Experimental Physics and
Industrial Control System

Marty Kraimer <[email protected]> · Mon, 30 Jun 1997 08:33:42 -0500

Ralph Lange wrote:
> 
> Hi all -
> 
> While we're sitting at our test stand again trying to reproduce the IOC's
> crashes, we think we have thought of a scenario where the onceQ is getting
> filled with crap without some faulty driver or device support doing weird
> things.
> 
> [First of all: During the last week I have learned *a lot* about CA and the
> database by reading the sources and found a couple of things and thoughts
> in the concept and design really amazing.]
> 
> We found that the crap in the onceQ looked like as if a rngBufPut() call
> was interrupted by itself.
> 
> This is an excerpt from the onceQ buffer:
> 
> 00e3e010:  00f7941c 00f7941c 00f7941c 00f7941c   *................*
> 00e3e020:  00f7941c 00f7941c 00f7941c 00f7941c   *................*
> 00e3e030:  f7941c00 f7941c00 f7941c00 f7941c00   *................*
> 00e3e040:  941c00f7 941c00f7 941c00f7 941c00f7   *................*
> 00e3e050:  941c00f7 1c00f794 1c00f794 1c00f794   *................*
> 00e3e060:  1c00f794 1c00f794 1c00f794 00f7941c   *................*
> 
> 00f7941c is a valid record pointer. Do you see how bytes get swallowed from
> time to time?
> 
> This is what we think is happening: [I'm giving more details than necessary
> to give you the chance to find exactly the point where we are wrong ...;-]
> 
> scanOnce() is the only function that writes into the onceQ.
> 
> The onceQ is not guarded by a mutex semaphore, so interruption of
> scanOnce() must be impossible by means of design.

It looks like you have found a bug. I will hang my head in shame!!

> Solution: Guarding the onceQ with a binary semaphore.

I would rather keep the option of calling scanOnce from interrupt level.
I think it is better to use intLock/intUnlock.
This is what callback does so that callbackRequest
can be called from interupt routines.

Thus scanOnce should be:

 void scanOnce(void *precord)
{
    static int newOverflow=TRUE;
    int lockKey;
    int nput;

    lockKey = intLock();
    nput = rngBufPut(onceQ,(void *)&precord,sizeof(precord));
    intUnlock(lockKey);
    if(nput!=sizeof(precord)) {
        if(newOverflow)errMessage(0,"rngBufPut overflow in scanOnce");
        newOverflow = FALSE;
    }else {
        newOverflow = TRUE;
    }
    semGive(onceSem);
}

This will be in next beta release.

> What are we missing?

Nothing!!!

THANKS.

By the way let us know if your problem goes away.

Also keep looking at code. We really really appreciate your
finding problems.

Martyu Kraimer

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System