Re: CPP CA LINK's causing scanOnce to SUSPEND

[Nick Rees <n.rees@jach.hawaii.edu>]

All,

Some months ago (21 August, to be exact) I sent the following note to
tech-talk:

> It seems that in our system when an Analog Output record with SMSL
> closed_loop has its DOL link marked CPP and is linked to a PV on another
> crate, then if the other crate reboots the scanOnce task generates a
> floating point exception within the Ao record support routines and
> suspends.

I finally got a few hours to look at this and tracked it down to the fact
that the status was not being set bad in dbCaGetLink when the record
severity is being set to INVALID_ALARM (i.e. when the link drops). Since
the status is not bad, the record processes normally with an undefined
value in the VAL field, causing FPE's on RISC architectures. Having found
it, I am surprised that more people haven't stumbled on this.

The revised dbCaGetLink (in file dbCa.c), with the four lines added
highlighted by >>>>, is:

long dbCaGetLink(struct link *plink,short dbrType, char *pdest,
	unsigned short	*psevr,long *nelements)
{
    caLink		*pca = (caLink *)plink->value.pv_link.pvt;
    long		status = 0;
    long		(*pconvert)();
    STATUS		semStatus;
    short		link_action = 0;

    if(!pca) {
	errlogPrintf("dbCaGetLink: record %s pv_link.pvt is NULL\n",
		plink->value.pv_link.precord);
	return(-1);
    }
    semStatus = semTake(pca->lock,WAIT_FOREVER);
    if(semStatus!=OK) {
	errlogPrintf("dbCaGetLink: semStatus!OK\n");
	return(-1);
    }
    if(!pca->chid || ca_state(pca->chid) != cs_conn) {
	pca->sevr = INVALID_ALARM;
>>>>    status = -1;
	goto done;
    }
    if(!ca_read_access(pca->chid)) {
	pca->sevr = INVALID_ALARM;
>>>>    status = -1;
	goto done;
    }
    if((pca->dbrType == DBR_ENUM) && (dbDBRnewToDBRold[dbrType] == DBR_STRING)){
	/*Must ask server for DBR_STRING*/
	if(!pca->pgetString) {
	    plink->value.pv_link.pvlMask |= pvlOptInpString;
	    link_action |= CA_MONITOR_STRING;
	}
	if(!pca->gotInString) {
	    pca->sevr = INVALID_ALARM;
>>>>        status = -1;
	    goto done;
	}
	if(nelements) *nelements = 1;
	pconvert=dbFastGetConvertRoutine[dbDBRoldToDBFnew[DBR_STRING]][dbrType];
       	status = (*(pconvert))(pca->pgetString, pdest, 0);
	goto done;
    }
    if(!pca->pgetNative) {
	plink->value.pv_link.pvlMask |= pvlOptInpNative;
	link_action |= CA_MONITOR_NATIVE;
    }
    if(!pca->gotInNative){
	pca->sevr = INVALID_ALARM;
>>>>    status = -1;
	goto done;
    }
    if(!nelements || *nelements == 1){
	pconvert=
	    dbFastGetConvertRoutine[dbDBRoldToDBFnew[pca->dbrType]][dbrType];
       	(*(pconvert))(pca->pgetNative, pdest, 0);
    }else{
	unsigned long ntoget = *nelements;
	struct dbAddr	dbAddr;

	if(ntoget > pca->nelements)  ntoget = pca->nelements;
	*nelements = ntoget;
	pconvert = dbGetConvertRoutine[dbDBRoldToDBFnew[pca->dbrType]][dbrType];
	memset((void *)&dbAddr,0,sizeof(dbAddr));
	dbAddr.pfield = pca->pgetNative;
	/*Following will only be used for pca->dbrType == DBR_STRING*/
	dbAddr.field_size = MAX_STRING_SIZE;
	/*Ignore error return*/
	(*(pconvert))(&dbAddr,pdest,ntoget,ntoget,0);
    }
done:
    if(psevr) *psevr = pca->sevr;
    semGive(pca->lock);
    if(link_action) addAction(pca,link_action);
    return(status);
}


-- 
Nick Rees

Joint Astronomy Centre               Ph:       +1 (808) 961-3756
660 N. Aohoku Place                  Fax:      +1 (808) 961-6516
Hilo, HI.  96720                     Internet: n.rees@jach.hawaii.edu