Experimental Physics and
Industrial Control System

"Jeff Hill" <[email protected]> · Wed, 9 Feb 2005 08:13:42 -0700

Dirk,

I don't know if anyone has made this suggestion, but
watch out for a driver that uses floating point in its
interrupt service routines as, on vxWorks, the FP
register contents are not saved / restored when entering
/ exiting interrupt context. The driver must do this
manually if it finds a need to use FP in its ISR.

Jeff

> -----Original Message-----
> From: Dirk Zimoch [mailto:[email protected]]
> Sent: Tuesday, February 08, 2005 5:51 AM
> To: TECHTALK
> Subject: compiler bug in gcc version 2.8.1 (Tornado1)
> for PPC corrupts floationg point constants?
> 
> Hi all,
> 
> I have some driver software that contains
> 
> double scan_period;
> scan_period = 0.05;
> 
> The function is executed from startup script, i.e. the
> executing task is
> a floating point task.
> 
> However, sometimes when booting R3.13.2, the ioc
> crashes with "floating
> point underflow" while executing
> 
> printf ("init_record_generic: scan_period=%f\n",
> scan_period);
> 
> I couldn't even look at the registers, because ti also
> crashes when it
> tries to print the register containing scan_period.
> 
> According to the bitpattern, scan_period is not 0.05,
> but some
> denormalized value.
> 
> Even more astonishing is that the error only happens
> sometimes! In rare
> cases, everything is OK. When I boot R3.13.5, also
> everything is OK. I
> have compared the driver library compiled for both
> EPICS versions. It is
> exactly the same object code.
> 
> We load the driver library in the startup script.
> Maybe there is
> something wrong with the ld command, corrupting
> constants?
> 
> But how can this depend on the EPICS release? Maybe
> the code is loaded
> to another location, but does the location matter?
> 
> Why does this only happen with one driver?
> 
> Any ideas or solutions?
> 
> 
> Dirk
> 
> --
> Dr. Dirk Zimoch
> Swiss Light Source
> Paul Scherrer Institut
> Computing and Controls
> phone +41 56 310 5182
> fax   +41 56 310 4413

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System