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73969ff0 DM |
1 | rotary-encoder - a generic driver for GPIO connected devices |
2 | Daniel Mack <daniel@caiaq.de>, Feb 2009 | |
3 | ||
4 | 0. Function | |
5 | ----------- | |
6 | ||
7 | Rotary encoders are devices which are connected to the CPU or other | |
8 | peripherals with two wires. The outputs are phase-shifted by 90 degrees | |
9 | and by triggering on falling and rising edges, the turn direction can | |
10 | be determined. | |
11 | ||
12 | The phase diagram of these two outputs look like this: | |
13 | ||
14 | _____ _____ _____ | |
15 | | | | | | | | |
16 | Channel A ____| |_____| |_____| |____ | |
17 | ||
18 | : : : : : : : : : : : : | |
19 | __ _____ _____ _____ | |
20 | | | | | | | | | |
21 | Channel B |_____| |_____| |_____| |__ | |
22 | ||
23 | : : : : : : : : : : : : | |
24 | Event a b c d a b c d a b c d | |
25 | ||
26 | |<-------->| | |
27 | one step | |
28 | ||
29 | ||
30 | For more information, please see | |
31 | http://en.wikipedia.org/wiki/Rotary_encoder | |
32 | ||
33 | ||
34 | 1. Events / state machine | |
35 | ------------------------- | |
36 | ||
37 | a) Rising edge on channel A, channel B in low state | |
38 | This state is used to recognize a clockwise turn | |
39 | ||
40 | b) Rising edge on channel B, channel A in high state | |
41 | When entering this state, the encoder is put into 'armed' state, | |
42 | meaning that there it has seen half the way of a one-step transition. | |
43 | ||
44 | c) Falling edge on channel A, channel B in high state | |
45 | This state is used to recognize a counter-clockwise turn | |
46 | ||
47 | d) Falling edge on channel B, channel A in low state | |
48 | Parking position. If the encoder enters this state, a full transition | |
49 | should have happend, unless it flipped back on half the way. The | |
50 | 'armed' state tells us about that. | |
51 | ||
52 | 2. Platform requirements | |
53 | ------------------------ | |
54 | ||
55 | As there is no hardware dependent call in this driver, the platform it is | |
56 | used with must support gpiolib. Another requirement is that IRQs must be | |
57 | able to fire on both edges. | |
58 | ||
59 | ||
60 | 3. Board integration | |
61 | -------------------- | |
62 | ||
63 | To use this driver in your system, register a platform_device with the | |
64 | name 'rotary-encoder' and associate the IRQs and some specific platform | |
65 | data with it. | |
66 | ||
67 | struct rotary_encoder_platform_data is declared in | |
68 | include/linux/rotary-encoder.h and needs to be filled with the number of | |
69 | steps the encoder has and can carry information about externally inverted | |
bd3ce655 HS |
70 | signals (because of an inverting buffer or other reasons). The encoder |
71 | can be set up to deliver input information as either an absolute or relative | |
72 | axes. For relative axes the input event returns +/-1 for each step. For | |
73 | absolute axes the position of the encoder can either roll over between zero | |
74 | and the number of steps or will clamp at the maximum and zero depending on | |
75 | the configuration. | |
73969ff0 DM |
76 | |
77 | Because GPIO to IRQ mapping is platform specific, this information must | |
3ad2f3fb | 78 | be given in separately to the driver. See the example below. |
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79 | |
80 | ---------<snip>--------- | |
81 | ||
82 | /* board support file example */ | |
83 | ||
84 | #include <linux/input.h> | |
85 | #include <linux/rotary_encoder.h> | |
86 | ||
87 | #define GPIO_ROTARY_A 1 | |
88 | #define GPIO_ROTARY_B 2 | |
89 | ||
90 | static struct rotary_encoder_platform_data my_rotary_encoder_info = { | |
91 | .steps = 24, | |
92 | .axis = ABS_X, | |
bd3ce655 HS |
93 | .relative_axis = false, |
94 | .rollover = false, | |
73969ff0 DM |
95 | .gpio_a = GPIO_ROTARY_A, |
96 | .gpio_b = GPIO_ROTARY_B, | |
97 | .inverted_a = 0, | |
98 | .inverted_b = 0, | |
99 | }; | |
100 | ||
101 | static struct platform_device rotary_encoder_device = { | |
102 | .name = "rotary-encoder", | |
103 | .id = 0, | |
104 | .dev = { | |
105 | .platform_data = &my_rotary_encoder_info, | |
106 | } | |
107 | }; | |
108 |