int comedi_do_insn (comedi_t * device, comedi_insn * instruction);
The function comedi_do_insn() performs a single instruction. If sucessful, comedi_do_insn() returns the number of samples measured, which may be less than the number of requested samples. Comedi limits the number of requested samples in order to enforce fairness among processes. If there is an error, -1 is returned.