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Subject: RE: Strange asyn errors
From: "Mark Rivers" <rivers@cars.uchicago.edu>
To: <emmanuel_mayssat@lynceantech.com>, "EPICS tech-talk" <tech-talk@aps.anl.gov>
Date: Thu, 3 Mar 2011 18:26:41 -0600
Those errors happen under the following circumstances:

- You have an input record that is I/O Intr scanned.
- The callbacks from the driver are happening faster than the record
processing can keep up with.

Standard asyn device support for I/O scanned records uses a ring buffer
with a default size of 10 values for driver callbacks.  This allows it
to handle short bursts of callbacks without losing values.  However, if
the callbacks continue to arrive too fast then the ring buffer
overflows, and it discards values and prints that warning.

Prior to asyn R4-13 the new value was discarded.  In R4-13 this was
changed so that the oldest value was discarded and the new value put
into the ring buffer.  This means that when a burst stops the record
value is guaranteed to contain the last value from the driver.

Mark


-----Original Message-----
From: tech-talk-bounces@aps.anl.gov
[mailto:tech-talk-bounces@aps.anl.gov] On Behalf Of
emmanuel_mayssat@lynceantech.com
Sent: Thursday, March 03, 2011 5:37 PM
To: EPICS tech-talk
Subject: Strange asyn errors


Hello,

I have an embedded IOC (ts7370) that runs an asyn driver.
That ioc is renning a seq sequence for data acquisition.
The acquisition should go as fast as possible.

I try to optimize the processing speed.
but from the asyn driver I get the following errors occasionally.
What do they mean?
How to fix them ?

[...]
2011/03/03 23:37:13.889 TS7000:1:6:BI devAsynInt32 getCallbackValue
error, 4 ring buffer
overflows
2011/03/03 23:37:13.890 TS7000:1:7:BI devAsynInt32 getCallbackValue
error, 4 ring buffer
overflows
2011/03/03 23:37:13.892 TS7000:1:1:AI devAsynFloat64 getCallbackValue
error, 4 ring buffer
overflows
2011/03/03 23:37:13.895 TS7000:1:1:PrmptLngthLI devAsynFloat64
getCallbackValue error, 4
ring buffer overflows
2011/03/03 23:37:13.897 TS7000:1:1:PrmptRawAvrgLI devAsynFloat64
getCallbackValue error, 4
ring buffer overflows
[...]


Thanks,


-- 
Emmanuel


References:
Strange asyn errors emmanuel_mayssat

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