1 ============================================== 1 ============================================================
2 rotary-encoder - a generic driver for GPIO con 2 rotary-encoder - a generic driver for GPIO connected devices
3 ============================================== 3 ============================================================
4 4
5 :Author: Daniel Mack <daniel@caiaq.de>, Feb 200 5 :Author: Daniel Mack <daniel@caiaq.de>, Feb 2009
6 6
7 Function 7 Function
8 -------- 8 --------
9 9
10 Rotary encoders are devices which are connecte 10 Rotary encoders are devices which are connected to the CPU or other
11 peripherals with two wires. The outputs are ph 11 peripherals with two wires. The outputs are phase-shifted by 90 degrees
12 and by triggering on falling and rising edges, 12 and by triggering on falling and rising edges, the turn direction can
13 be determined. 13 be determined.
14 14
15 Some encoders have both outputs low in stable 15 Some encoders have both outputs low in stable states, others also have
16 a stable state with both outputs high (half-pe 16 a stable state with both outputs high (half-period mode) and some have
17 a stable state in all steps (quarter-period mo 17 a stable state in all steps (quarter-period mode).
18 18
19 The phase diagram of these two outputs look li 19 The phase diagram of these two outputs look like this::
20 20
21 _____ _____ ____ 21 _____ _____ _____
22 | | | | | 22 | | | | | |
23 Channel A ____| |_____| |_____| 23 Channel A ____| |_____| |_____| |____
24 24
25 : : : : : : : : : : 25 : : : : : : : : : : : :
26 __ _____ _____ _ 26 __ _____ _____ _____
27 | | | | | | 27 | | | | | | |
28 Channel B |_____| |_____| |_____| 28 Channel B |_____| |_____| |_____| |__
29 29
30 : : : : : : : : : : 30 : : : : : : : : : : : :
31 Event a b c d a b c d a b 31 Event a b c d a b c d a b c d
32 32
33 |<-------->| 33 |<-------->|
34 one step 34 one step
35 35
36 |<-->| 36 |<-->|
37 one step (half-period mode) 37 one step (half-period mode)
38 38
39 |<>| 39 |<>|
40 one step (quarter-period mod 40 one step (quarter-period mode)
41 41
42 For more information, please see 42 For more information, please see
43 https://en.wikipedia.org/wiki/Rotary_e 43 https://en.wikipedia.org/wiki/Rotary_encoder
44 44
45 45
46 Events / state machine 46 Events / state machine
47 ---------------------- 47 ----------------------
48 48
49 In half-period mode, state a) and c) above are 49 In half-period mode, state a) and c) above are used to determine the
50 rotational direction based on the last stable 50 rotational direction based on the last stable state. Events are reported in
51 states b) and d) given that the new stable sta 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). 52 (i.e. the rotation was not reversed half-way).
53 53
54 Otherwise, the following apply: 54 Otherwise, the following apply:
55 55
56 a) Rising edge on channel A, channel B in low 56 a) Rising edge on channel A, channel B in low state
57 This state is used to recognize a cloc 57 This state is used to recognize a clockwise turn
58 58
59 b) Rising edge on channel B, channel A in high 59 b) Rising edge on channel B, channel A in high state
60 When entering this state, the encoder 60 When entering this state, the encoder is put into 'armed' state,
61 meaning that there it has seen half th 61 meaning that there it has seen half the way of a one-step transition.
62 62
63 c) Falling edge on channel A, channel B in hig 63 c) Falling edge on channel A, channel B in high state
64 This state is used to recognize a coun 64 This state is used to recognize a counter-clockwise turn
65 65
66 d) Falling edge on channel B, channel A in low 66 d) Falling edge on channel B, channel A in low state
67 Parking position. If the encoder enter 67 Parking position. If the encoder enters this state, a full transition
68 should have happened, unless it flippe 68 should have happened, unless it flipped back on half the way. The
69 'armed' state tells us about that. 69 'armed' state tells us about that.
