comedi_get_softcal_converter man page
comedi_get_softcal_converter — get converter for software-calibrated subdevice
int comedi_get_softcal_converter (unsigned subdevice, unsigned channel, unsigned range, enum comedi_conversion_direction direction, const comedi_calibration_t *parsed_calibration, comedi_polynomial_t *converter);
comedi_get_softcal_converter() initializes converter so it can be passed to either comedi_to_physical() or comedi_from_physical(). The converter parameter can then be used to convert data from the specified subdevice, channel, and range. The direction parameter specifies whether converter will be passed to comedi_to_physical() or comedi_from_physical(). The parsed_calibration parameter contains the software calibration values for your device, and may be obtained by calling comedi_parse_calibration_file() on a calibration file generated by the comedi_soft_calibrate program.
This function is only useful for boards that perform their calibrations in software on the host computer. A subdevice will advertise the fact that it depends on a software calibration with the SDF_SOFT_CALIBRATED subdevice flag.
Whether or not the result of this function actually depends on the channel parameter is hardware dependent. For example, a multiplexed analog input will typically use the same calibration for all input channels. Analog outputs will typically use different calibrations for each output channel.
Software calibrations are implemented as polynomials (up to third order). Since the inverse of polynomials of order higher than one can't be represented exactly as another polynomial, you may not be able to get converters for the "reverse" direction. For example, you may be able to get a converter for an analog input in the COMEDI_TO_PHYSICAL direction, but not in the COMEDI_FROM_PHYSICAL direction.
Zero on success or -1 on failure.