Documentation/driver-api/generic-counter.rst

29 * Signal:
33   Association of a Signal, and evaluation trigger, with a Count.
38 SIGNAL  section in Theory
40 A Signal represents a stream of data. This is the input data that is
42 signal output line of a rotary encoder. Not all counter devices provide
43 user access to the Signal data, so exposure is optional for drivers.
45 When the Signal data is available for user access, the Generic Counter
46 interface provides the following available signal values:
49   Signal line is in a low state.
52   Signal line is in a high state.
54 A Signal may be associated with one or more Counts.
58 A Synapse represents the association of a Signal with a Count. Signal
62 The Synapse action mode specifies the Signal data condition that
68   Signal does not trigger the count function. In Pulse-Direction count
69   function mode, this Signal is evaluated as Direction.
88 A Synapse associates one Signal with one Count.
107   Rising edges on signal A updates the respective count. The input level
108   of signal B determines direction.
115     If direction is forward, rising edges on quadrature pair signal A
117     edges on quadrature pair signal A updates the respective count.
121     If direction is forward, rising edges on quadrature pair signal B
123     edges on quadrature pair signal B updates the respective count.
127     Any state transition on quadrature pair signal A updates the
131     Any state transition on quadrature pair signal B updates the
144 associated with a single Signal via a single Synapse. Take for example
148                 Count                Synapse        Signal
156 In this example, the Signal is a source input line with a pulsing
158 incremented. The Signal is associated with the respective Count via a
159 Synapse. The increase function is triggered by the Signal data condition
162 behavior is aptly represented by respective Count, Signal, and Synapse
166 A counter device is not limited to a single Signal; in fact, in theory
171                    Count                 Synapse     Signal
197                    Count                   Synapse      Signal
209 Only Signal A triggers the "Pulse-Direction" update function, but the
210 instantaneous state of Signal B is still required in order to know the
215 "None" condition action mode to indicate its respective Signal's
218 Keep in mind that the Signal, Synapse, and Count are abstract
253 respective Counter Signal associations (Synapses) made via
318 * Signal extensions are attributes that expose information/control
319   specific to a Signal. These types of attributes will exist under a
320   Signal's directory in sysfs.
322   For example, if you have an invert feature for a Signal, you can have
323   a Signal extension called "invert" that toggles that feature:
335   non-specific to a particular Count or Signal. This is where you would
524         | * Count 0              | * Signal 0             |
525         | * Count 1              | * Signal 0 Extension 0 |
526         | * Signal 3             | * Extension 4          |
528         | * Signal 5 Extension 0 | Channel 1              |
530         |                        | * Signal 4             |
531         |                        | * Signal 4 Extension 0 |
537 event channel 1 and execute the read callbacks for Signal 4, Signal 4