Specifications

Comedi

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Description

The function comedi_get_hardcal_converter() initializes the comedi_polynomial_t pointed to by converter so it

can be passed to either comedi_to_physical(), or comedi_from_physical(). The result can 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().

This function initializes the comedi_polynomial_t pointed to by converter as a simple linear function with no calibration in-

formation, appropriate for boards which do their gain/offset/nonlinearity corrections in hardware. If your board needs calibration

to be performed in software by the host computer, use comedi_get_softcal_converter() instead. A subdevice will

advertise the fact that it depends on a software calibration with the SDF_SOFT_CALIBRATED subdevice ﬂag.

The result of this function will only depend on the channel parameter if either comedi_range_is_chan_specific() or

comedi_maxdata_is_chan_specific() returns true for the speciﬁed subdevice.

Return value

Returns 0 on success, -1 on failure.

5.4.3.6 comedi_get_softcal_converter

comedi_get_softcal_converter — get converter for software-calibrated subdevice

Synopsis

#include <comedilib.h>

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);

Status

alpha

Description

The function comedi_get_softcal_converter() initializes the comedi_polynomial_t pointed to by converter so it

can be passed to either comedi_to_physical() or comedi_from_physical(). The comedi_polynomial_t pointed to by

converter can then be used to convert data for 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 points to 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, the

calibration of a multiplexed analog input will typically not depend on the channel, only the range. 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 a polynomial 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.

Return value

Returns 0 on success, -1 on failure.