Specifications

Comedi

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Extended trigger conﬁguration should be designed in such a way that the user can probe for valid parameters, similar to how

command testing works. An extended trigger conﬁguration instruction should not conﬁgure the hardware directly, rather, the

conﬁguration should be saved until the subsequent command is issued. This allows more ﬂexibility for future interface changes.

It has not been decided whether the conﬁguration stage should return a token that is then used as the trigger argument in the

command. Using tokens is one method to satisfy the problem that extended trigger conﬁgurations may have subtle compatiblity

issues with other trigger sources/arguments that can only be determined at command test time. Passing all stages of a command

test should only be allowed with a properly conﬁgured extended trigger.

Extended triggers must use data[1] as ﬂags. The upper 16 bits are reserved and used only for ﬂags that are common to all

extended triggers. The lower 16 bits may be deﬁned by the particular type of extended trigger.

Various types of extended triggers must use data[1] to know which event the extended trigger will be assigned to in the command

structure. The possible values are an OR’d mask of the following:

• COMEDI_EV_START

• COMEDI_EV_SCAN_BEGIN

• COMEDI_EV_CONVERT

• COMEDI_EV_SCAN_END

• COMEDI_EV_STOP

4.7.5 Analog Triggering

(Status: alpha. The ni_mio_common.c driver implements this feature.)

The insn ﬁeld of the instruction data structure has not been assigned yet.

The chanspec ﬁeld of the instruction data structure is ignored.

The data ﬁeld of the instruction data structure is used as follows:

data[1] trigger and combining machine conﬁguration.

data[2] analog triggering signal chanspec.

data[3] primary analog level.

data[4] secondary analog level.

Analog triggering is described by a digital combining machine that has two sensitive digital inputs. The sensitive digital inputs

are generated by conﬁgurable analog comparators. The analog comparators generate a digital 1 when the analog triggering signal

is greater than the comparator level. The digital inputs are not modiﬁer inputs. Note, however, there is an effective modiﬁer due

to the restriction that the primary analog comparator level must be less than the secondary analog comparator level.

If only one analog comparator signal is used, the combining machine for the secondary input should be set to ignored, and the

secondary analog level should be set to 0.

The interpretation of the chanspec and voltage levels is device dependent, but should correspond to similar values of the analog

input subdevice, if possible.

Notes: Reading range information is not addressed. This makes it difﬁcult to convert comparator voltages to data values.

Possible extensions: A parameter that speciﬁes the necessary time that the set condition has to be true before the trigger is

generated. A parameter that speciﬁes the necessary time that the reset condition has to be true before the state machine is reset.