Experimental Physics and
Industrial Control System

Eric Williams <[email protected]> · Thu, 26 Aug 2004 14:54:24 -0700

I just thought I'd throw this solution out so it would be in the
archives if someone else needed it.
We have a RS-232 device we wanted to control with EPICS (a Thales Optem
zoom lens control stepping motor drive) that reported its status on a
continuous basis. The IOC was a Linux box running 3.14 with the
GpibCore driver used to talk to the serial port. 
Because the device didn't wait for a command but instead sent its status
periodically, the serial port's input buffer would fill up and cause
GpibCore to get an error and dump EPICS as soon as you tried to process
any of the records going to the device's port. I thought about digging
into the driver and making it more tolerant of babbling devices, but
abandoned that idea in favor of an easier solution.
I built a filter daemon which would open the serial port to the device
and pick up the input stream, decode the status, and store it locally.
The other side of the filter was through a pseudo-tty which emulated the
device's command set, passing on commands to the device, but with the
addition of a new command to read the local copy of the current status.
This daemon ran in the background, and the GpibCore driver would talk to
the pseudo-tty port instead of the serial port. The daemon was
auto-started through the standard Linux init mechanisms.

--

Eric Williams

Advance Light Source

Lawrence Berkeley Lab

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System