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Diffstat (limited to 'Documentation/input/rotary-encoder.txt')
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diff --git a/Documentation/input/rotary-encoder.txt b/Documentation/input/rotary-encoder.txt deleted file mode 100644 index 46a74f0c551a..000000000000 --- a/Documentation/input/rotary-encoder.txt +++ /dev/null @@ -1,126 +0,0 @@ -rotary-encoder - a generic driver for GPIO connected devices -Daniel Mack <daniel@caiaq.de>, Feb 2009 - -0. 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 - - -1. 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. - -2. 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. - - -3. 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. - -struct rotary_encoder_platform_data is declared in -include/linux/rotary-encoder.h and needs to be filled with the number of -steps the encoder has and can carry information about externally inverted -signals (because of an inverting buffer or other reasons). The encoder -can be set up to deliver input information as either an absolute or relative -axes. For relative axes the input event returns +/-1 for each step. For -absolute axes the position of the encoder can either roll over between zero -and the number of steps or will clamp at the maximum and zero depending on -the configuration. - -Because GPIO to IRQ mapping is platform specific, this information must -be given in separately to the driver. See the example below. - ----------<snip>--------- - -/* board support file example */ - -#include <linux/input.h> -#include <linux/rotary_encoder.h> - -#define GPIO_ROTARY_A 1 -#define GPIO_ROTARY_B 2 - -static struct rotary_encoder_platform_data my_rotary_encoder_info = { - .steps = 24, - .axis = ABS_X, - .relative_axis = false, - .rollover = false, - .gpio_a = GPIO_ROTARY_A, - .gpio_b = GPIO_ROTARY_B, - .inverted_a = 0, - .inverted_b = 0, - .half_period = false, - .wakeup_source = false, -}; - -static struct platform_device rotary_encoder_device = { - .name = "rotary-encoder", - .id = 0, - .dev = { - .platform_data = &my_rotary_encoder_info, - } -}; - |