Experimental Physics and
Industrial Control System

Tim Mooney <[email protected]> · Sun, 28 Nov 1999 17:49:43 -0600 (CST)

Mark, re...

> I am having intermittent problems which appear to be corruption of floating
> point operations.  It just occurred to me that perhaps the problem is because I
> am doing floating point operations in an interrupt service routine.  I am
> running vxWorks 5.3.1 on an MVME162 CPU.  Is one allowed to do floating point
> arithmetic in an interrupt service routine, or are the FP registers not saved
> and restored in interrupt routines?  Is there a compiler switch or directive
> to control this?

The floating point registers are not saved through interrupts.  They're
not even saved though task switches unless the task using them was
spawned with the option VX_FP_TASK.  You can save and restore them by
hand on entry to/exit from an interrupt handler by #include'ing ffpLib.h,
malloc'ing a context buffer, and calling fppSave(FP_CONTEXT *pContext)
and fppRestore(FP_CONTEXT *pContext).  BTW, you can't call malloc()
from interrupt level because it takes a semaphore.

I don't know of a compiler switch that makes saving FP registers the
default behavior.

Tim Mooney ([email protected]) (630)252-5417
Beamline Controls & Data Acquisition Group
Advanced Photon Source, Argonne National Lab

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System