comedi_poll man page
comedi_poll — force updating of streaming buffer
int comedi_poll (comedi_t * device, unsigned int subdevice);
The function comedi_poll() is used on a subdevice that has a Comedi command in progress in order to update the streaming buffer. If supported by the driver, all available samples are copied to the streaming buffer. These samples may be pending in DMA buffers or device FIFOs. If sucessful, the number of additional bytes available is returned. If there is an error, -1 is returned.