Re: IOC warning when connecting to 64 devices

[Mark Rivers via Tech-talk <tech-talk@aps.anl.gov>]

Hi Abdalla,

That is a fairly common problem when a lot of records are set to SCAN=I/O Intr and all process at iocInit.

The example startup script for areaDetector IOCs has this line at the end to prevent the ring buffer overflow:

callbackSetQueueSize(5000)

https://github.com/areaDetector/ADCore/blob/c73181f0a219af04c343f6bc41d108c77cca9764/iocBoot/EXAMPLE_commonPlugins.cmd#L221

Mark

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From: Tech-talk <tech-talk-bounces@aps.anl.gov> on behalf of Abdalla Ahmad via Tech-talk <tech-talk@aps.anl.gov>
Sent: Tuesday, May 6, 2025 2:47 AM
To: tech-talk@aps.anl.gov <Tech-talk@aps.anl.gov>
Subject: IOC warning when connecting to 64 devices

 

Hi

 

We developed an asyn port driver for a group of power supplies, 64 in total, controlled via Ethernet. When the IOC was developed to connect to all power supplies at once, I got the following warning:

 

callbackRequest: cbLow ring buffer full

 

The IOC became slow and could not handle processing some PVs at .1 second scan. I ended up splitting the main IOC into 4 IOCs each controlling 16 devices and the system is working fine. I would like to know more what causes this warning and is it possible to have 1 IOC controlling all 64 devices?

 

Best Regards,

Abdalla Al-Dalleh

Control Engineer

SESAME