136 lines · plain
1============================================================2rotary-encoder - a generic driver for GPIO connected devices3============================================================4 5:Author: Daniel Mack <daniel@caiaq.de>, Feb 20096 7Function8--------9 10Rotary encoders are devices which are connected to the CPU or other11peripherals with two wires. The outputs are phase-shifted by 90 degrees12and by triggering on falling and rising edges, the turn direction can13be determined.14 15Some encoders have both outputs low in stable states, others also have16a stable state with both outputs high (half-period mode) and some have17a stable state in all steps (quarter-period mode).18 19The phase diagram of these two outputs look like this::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 d32 33 |<-------->|34 one step35 36 |<-->|37 one step (half-period mode)38 39 |<>|40 one step (quarter-period mode)41 42For more information, please see43 https://en.wikipedia.org/wiki/Rotary_encoder44 45 46Events / state machine47----------------------48 49In half-period mode, state a) and c) above are used to determine the50rotational direction based on the last stable state. Events are reported in51states b) and d) given that the new stable state is different from the last52(i.e. the rotation was not reversed half-way).53 54Otherwise, the following apply:55 56a) Rising edge on channel A, channel B in low state57 This state is used to recognize a clockwise turn58 59b) Rising edge on channel B, channel A in high state60 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 63c) Falling edge on channel A, channel B in high state64 This state is used to recognize a counter-clockwise turn65 66d) Falling edge on channel B, channel A in low state67 Parking position. If the encoder enters this state, a full transition68 should have happened, unless it flipped back on half the way. The69 'armed' state tells us about that.70 71Platform requirements72---------------------73 74As there is no hardware dependent call in this driver, the platform it is75used with must support gpiolib. Another requirement is that IRQs must be76able to fire on both edges.77 78 79Board integration80-----------------81 82To use this driver in your system, register a platform_device with the83name 'rotary-encoder' and associate the IRQs and some specific platform84data with it. Because the driver uses generic device properties, this can85be done either via device tree, ACPI, or using static board files, like in86example below:87 88::89 90 /* board support file example */91 92 #include <linux/input.h>93 #include <linux/gpio/machine.h>94 #include <linux/property.h>95 96 #define GPIO_ROTARY_A 197 #define GPIO_ROTARY_B 298 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[] = {111 PROPERTY_ENTRY_U32("rotary-encoder,steps-per-period", 24),112 PROPERTY_ENTRY_U32("linux,axis", ABS_X),113 PROPERTY_ENTRY_U32("rotary-encoder,relative_axis", 0),114 { },115 };116 117 static const struct software_node rotary_encoder_node = {118 .properties = rotary_encoder_properties,119 };120 121 static struct platform_device rotary_encoder_device = {122 .name = "rotary-encoder",123 .id = 0,124 };125 126 ...127 128 gpiod_add_lookup_table(&rotary_encoder_gpios);129 device_add_software_node(&rotary_encoder_device.dev, &rotary_encoder_node);130 platform_device_register(&rotary_encoder_device);131 132 ...133 134Please consult device tree binding documentation to see all properties135supported by the driver.136