comedi_data_write man page
comedi_data_write — write single sample to channel
int comedi_data_write (comedi_t * device, unsigned int subdevice, unsigned int channel, unsigned int range, unsigned int aref, lsampl_t data);
Writes a single sample on the channel that is specified by the Comedi device device, the subdevice subdevice, and the channel channel. If appropriate, the device is configured to use range specification range and analog reference type aref. Analog reference types that are not supported by the device are silently ignored.
The function comedi_data_write() writes the data value specified by the parameter data to the specified channel.
On sucess, comedi_data_write() returns 1 (the number of samples written). If there is an error, -1 is returned.