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author | Linus Torvalds <torvalds@linux-foundation.org> | 2009-04-13 11:37:23 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2009-04-13 11:37:23 -0700 |
commit | b534d388c268ad051c72b187106a3c99021be006 (patch) | |
tree | ccfe40792b52366ce237c2043256d28916a0122e /Documentation | |
parent | c751085943362143f84346d274e0011419c84202 (diff) | |
parent | ba28f22e7cf16cb310bb491cbb3f7d0d5d1f5c5d (diff) | |
download | linux-b534d388c268ad051c72b187106a3c99021be006.tar.bz2 |
Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input: (22 commits)
Input: i8042 - add HP DV9700 to the noloop list
Input: arrange drivers/input/misc/Makefile in alphabetical order
Input: add AD7879 Touchscreen driver
Input: add AD7877 touchscreen driver
Input: bf54x-keys - fix typo in warning
Input: add driver for S1 button of rb532
Input: generic driver for rotary encoders on GPIOs
Input: hilkbd - fix crash when removing hilkbd module
Input: atkbd - add quirk for Fujitsu Siemens Amilo PA 1510
Input: atkbd - consolidate force release quirk setup
Input: add accelerated touchscreen support for Marvell Zylonite
Input: ucb1400_ts, mainstone-wm97xx - add BTN_TOUCH events
Input: wm97xx - use disable_irq_nosync() for Mainstone
Input: wm97xx - add BTN_TOUCH event to wm97xx to use it with Android
Input: fix polling of /proc/bus/input/devices
Input: psmouse - add newline to OLPC HGPK touchpad debugging
Input: ati_remote2 - check module params
Input: ati_remote2 - add per device attrs
Input: ati_remote2 - complete suspend support
Input: stop autorepeat timer on key release
...
Diffstat (limited to 'Documentation')
-rw-r--r-- | Documentation/input/rotary-encoder.txt | 101 |
1 files changed, 101 insertions, 0 deletions
diff --git a/Documentation/input/rotary-encoder.txt b/Documentation/input/rotary-encoder.txt new file mode 100644 index 000000000000..435102a26d96 --- /dev/null +++ b/Documentation/input/rotary-encoder.txt @@ -0,0 +1,101 @@ +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. + +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 + + +For more information, please see + http://en.wikipedia.org/wiki/Rotary_encoder + + +1. Events / state machine +------------------------- + +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 happend, 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 used invertig buffer or other reasons). + +Because GPIO to IRQ mapping is platform specific, this information must +be given in seperately 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, + .gpio_a = GPIO_ROTARY_A, + .gpio_b = GPIO_ROTARY_B, + .inverted_a = 0, + .inverted_b = 0, +}; + +static struct platform_device rotary_encoder_device = { + .name = "rotary-encoder", + .id = 0, + .dev = { + .platform_data = &my_rotary_encoder_info, + } +}; + |