Specifications

Comedi

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Comedi instructions are described by the comedi_insn structure. Applications send instructions to the driver in order to perform

control and measurement operations that are done immediately or synchronously, i.e., the operations complete before program

control returns to the application. In particular, instructions cannot describe acquisition that involves timers or external events.

The ﬁeld insn determines the type of instruction that is sent to the driver. Valid instruction types are:

INSN_READ read values from an input channel

INSN_WRITE write values to an output channel

INSN_BITS read/write values on multiple digital I/O channels

INSN_CONFIG conﬁgure a subdevice

INSN_GTOD read a timestamp, identical to gettimeofday() except the seconds and microseconds values are of type

lsampl_t.

INSN_WAIT wait a speciﬁed number of nanoseconds

The number of samples to read or write, or the size of the conﬁguration structure is speciﬁed by the ﬁeld n, and the buffer for

those samples by data. The ﬁeld subdev is the subdevice index that the instruction is sent to. The ﬁeld chanspec speciﬁes the

channel, range, and analog reference (if applicable).

Instructions can be sent to drivers using comedi_do_insn(). Multiple instructions can be sent to drivers in the same system

call using comedi_do_insnlist().

5.3.9 comedi_range

typedef struct comedi_range_struct comedi_range;

struct comedi_range_struct{

double min;

double max;

unsigned int unit;

}comedi_range;

The comedi_range structure conveys part of the information necessary to translate sample values to physical units, in particular,

the endpoints of the range and the physical unit type. The physical unit type is speciﬁed by the ﬁeld unit, which may take the

values UNIT_volt for volts, UNIT_mA for milliamps, or UNIT_none for unitless. The endpoints are speciﬁed by the ﬁelds

min and max.

5.3.10 comedi_krange

typedef struct comedi_krange_struct comedi_krange;

struct comedi_krange_struct{

int min;

int max;

unsigned int flags;

};

The comedi_krange structure is used to transfer range information between the driver and Comedilib, and should not normally

be used by applications. The structure conveys the same information as the comedi_range structure, except the ﬁelds min and

max are integers, multiplied by a factor of 1000000 compared to the counterparts in comedi_range.

In addition, kcomedilib uses the comedi_krange structure in place of the comedi_range structure.