Experimental Physics and
Industrial Control System

Mark Rivers via Tech-talk <[email protected]> · Mon, 23 Dec 2019 13:45:32 +0000

Hi Abdalla,

> scanOnce: Ring buffer overflow

?> For now I rarely get this message and the IOC is working fine, but what is the reason behind it?
> Could the record's IO is taking more time than the scan time?

That message is coming from dbScan.c in EPICS base.  It usually means that you have records with SCAN=I/O Intr that are processing very fast, i.e. lots of callbacks from your asyn driver.

There is a callback queue in EPICS base that is overflowing.   Since the problem is only happening every once in a while you can probably eliminate the message by increasing the size of the queue.  The queue size defaults to 2000.  You can check the current size with callbackShowQueue:

epics> callbackQueueShow
PRIORITY  HIGH-WATER MARK  ITEMS IN Q  Q SIZE  % USED  Q OVERFLOWS
   cbLow                7           0    2000     0.0            0
cbMedium                0           0    2000     0.0            0
  cbHigh                0           0    2000     0.0            0

You can increase the size to 5000 by adding this command to your IOC startup script before iocInit:

callbackSetQueueSize(5000)

Mark

________________________________
From: Tech-talk <[email protected]> on behalf of Abdalla Ahmad via Tech-talk <[email protected]>
Sent: Monday, December 23, 2019 12:44 AM
To: [email protected]
Subject: Ring buffer overflow

Hi

In an asyn port driver, I get the following message on the IOC shell

scanOnce: Ring buffer overflow

For now I rarely get this message and the IOC is working fine, but what is the reason behind it? Could the record's IO is taking more time than the scan time?

Best Regards,

Abdalla.

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System