Re: Waveform VAL fields in newer versions of EPICS

[Michael Davidsaver via Tech-talk <tech-talk@aps.anl.gov>]

Hi Scott,

On 10/7/25 16:19, Baily, Scott A via Tech-talk wrote:

In EPICS 3.14.12 IOCs running the command dba <waveformrecordname> returned a field address that was the same as the BPTR field of the waveform record.

In EPICS 3.15.9 and epics 7, this is no longer the case.  The dba command gets its information by calling dbNameToAddr as is proper for an SPC_DBADDR field, this should give the actual location of the VAL field contents.  In 3.14.12 this address is also stored in the BPTR field.  It appears that dbNameToAddr no longer results in paddr->pfield pointing to the contents of the VAL field.  Is this expected behavior? If so, how should one obtain the contents of SPC_DBADDR field? I assume this is available (for this specific case) if BPTR were directly referenced, but this doesn’t seem like the proper method. 

In general, I would recommend looking to dbGet() / dbPut() as the canonical examples of how to interact with dbAddr.  Beginning with 3.15.0.1, it became allowed for a rset::get_array_info callback to modify dbAddr::pfield.

   /* Update field info from record (if necessary);
     * may modify paddr->pfield.
     */
    if (!dbfl_has_copy(pfl) &&
        paddr->pfldDes->special == SPC_DBADDR &&
        (prset = dbGetRset(paddr)) &&
        prset->get_array_info) {
        status = prset->get_array_info(paddr, &no_elements, &offset);

https ://github.com/epics-base/epics-base/blob/7444936a22c00a8776f3bba9bed84acf91801b1c/modules/database/src/ioc/db/dbAccess.c#L932-L939

An example from aaiRecord.c

static long get_array_info(DBADDR *paddr, long *no_elements, long *offset)
{
    aaiRecord *prec = (aaiRecord *)paddr->precord;

    paddr->pfield = prec->bptr;
    *no_elements =  prec->nord;
    *offset = 0;
    return 0;
}

https ://github.com/epics-base/epics-base/blob/7444936a22c00a8776f3bba9bed84acf91801b1c/modules/database/src/std/rec/aaiRecord.c#L221