Re: Fetching return value from external program call in StreamDevice

[Dirk Zimoch <dirk.zimoch@psi.ch>]

Hi Christian

At the moment, StreamDevice cannot do this directly. The 'exec' command 
can only pass parameters to an external program but cannot pipe data 
into the program or read its output, nor can it evaluate the exit status.

But it would be a nice exercise to write an asynOctet driver that uses a 
piped program instead of a serial line.

drvAsynPipeConfigure "myProgramPort" "program arg1 arg2 arg3 ..."

The driver may restart the program whenever it has exited and asyn tries 
to talk to the port again (i.e. autoConnect).

Any volunteers?

Dirk

On 05.02.2015 17:58, Christian Pauly wrote:
> Hi
>
> I want to read out a little pressure sensor, for which i have already a
> small python script which reads the sensor (via i2c bus) and prints the
> sensor value to the terminal. Alternatively, i could also give the
> sensor value as return value upon program exit.
>
>
> Now i want to read this sensor inside an EPICS IOC.
> Is it possible, to use StreamDevice for this, by calling the external
> script / program and evaluating the return value ?
> Maybe using the "exec" statement in the protocol file ?
>
> Reading the sensor takes some time (500ms), so it would be good to do it
> asynchronously, without blocking the IOC.
>
> Or is there any other easy way, without reimplementing all the i2c
> sensor readout eg inside an ASYN driver in C++ code ?
>
>
> Thanks for any hints or help
>
> Best regards,
> Christian