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42f2309b | 1 | ============================================================ |
73969ff0 | 2 | rotary-encoder - a generic driver for GPIO connected devices |
42f2309b | 3 | ============================================================ |
73969ff0 | 4 | |
42f2309b MCC |
5 | :Author: Daniel Mack <daniel@caiaq.de>, Feb 2009 |
6 | ||
7 | Function | |
8 | -------- | |
73969ff0 DM |
9 | |
10 | Rotary encoders are devices which are connected to the CPU or other | |
11 | peripherals with two wires. The outputs are phase-shifted by 90 degrees | |
12 | and by triggering on falling and rising edges, the turn direction can | |
13 | be determined. | |
14 | ||
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15 | Some encoders have both outputs low in stable states, others also have |
16 | a stable state with both outputs high (half-period mode) and some have | |
17 | a stable state in all steps (quarter-period mode). | |
e70bdd41 | 18 | |
42f2309b | 19 | The phase diagram of these two outputs look like this:: |
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20 | |
21 | _____ _____ _____ | |
22 | | | | | | | | |
23 | Channel A ____| |_____| |_____| |____ | |
24 | ||
25 | : : : : : : : : : : : : | |
26 | __ _____ _____ _____ | |
27 | | | | | | | | | |
28 | Channel B |_____| |_____| |_____| |__ | |
29 | ||
30 | : : : : : : : : : : : : | |
31 | Event a b c d a b c d a b c d | |
32 | ||
33 | |<-------->| | |
34 | one step | |
35 | ||
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36 | |<-->| |
37 | one step (half-period mode) | |
73969ff0 | 38 | |
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39 | |<>| |
40 | one step (quarter-period mode) | |
41 | ||
73969ff0 | 42 | For more information, please see |
ae13c65b | 43 | https://en.wikipedia.org/wiki/Rotary_encoder |
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44 | |
45 | ||
42f2309b MCC |
46 | Events / state machine |
47 | ---------------------- | |
73969ff0 | 48 | |
e70bdd41 JH |
49 | In half-period mode, state a) and c) above are used to determine the |
50 | rotational direction based on the last stable state. Events are reported in | |
51 | states b) and d) given that the new stable state is different from the last | |
52 | (i.e. the rotation was not reversed half-way). | |
53 | ||
54 | Otherwise, the following apply: | |
55 | ||
73969ff0 DM |
56 | a) Rising edge on channel A, channel B in low state |
57 | This state is used to recognize a clockwise turn | |
58 | ||
59 | b) Rising edge on channel B, channel A in high state | |
60 | When entering this state, the encoder is put into 'armed' state, | |
61 | meaning that there it has seen half the way of a one-step transition. | |
62 | ||
63 | c) Falling edge on channel A, channel B in high state | |
64 | This state is used to recognize a counter-clockwise turn | |
65 | ||
66 | d) Falling edge on channel B, channel A in low state | |
67 | Parking position. If the encoder enters this state, a full transition | |
25985edc | 68 | should have happened, unless it flipped back on half the way. The |
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69 | 'armed' state tells us about that. |
70 | ||
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71 | Platform requirements |
72 | --------------------- | |
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73 | |
74 | As there is no hardware dependent call in this driver, the platform it is | |
75 | used with must support gpiolib. Another requirement is that IRQs must be | |
76 | able to fire on both edges. | |
77 | ||
78 | ||
42f2309b MCC |
79 | Board integration |
80 | ----------------- | |
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81 | |
82 | To use this driver in your system, register a platform_device with the | |
83 | name 'rotary-encoder' and associate the IRQs and some specific platform | |
01ef6601 DT |
84 | data with it. Because the driver uses generic device properties, this can |
85 | be done either via device tree, ACPI, or using static board files, like in | |
86 | example below: | |
73969ff0 | 87 | |
01ef6601 | 88 | :: |
73969ff0 | 89 | |
01ef6601 | 90 | /* board support file example */ |
73969ff0 | 91 | |
01ef6601 DT |
92 | #include <linux/input.h> |
93 | #include <linux/gpio/machine.h> | |
94 | #include <linux/property.h> | |
95 | ||
96 | #define GPIO_ROTARY_A 1 | |
97 | #define GPIO_ROTARY_B 2 | |
98 | ||
99 | static struct gpiod_lookup_table rotary_encoder_gpios = { | |
100 | .dev_id = "rotary-encoder.0", | |
101 | .table = { | |
102 | GPIO_LOOKUP_IDX("gpio-0", | |
103 | GPIO_ROTARY_A, NULL, 0, GPIO_ACTIVE_LOW), | |
104 | GPIO_LOOKUP_IDX("gpio-0", | |
105 | GPIO_ROTARY_B, NULL, 1, GPIO_ACTIVE_HIGH), | |
106 | { }, | |
107 | }, | |
108 | }; | |
109 | ||
110 | static const struct property_entry rotary_encoder_properties[] __initconst = { | |
111 | PROPERTY_ENTRY_INTEGER("rotary-encoder,steps-per-period", u32, 24), | |
112 | PROPERTY_ENTRY_INTEGER("linux,axis", u32, ABS_X), | |
113 | PROPERTY_ENTRY_INTEGER("rotary-encoder,relative_axis", u32, 0), | |
114 | { }, | |
115 | }; | |
116 | ||
117 | static struct platform_device rotary_encoder_device = { | |
118 | .name = "rotary-encoder", | |
119 | .id = 0, | |
120 | }; | |
121 | ||
122 | ... | |
123 | ||
124 | gpiod_add_lookup_table(&rotary_encoder_gpios); | |
125 | device_add_properties(&rotary_encoder_device, rotary_encoder_properties); | |
126 | platform_device_register(&rotary_encoder_device); | |
127 | ||
128 | ... | |
42f2309b | 129 | |
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130 | Please consult device tree binding documentation to see all properties |
131 | supported by the driver. |