70 70
71 Platform requirements 71 Platform requirements
72 --------------------- 72 ---------------------
73 73
74 As there is no hardware dependent call in this 74 As there is no hardware dependent call in this driver, the platform it is
75 used with must support gpiolib. Another requir 75 used with must support gpiolib. Another requirement is that IRQs must be
76 able to fire on both edges. 76 able to fire on both edges.
77 77
78 78
79 Board integration 79 Board integration
80 ----------------- 80 -----------------
81 81
82 To use this driver in your system, register a 82 To use this driver in your system, register a platform_device with the
83 name 'rotary-encoder' and associate the IRQs a 83 name 'rotary-encoder' and associate the IRQs and some specific platform
84 data with it. Because the driver uses generic 84 data with it. Because the driver uses generic device properties, this can
85 be done either via device tree, ACPI, or using 85 be done either via device tree, ACPI, or using static board files, like in
86 example below: 86 example below:
87 87
88 :: 88 ::
89 89
90 /* board support file example */ 90 /* board support file example */
91 91
92 #include <linux/input.h> 92 #include <linux/input.h>
93 #include <linux/gpio/machine.h> 93 #include <linux/gpio/machine.h>
94 #include <linux/property.h> 94 #include <linux/property.h>
95 95
96 #define GPIO_ROTARY_A 1 96 #define GPIO_ROTARY_A 1
97 #define GPIO_ROTARY_B 2 97 #define GPIO_ROTARY_B 2
98 98
99 static struct gpiod_lookup_table rotar 99 static struct gpiod_lookup_table rotary_encoder_gpios = {
100 .dev_id = "rotary-encoder.0", 100 .dev_id = "rotary-encoder.0",
101 .table = { 101 .table = {
102 GPIO_LOOKUP_IDX("gpio- 102 GPIO_LOOKUP_IDX("gpio-0",
103 GPIO_R 103 GPIO_ROTARY_A, NULL, 0, GPIO_ACTIVE_LOW),
104 GPIO_LOOKUP_IDX("gpio- 104 GPIO_LOOKUP_IDX("gpio-0",
105 GPIO_R 105 GPIO_ROTARY_B, NULL, 1, GPIO_ACTIVE_HIGH),
106 { }, 106 { },
107 }, 107 },
108 }; 108 };
109 109
110 static const struct property_entry rot !! 110 static const struct property_entry rotary_encoder_properties[] __initconst = {
111 PROPERTY_ENTRY_U32("rotary-enc 111 PROPERTY_ENTRY_U32("rotary-encoder,steps-per-period", 24),
112 PROPERTY_ENTRY_U32("linux,axis 112 PROPERTY_ENTRY_U32("linux,axis", ABS_X),
113 PROPERTY_ENTRY_U32("rotary-enc 113 PROPERTY_ENTRY_U32("rotary-encoder,relative_axis", 0),
114 { }, 114 { },
115 }; 115 };
116 116
117 static const struct software_node rota <<
118 .properties = rotary_encoder_p <<
119 }; <<
120 <<
121 static struct platform_device rotary_e 117 static struct platform_device rotary_encoder_device = {
122 .name = "rotary-enco 118 .name = "rotary-encoder",
123 .id = 0, 119 .id = 0,
124 }; 120 };
125 121
126 ... 122 ...
127 123
128 gpiod_add_lookup_table(&rotary_encoder 124 gpiod_add_lookup_table(&rotary_encoder_gpios);
129 device_add_software_node(&rotary_encod !! 125 device_add_properties(&rotary_encoder_device, rotary_encoder_properties);
130 platform_device_register(&rotary_encod 126 platform_device_register(&rotary_encoder_device);
131 127
132 ... 128 ...
133 129
134 Please consult device tree binding documentati 130 Please consult device tree binding documentation to see all properties
135 supported by the driver. 131 supported by the driver.
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