebooting, and easy to read and maintain (easier than custom/unique record
support). 


	Ned



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