From b08c118cde9dfd92f1f3c90544a682ee8b2ea740 Mon Sep 17 00:00:00 2001 From: Dmitry Torokhov Date: Thu, 6 Apr 2017 18:08:42 -0700 Subject: Input: docs - split input docs into kernel- and user-facing Split input documentation into several groups: kernel- and user-facing, and notes about individual device drivers. Move device drivers docs into a separate subdirectory. Signed-off-by: Dmitry Torokhov --- Documentation/input/devices/rotary-encoder.rst | 131 +++++++++++++++++++++++++ 1 file changed, 131 insertions(+) create mode 100644 Documentation/input/devices/rotary-encoder.rst (limited to 'Documentation/input/devices/rotary-encoder.rst') diff --git a/Documentation/input/devices/rotary-encoder.rst b/Documentation/input/devices/rotary-encoder.rst new file mode 100644 index 000000000000..b07b20a295ac --- /dev/null +++ b/Documentation/input/devices/rotary-encoder.rst @@ -0,0 +1,131 @@ +============================================================ +rotary-encoder - a generic driver for GPIO connected devices +============================================================ + +:Author: Daniel Mack , Feb 2009 + +Function +-------- + +Rotary encoders are devices which are connected to the CPU or other +peripherals with two wires. The outputs are phase-shifted by 90 degrees +and by triggering on falling and rising edges, the turn direction can +be determined. + +Some encoders have both outputs low in stable states, others also have +a stable state with both outputs high (half-period mode) and some have +a stable state in all steps (quarter-period mode). + +The phase diagram of these two outputs look like this:: + + _____ _____ _____ + | | | | | | + Channel A ____| |_____| |_____| |____ + + : : : : : : : : : : : : + __ _____ _____ _____ + | | | | | | | + Channel B |_____| |_____| |_____| |__ + + : : : : : : : : : : : : + Event a b c d a b c d a b c d + + |<-------->| + one step + + |<-->| + one step (half-period mode) + + |<>| + one step (quarter-period mode) + +For more information, please see + https://en.wikipedia.org/wiki/Rotary_encoder + + +Events / state machine +---------------------- + +In half-period mode, state a) and c) above are used to determine the +rotational direction based on the last stable state. Events are reported in +states b) and d) given that the new stable state is different from the last +(i.e. the rotation was not reversed half-way). + +Otherwise, the following apply: + +a) Rising edge on channel A, channel B in low state + This state is used to recognize a clockwise turn + +b) Rising edge on channel B, channel A in high state + When entering this state, the encoder is put into 'armed' state, + meaning that there it has seen half the way of a one-step transition. + +c) Falling edge on channel A, channel B in high state + This state is used to recognize a counter-clockwise turn + +d) Falling edge on channel B, channel A in low state + Parking position. If the encoder enters this state, a full transition + should have happened, unless it flipped back on half the way. The + 'armed' state tells us about that. + +Platform requirements +--------------------- + +As there is no hardware dependent call in this driver, the platform it is +used with must support gpiolib. Another requirement is that IRQs must be +able to fire on both edges. + + +Board integration +----------------- + +To use this driver in your system, register a platform_device with the +name 'rotary-encoder' and associate the IRQs and some specific platform +data with it. Because the driver uses generic device properties, this can +be done either via device tree, ACPI, or using static board files, like in +example below: + +:: + + /* board support file example */ + + #include + #include + #include + + #define GPIO_ROTARY_A 1 + #define GPIO_ROTARY_B 2 + + static struct gpiod_lookup_table rotary_encoder_gpios = { + .dev_id = "rotary-encoder.0", + .table = { + GPIO_LOOKUP_IDX("gpio-0", + GPIO_ROTARY_A, NULL, 0, GPIO_ACTIVE_LOW), + GPIO_LOOKUP_IDX("gpio-0", + GPIO_ROTARY_B, NULL, 1, GPIO_ACTIVE_HIGH), + { }, + }, + }; + + static const struct property_entry rotary_encoder_properties[] __initconst = { + PROPERTY_ENTRY_INTEGER("rotary-encoder,steps-per-period", u32, 24), + PROPERTY_ENTRY_INTEGER("linux,axis", u32, ABS_X), + PROPERTY_ENTRY_INTEGER("rotary-encoder,relative_axis", u32, 0), + { }, + }; + + static struct platform_device rotary_encoder_device = { + .name = "rotary-encoder", + .id = 0, + }; + + ... + + gpiod_add_lookup_table(&rotary_encoder_gpios); + device_add_properties(&rotary_encoder_device, rotary_encoder_properties); + platform_device_register(&rotary_encoder_device); + + ... + +Please consult device tree binding documentation to see all properties +supported by the driver. -- cgit v1.2.3