RE: Packed Data Message Formats With Fixed-Length Strings

["Mooney, Tim M." <mooney@aps.anl.gov>]

Hi Iain,

I think I would do this with an aSub record: read the input into a waveform record; configure an aSub record input to be an array of char, and point the input link at the waveform record's VAL field; and write an aSub routine to parse it.

Tim Mooney (mooney@aps.anl.gov) (630)252-5417
Beamline Controls Group (www.aps.anl.gov)
Advanced Photon Source, Argonne National Lab


________________________________________
From: tech-talk-bounces@aps.anl.gov [tech-talk-bounces@aps.anl.gov] on behalf of Iain Marcuson [Iain.Marcuson@sydorinstruments.com]
Sent: Tuesday, November 08, 2016 10:46 AM
To: tech-talk@aps.anl.gov
Subject: Packed Data Message Formats With Fixed-Length Strings

I am writing EPICS code to interface with a custom device.  The device protocol is fixed-length messages.  I can read and write the message parameters with Stream Device, and have done so successfully except for the fixed-length string, which I have had to bypass in assorted ways.

The output command message has the Python struct format "ii128s12i".  The input message has the Python struct format "128s12ii".  The "12i" refers to 12 parameters, passed or returned.

My two questions are:

1) How can I parse the fixed-length string?  The normal string-handling routines fail either because of terminator characters in the string or because the string is two long.
2) I handle the parameters by having a PV for each parameter, and a separate "group" of PVs for each command.  Is this best practice?

Thank you,

Iain Marcuson.