Experimental Physics and
Industrial Control System

Chip Watson <[email protected]> · Thu, 24 Aug 2000 15:04:09 -0400

There is a bug in the interaction of channel access and the IOC which
only appears under unusual circumstances, but was stumbled into by CDEV
code. The problem appeared when CDEV version 1.7.2 attempted to
get the HOPR / LOPR field of a CALC record.  (IOC running 3.13) The
following was observed on the IOC at SLS:

    Floating point overflow
    Floating point inexact
    Exception current instruction address: 0x01a60838
    Machine Status Register: 0x0010b130
    Condition Register: 0x22000040
    Fp Control and Status Register: 0xd2028070
    Task: 0x18f0560 "CA client"
    filename="../taskwd.c" line number=175
    task 18f0560 CA client suspended

I chased the problem back to exactly what CA client code causes this
event and found that it comes from asking for the DBR_CNTL_FLOAT
for the calc record.HOPR channel.  This is of course an unusual thing to ask
for, but happens if a slider (for example) is attached to the HOPR field of
a CALC record using CDEV.

In the meantime, we have patched the CDEV client code at PSI / SLS
to not make this type of call (unless forced to by the caller) to avoid this
problem.  These mods will be included in CDEV 1.7.3, but can be obtained
sooner if anyone else has experienced this problem.

--
Chip Watson
High Performance Computing Group
Thomas Jefferson National Accelerator Facility
Tel: (757) 269-7101
http://www.jlab.org/~watson

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System