[AsynPortDriver] "Multiple interrupt callbacks between processing" warning with multiple arrays

[Paweł Plewiński <pplewinski@dmcs.pl>]

Hi,

I've recently written asyn-based device support for a custom device 
communicating over PCIe. One of its functions is to periodically 
retrieve 4 waveforms from 4 channels, which is done in a separate 
thread, from which the callback function is called to notify asyn about 
change. I heavily based the code on the AsynPortDriver example.
The driver works, however if the update rate is lower than 1 second, 
strange warning appears in the console at the time of every refresh (and 
that's only for one of 4 channels), namely:
2017/04/11 15:42:08.682 PIEZO:OSC-CH0-WAVEFORM 
devAsynFloat64Array::interruptCallbackInput
\000\000\000\000\000@\205?\000\000\000\000\000\300\202?\000\000\000\000\000\000\204?\000\000\000\000\000\000\204?\000\000\000\000\000\300\202?\000\000\000\000\000\000\204?\000\000\000\000\000@\205?\000\000\000\000\000\000\204?\000\000\000\000\000\300\202?\000\000\000\000\000\000\204?
2017/04/11 15:42:08.682 PIEZO:OSC-CH0-WAVEFORM 
devAsynFloat64Array::processCommon, warning, multiple interrupt 
callbacks between processing
The parameters passed to the top level constructor are
   : asynPortDriver(portName,
                    4, /* maxAddr */
                    (int)NUM_SCOPE_PARAMS,
                    asynInt32Mask | asynFloat64Mask | 
asynFloat64ArrayMask | asynEnumMask | asynDrvUserMask, /* Interface mask 
*/
                    asynInt32Mask | asynFloat64Mask | 
asynFloat64ArrayMask | asynEnumMask,  /* Interrupt mask */
                    ASYN_MULTIDEVICE, /* asynFlags.  This driver does 
not block and it is not multi-device, so flag is 0 */
                    1, /* Autoconnect */
                    0, /* Default priority */
                    0) /* Default stack size*/

The readback thread code:

void piezoPortDriver::readbackTask(void)
{
   while (1) {
           bool stopped = false;

           lock();
           auto new_data = osc->fetch_data(vtim, vdat);
           unlock();

           if (!stopped)
           {
               lock();
               this->osc_update_trigger();
               unlock();
           }
        callParamCallbacks();

        for (int i = 0; i < 4; i++){
          doCallbacksFloat64Array(vdat[i].data(), vdat[i].size(), 
P_OscWaveform, i);
        }
        usleep(100000);
    }
}

The fetch_data method reads four 1000-element double vectors from PCIe.

Could you give me some suggestions what may be wrong?

Regards,
Paweł Plewiński
Department of Microelectronics and Computer Science
Lodz University of Technology