Re: How fast can EPICS communicate with a device?

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

There is no limit in the speed of communicating with EPICS, only the speed of the link and the device latency.

How did you get SCAN=.01 second? Did you redefine the EPICS scan rates?

If you want to go as fast as possible you cannot use periodic scanning. You can use a set of FNLKs that for a loop or other mechanism to scan faster.

Are you using an asyn serial or IP port driver? If so you can turn in asynTrace to get time stamped messages to measure performance.

Mark


Sent from my iPhone

On Feb 15, 2019, at 8:05 AM, Sobhani, Bayan via Tech-talk <tech-talk@aps.anl.gov<mailto:tech-talk@aps.anl.gov>> wrote:

What exactly are the limitations on how fast EPICS can communicate with a device?

I have a device I can communicate with around 200Hz if I send it commands with a python program that uses the telnetlib module. I was wondering if it would be possible for the device to communicate with EPICS close to this rate.

I tried modify EPICS database definition files to make records process faster. To test this, I made a PV that does no device communication, but counts up when it was processed. When I added a line in the dbd file to add a scan option of .01 second, and set the SCAN field to .01, this record increases by 100 every second when I run the IOC, which is expected behavior.

However, when I tried having this record send commands to the device, it was much slower, around once per second. In general, when I process PVs that communicate with a device, it seems to take a while to get a response, whereas when I send commands directly through telnet I get the result back almost instantaneously.  Is there a limit to how fast EPICS can communicate with a device, apart from the SCAN field options?

Alex