Experimental Physics and
Industrial Control System

Mark Rivers <[email protected]> · Sat, 5 Aug 2000 18:47:05 -0500

Folks,

I have a question about the EPICS sequencer program.  There does not seem to
be a way to invoke ca_put_array_callback from within an SNL program, only
ca_array_put.  This seems to be a serious limitation.  For example, I have
an SNL program in which I want to write 4 strings to a stringout record.
...
    strcpy(stringOut, 'string 1');
    pvPut(stringOut);
    strcpy(stringOut, 'string 2');
    pvPut(stringOut);
    strcpy(stringOut, 'string 3');
    pvPut(stringOut);
    strcpy(stringOut, 'string 4');
    pvPut(stringOut);

What happens is that only "string 1" and "string 4" get written to the
device, because the record is busy processing when "string 2" and "string 3"
are sent, so they are never sent, channel access throws them away and only
sends the last one, "string 4".  I could call taskDelay() after each
pvPut(), but this is ugly.  It seems to me that the SNL needs a
pvPutCallback, so that it is possible to wait until the record is done
processing one string before sending the next.

Do others agree that this would be useful, or am I missing some other way to
accomplish what I need?  Is there a version of the sequencer which already
has this feature added?  A quick look at the code leads me to think that it
would not be very difficult to add, since synchronous pvGet is already
supported via a callback and semaphore.

Cheers,
Mark Rivers

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System