Specifications

Comedi

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Description

Similar to comedi_data_read() except it will wait for the speciﬁed number of nanoseconds between setting the input channel

and taking a sample. For analog inputs, most boards have a single analog to digital converter which is multiplexed to be able to

read multiple channels. If the input is not allowed to settle after the multiplexer switches channels, the reading will be inaccurate.

This function is useful for allowing a multiplexed analog input to settle when switching channels.

Although the settling time is speciﬁed in nanoseconds, the actual settling time will be rounded up to the nearest microsecond.

5.4.1.5 comedi_data_read_hint

comedi_data_read_hint — tell driver which channel/range/aref you are going to read from next

Synopsis

#include <comedilib.h>

int comedi_data_read_hint(comedi_t * device, unsigned int subdevice, unsigned int channel, unsigned int range, unsigned int

aref);

Description

Used to prepare an analog input for a subsequent call to comedi_data_read(). It is not necessary to use this function, but it

can be useful for eliminating inaccuracies caused by insufﬁcient settling times when switching the channel or gain on an analog

input. This function sets an analog input to the channel, range, and aref speciﬁed but does not perform an actual analog to digital

conversion.

Alternatively, one can simply use comedi_data_read_delayed(), which sets up the input, pauses to allow settling, then

performs a conversion.

5.4.1.6 comedi_data_write

comedi_data_write — write single sample to channel

Synopsis

#include <comedilib.h>

int comedi_data_write(comedi_t * device, unsigned int subdevice, unsigned int channel, unsigned int range, unsigned int aref,

lsampl_t data);

Description

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.

Return value

On success, comedi_data_write() returns 1 (the number of samples written). If there is an error, -1 is returned.