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authorDaniel Mack <daniel@caiaq.de>2009-03-04 23:27:14 -0800
committerDmitry Torokhov <dmitry.torokhov@gmail.com>2009-03-08 16:35:53 -0700
commit73969ff0eda233f140bcbed1251431387b43f383 (patch)
treeb7dd2b670d9e03916b04469e9d38b71d69c6cd60 /Documentation/input
parentb0ecc7309443dbcf1a0ce2d93f39f5d92c124d42 (diff)
Input: generic driver for rotary encoders on GPIOs
This patch adds a generic driver for rotary encoders connected to GPIO pins of a system. It relies on gpiolib and generic hardware irqs. The documentation that also comes with this patch explains the concept and how to use the driver. Signed-off-by: Daniel Mack <daniel@caiaq.de> Tested-by: H Hartley Sweeten <hsweeten@visionengravers.com> Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
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+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,
+ }
+};
+