Experimental Physics and
Industrial Control System

Kurt Biery <[email protected]> · Wed, 10 Jan 2007 08:22:49 -0600

Hi Jeff,

This note is a follow-up to my earlier posting on tech-talk regarding

the buffering of string and array record data. (Thanks for your reply!)

As I mentioned in my tech-talk message, we would like to use process

variables in soft IOCs to pass string messages between processes in a

DAQ system that we're designing. I should have been more careful in

that email, though, to mention that we're not suggesting that lots of

large messages get buffered for long periods of time. Rather, I was

asking how one might configure EPICS to gracefully handle (reasonably

short) bursts of messages in a system in which the average rate of

message production can easily be handled by the subscribers. For

example, the scenario that I presented in my tech-talk message which had

a waveform record of 32 bytes being quickly updated 100 times and then

left alone for a long time seemed like a scenario in which we might

reasonably expect the 100 messages to be reliably delivered. From the

tech-talk responses that I received, though, it sounds like the graceful

handling of bursts would be an enhancement rather than something that we

can configure.

I described all of this to the NOvA DAQ group yesterday afternoon, and

folks were supportive of learning more about the code changes that would

be needed. After the meeting, Margaret Votava and a few others in our

group phoned Andrew Johnson to get his input on how we might most

constructively make such changes. Andrew mentioned that you've had

plans for some time for an upgrade that would allow users to specify

some amount of string or array buffering, and he suggested that we ask

you about that (and cc: core-talk). It's possible that our group could

contribute to that development, and we would like to understand the

scope. Do you have time to talk about this at some point?

Thanks,
Kurt

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System