Experimental Physics and
Industrial Control System

Timo Korhonen <[email protected]> · Tue, 31 Aug 1999 09:27:27 +0200

Hi,

Andrew Johnson's message to Power PC sites prompted me to ask a question
which
has been nagging me a while but I have not yet had a chance to dig into it to
find the real answer.

We noticed a curious problem when porting the OMS58 motor control card
drivers to ppc.
(drvOms58, drvOmsCom from APS, Thomas Coleman is the current author,
I believe)
On a mv167 it worked fine, but when running on our ppc card (Motorola
mvme2306), the
motor position was not correctly read back.
The driver works by spawning a task (tmotor) which handles message traffic
and status queries.
After a couple days of confusion and a number of attempts I was able to track
down our problem to a point
where the motor task was supposed to call a routine that requests a data area
update (i.e. requests
the DSP on the oms58 card to report the current motor status).  This routine
was not called where it should
have been. The pointer to this subroutine is passed to the motor task in a
structure, and the subroutine
was declared as

STATIC void start_status(int card);

I removed the STATIC keyword, recompiled and the motor started to work. We
have been using it after that
and have so far not seen any problems.

I also had a similar problem with GPIB support (we are using the HPE2050 LAN
gateway support
from Benjamin Franksen at BESSY) when porting device support modules.  When I
removed the "static"
keyword in devGpib.h :
/*static*/ struct devGpibParmBlock devSupParms;
the drivers started to work. When declared static, the data that was supposed
to be in the structure was
not correctly passed from the init routine to the records.

These changes seemed to work, but does somebody have an explanation why?
On the other hand, this seems sort of logical because static variables are
valid only within a program
unit (according to my textbook), but why does this then work with a 68k cpu?

I will submit the full patches (diffs) if people agree that these changes
make sense. Or is there a better way to fix this problem?

Timo

--
Timo Korhonen  PSI (Paul Scherrer Institut), SLS
               CH-5232 Villigen PSI
               tel + 41- 56 3103262  fax + 41 - 56 310 4413
e-mail:        [email protected]

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System