Re: How fast can EPICS communicate with a device?

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

Sorry I missed that you added .01 second in the dbd file, so ignore that question.

I suspect you are getting a timeout if you only get 1 Hz. Turn on asynTrace to see what is happening on the communication link.

What device support are you using? StreamDevice, asyn device support, etc.?

Mark

Sent from my iPhone

> On Feb 15, 2019, at 8:20 AM, Mark Rivers via Tech-talk <tech-talk@aps.anl.gov> wrote:
> 
> 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