RE: asynDriver - UDP server

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

Hi Joao,

 

The example in asyn/testAsynPortDriver is a simple example.

 

This tutorial starts with a simple driver and gets more complex in subsequent versions:

https://github.com/epics-modules/measComp/blob/master/documentation/measCompTutorial.pdf

 

This page has links to 2015 YouTube video lectures on asyn and asynPortDriver:

https://epics.anl.gov/docs/APS2015.php

 

This page also has links to 2018 YouTube videos on asyn and asynPortDriver under the areaDetector section:

https://www.bnl.gov/ps/epics/

 

Mark

 

 

From: Joao Afonso <joao.afonso@cern.ch>
Sent: Tuesday, December 4, 2018 8:44 AM
To: Mark Rivers <rivers@cars.uchicago.edu>
Cc: tech-talk@aps.anl.gov
Subject: RE: asynDriver - UDP server

 

Hi Mark,

 

Thank you for the quick answer.

I will take a look into asynPortDriver documentation, to see if writing a driver is a good approach for us.

 

Is there any specific documentation you would recommend to help writing it?

 

Thanks,

Joao

 

---

From: Mark Rivers [rivers@cars.uchicago.edu]
Sent: 03 December 2018 19:39
To: Joao Afonso
Cc: tech-talk@aps.anl.gov
Subject: RE: asynDriver - UDP server

Hi Joao,

 

What you have tried seems reasonable, but unfortunately it won’t work. The reason is that the drvAsynIPPort driver does not have a mechanism to asynchronously call back to device support when new input arrives.  There are several other ways to do this.

 

-       You can use streamDevice.  It works with SCAN=I/O Intr records by polling the device.  streamDevice should even be able to parse the UDP buffer for you into the individual records you want to use.

-       You could write your own little asyn driver, derived from asynPortDriver.  It would just have a small loop like this:

 

    while (1) {

        pasynOctet->read(myBuffer)

        value1 = parseMyBuffer(1)

        setIntegerParam(myParam1, value1)

        value2 = parseMyBuffer(2)

        setIntegerParam(myParam2, value2)

        callParamCallbacks()

    }

 

Mark

 

 

From: tech-talk-bounces@aps.anl.gov <tech-talk-bounces@aps.anl.gov> On Behalf Of Joao Afonso via Tech-talk
Sent: Monday, December 3, 2018 11:27 AM
To: tech-talk@aps.anl.gov
Subject: asynDriver - UDP server

 

Hello!

 

First, sorry if any of these questions seems too simple. I started working recently with EPICS and I am still learning how it works.

 

Basically, I am trying to create an IOC that works as a UDP server. It should be listening at a certain port and, when a new packet arrives, it should update a set of records with the incoming data.

It doesn't need to respond to any of the packets.

 

The data is a binary array, which will be read into a waveform record, and then unpacked into other records in order to be read by the clients (I don't know if this is the best approach, for now I am just experimenting). The structure of the binary array is fixed and known beforehand.

 

 

For now, I just want to update the waveform record with the binary data when the UDP packet arrives. I am using asynDriver since it seems to provide all the tools I need:

 

On the 'st.cmd' file I have:

 

[...]

drvAsynIPServerPortConfigure ("fgc_udp", "localhost:2906 udp", 10, 0, 0, 0)

dbLoadRecords("db/fgc_udp.db","GW=${FGC_GW_NAME}:")

[...]

 

And on the 'db/fgc_udp.db' I have:

 

record(waveform, "$(GW)UDP") {
     field(SCAN, "I/O Intr")
     field(DTYP, "asynOctetRead")
     field(FTVL, "UCHAR")
     field(DESC, "UDP publication")
     field(NELM, "4096")
     field(INP,  "@asyn(fgc_udp, 0, 0) drvUser")
 }

 

 

Since I am using 'I/O Intr', I would expect the record to be updated when a new UDP packet arrives, but it is not working.

It only updates if I use the IOC shell command "dbtr xxx:UDP", or if I change SCAN to a "N seconds" option.

 

Do you know how I can fix it? I guess it is something simple, but I am stuck.

 

I would also like to know if using a waveform record is a good starting point for unpacking binary data, or if there is a better alternative.

 

 

Thank you in advance,

Joao