modtcp channel status

[Eric Williams <ECWilliams@lbl.gov>]

We recently hooked up some Wago modules here to monitor some 
thermocouples through ethernet connections.  Since we were dealing with 
several isolated monitoring locations, one of the things I wanted in the 
driver was the ability to make sure the ethernet connection was intact 
through the EPICS channel status.  We're using the DESY modification of 
the TRIUMF modtcp driver 
(http://www-kryo.desy.de/documents/EPICS/DESY/Records/wagoModbusSup.html), 
and the driver did not show any change of status with a break in the 
TCP/IP connection, but some of the code appeared to show that the basic 
mechanism was already there.  Fiddling around with the code a bit, I 
came up with this mod:

In modtcpRead(), change the line:

   if (pPlc->pSock->tcpsFd == INVALID_SOCKET) return -1;

to:
   if (pPlc->pSock->connecting || pPlc->pSock->tcpsFd == 
INVALID_SOCKET) return -1;

Similarly change modtcpWrite().  The timeouts are long, but the record 
status does eventually go INVALID when the connection is lost, and then 
recovers when it is reestablished.
--
Eric Williams
ALS Controls
Lawrence Berkeley Lab