This chapter is meant to be a reference for some of the advanced
features of Comedi.
+<sect1>Digital input combining machines
+
+<p>
+When one or several digital inputs are used to modify an output
+value, either an accumulator or a single digital line or bit,
+a bitfield structure is typically used in the Comedi interface.
+The digital inputs have two properties, "sensitive" inputs and
+"modifier" inputs. Edge transitions on sensitive inputs cause
+changes in the output signal, whereas modifier inputs change the
+effect of edge transitions on sensitive inputs. Note that inputs
+can be both modifier inputs and sensitive inputs.
+
+<p>
+For simplification purposes, it is assumed that multiple digital
+inputs do not change simultaneously.
+
+<p>
+The combined state of the modifier inputs determine a modifier
+state. For each combination of modifier state and sensitive
+input, there is a set of bits that determine the effect on the
+output value due to positive or negative transitions of the
+sensitive input. For each transition direction, there are two
+bits defined as follows:
+
+<itemize>
+<item>00 - transition is ignored
+<item>01 - accumulator is incremented, or output is set
+<item>10 - accumulator is decremented, or output is cleared
+<item>11 - reserved
+</itemize>
+
+<p>
+For example, a simple digital follower is specified by the bit
+pattern 01 10, because it sets the output on positive transitions
+of the input, and clears the output on negative transitions. A
+digital inverter is similarily 10 01. These systems have only
+one sensitive input.
+
+<p>
+As another example, a simple up counter, which increments on
+positive transitions of one input, is specified by 01 00. This
+system has only one sensitive input.
+
+<p>
+When multiple digital inputs are used, the inputs are divided
+into two types, inputs which cause changes in the accumulator, and
+those that only modify the meaning of transitions on other inputs.
+Modifier inputs do not require bitfields, but there needs to be
+a bitfield of length 4*(2^(N-1)) for each edge sensitive input,
+where N is the total number of inputs. Since N is usually 2 or
+3, with only one edge sensitive input, the scaling issues are
+not significant.
+
+
+
<sect1>INSN_CONFIG
<p>
<sect2>Extended Triggering
-<p>Status: design
+<p>Status: alpha
<p>ID: not assigned
-<p>CHanspec: ignored
+<p>Chanspec: ignored
<p>
This section covers common information for all extended
command test time. Passing all stages of a command test should
only be allowed with a properly configured extended trigger.
+<p>
+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.
+
<p>
Various types of extended triggers must use data[1] to know which
event the extended trigger will be assigned to in the command
<item>COMEDI_EV_STOP
</itemize>
-<p>
-Extended triggers must use data[2] 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.
-
-<p>
-Notes: data[1] and data[2] may eventually be combined.
<sect2>Analog Triggering
-<p>Status: design
+<p>Status: alpha
<p>ID: not assigned
+<p>Implementation: ni_mio_common
<p>Chanspec: ignored
+<itemize>
+<item>data[1] - trigger and combining machine configuration
+<item>data[2] - analog triggering signal chanspec
+<item>data[3] - primary analog level
+<item>data[4] - secondary analog level
+</itemize>
+
+<p>
+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.
+
<p>
-Analog triggering is described by a state machine that has two
-states, "set" and "reset". Transitions from the reset state to
-the set state cause a trigger to be issued. The state machine is
-configured by specifying the chanspec
-for the analog line to trigger on (data[3]), the voltage level that
-resets the trigger (data[4]), and the voltage level that sets the
-trigger (data[5]). The interpretation of the chanspec and voltage
-levels is device dependent, but should correspond to similar values
-of the analog input subdevice, if relevant.
+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.
<p>
-If the set voltage is greater than the reset voltage, it is
-assumed that any voltage greater than the set voltage is sufficient
-for the set condition, and any voltage lesser than the reset voltage
-is sufficient for the reset condition.
+The interpretation of the chanspec and voltage levels is device
+dependent, but should correspond to similar values of the analog
+input subdevice, if possible.
<p>
Notes: Reading range information is not addressed. This makes it
-difficult to convert voltages to data values. A simple
-set/reset model may not be sufficient to describe all analog triggers.
-In particular, this doesn't properly describe analog triggering that
-operates when the input voltage is within some range, but not greater
-or lesser than the range.
+difficult to convert comparator voltages to data values.
<p>
Possible extensions: A parameter that specifies the necessary time
has to be true before the state machine is reset.
-<sect2>Pattern Matching Triggering
+<sect2>Bitfield Pattern Matching Extended Trigger
<p>Status: design
<p>ID: not assigned
<p>Chanspec: ignored
+<itemize>
+<item>data[1] - trigger flags
+<item>data[2] - mask
+<item>data[3] - pattern
+</itemize>
+
<p>
The pattern matching trigger issues a trigger when all of a specifed
set of input lines match a specified pattern. If the device allows,
the input lines should correspond to the input lines of a digital input
subdevice, however, this will necessarily be device dependent. Each
possible digital line that can be matched is assigned a bit in the
-mask and pattern. A bit set in the mask (data[3]) indicates that the
-input line must match the corresponding bit in the pattern (data[4]).
+mask and pattern. A bit set in the mask indicates that the
+input line must match the corresponding bit in the pattern.
A bit cleared in the mask indicates that the input line is ignored.
<p>
too few. Devices may support selecting different sets of lines from
which to match a pattern.
+<p>
+Discovery: The number of bits can be discovered by setting the mask
+to all 1's. The driver must modify this value and return -EAGAIN.
+
<sect2>Counter configuration
<p>ID: not assigned
<p>Chanspec: used to specify counter
+<itemize>
+<item>data[1] - trigger configuration
+<item>data[2] - primary input chanspec
+<item>data[3] - primary combining machine configuration
+<item>data[4] - secondary input chanspec
+<item>data[5] - secondary combining machine configuration
+<item>data[6] - latch configuration
+</itemize>
+
<p>
Counters can be operated either in synchronous mode (using insn_read)
or asynchronous mode (using commands), similar to analog input subdevices.
+The input signal for both modes is the accumulator.
Commands on counter subdevices are almost always specified using
scan_begin_src=TRIG_OTHER, with the counter configuration also serving
as the extended configuration for the scan begin source.
<p>
-Counters are made up of an accumulator and a state machine that
+Counters are made up of an accumulator and a combining machine that
determines when the accumulator should be incremented or decremented
-based on the values of the input signals. The state machine
+based on the values of the input signals. The combining machine
optionally determines when the accumulator should be latched and
-put into a buffer.
+put into a buffer. This feature is used in asynchronous mode.
<p>
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