142 lines
4.9 KiB
C
142 lines
4.9 KiB
C
/* Copyright 2020 Christopher Courtney, aka Drashna Jael're (@drashna) <drashna@live.com>
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* Copyright 2020 Ploopy Corporation
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* Copyright 2022 Leorize <leorize+oss@disroot.org>
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include "opt_encoder.h"
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#include "util.h"
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#include <stdbool.h>
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#include <stdint.h>
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/* An alternative implementation for interpreting the encoder status:
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*
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* From graphing the phototransistor voltages, the peak and baseline appears to
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* be rather stable. Therefore there is no need to average them out, and instead
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* just simply store the min and max voltages of each phototransistor.
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*
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* This algorithm then distinguish between high and low states by employing an
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* approach similar to a Schmitt trigger: a low and high threshold is defined
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* for each phototransistor based on their min and max voltages.
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*
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* Currently, the thresholds are:
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*
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* * High threshold: The upper quarter of the voltage range.
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* * Low threshold: The lower quarter of the voltage range.
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*
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* these thresholds are defined for each phototransistor.
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*
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* For a state to cross from high -> low, it must fall below the low threshold.
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* Similarly, to cross from low -> high, the voltage must be higher than the
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* high threshold.
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*
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* Having two distinct thresholds filters out the bulk of noise from the
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* phototransistors.
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*
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* For converting the resulting high and low signals into rotation, a simple
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* quadrature decoder is used.
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*/
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/* The minimum value returned by the ADC */
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#define ENCODER_MIN 0
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/* The maximum value returned by the ADC */
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#define ENCODER_MAX 1023
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/* Utilities for composing the encoder state */
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#define MAKE_STATE(HI_A, HI_B) (((uint8_t)((HI_A) & 0x1) << 1) | ((uint8_t)((HI_B) & 0x1)))
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#define STATE_A(st) ((st & 0x2) >> 1)
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#define STATE_B(st) (st & 0x1)
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#define LOLO MAKE_STATE(0, 0)
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#define HILO MAKE_STATE(1, 0)
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#define LOHI MAKE_STATE(0, 1)
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typedef enum {
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CALIBRATION, /* Recalibrate encoder state by waiting for a 01 -> 00 or 10 -> 00 transistion */
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DECODE /* Translate changes in the encoder state into movement */
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} encoder_state_t;
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static encoder_state_t mode;
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static uint8_t lastState;
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static uint16_t lowA;
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static uint16_t highA;
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static uint16_t lowB;
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static uint16_t highB;
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#define MOVE_UP 1
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#define MOVE_DOWN -1
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#define MOVE_NONE 0
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#define MOVE_ERR 0x7F
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static const uint8_t movement[] = {
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// 00 -> 00, 01, 10, 11
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MOVE_NONE, MOVE_DOWN, MOVE_UP, MOVE_ERR,
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// 01 -> 00, 01, 10, 11
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MOVE_UP, MOVE_NONE, MOVE_ERR, MOVE_DOWN,
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// 10 -> 00, 01, 10, 11
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MOVE_DOWN, MOVE_ERR, MOVE_NONE, MOVE_UP,
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// 11 -> 00, 01, 10, 11
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MOVE_ERR, MOVE_UP, MOVE_DOWN, MOVE_NONE};
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void opt_encoder_init(void) {
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mode = CALIBRATION;
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lastState = 0;
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lowA = ENCODER_MAX;
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lowB = ENCODER_MAX;
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highA = ENCODER_MIN;
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highB = ENCODER_MIN;
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}
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int8_t opt_encoder_handler(uint16_t encA, uint16_t encB) {
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int8_t result = 0;
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highA = MAX(encA, highA);
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lowA = MIN(encA, lowA);
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highB = MAX(encB, highB);
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lowB = MIN(encB, lowB);
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/* Only compute the thresholds after a large enough range is established */
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if (highA - lowA > SCROLL_THRESH_RANGE_LIM && highB - lowB > SCROLL_THRESH_RANGE_LIM) {
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const int16_t lowThresholdA = (highA + lowA) / 4;
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const int16_t highThresholdA = (highA + lowA) - lowThresholdA;
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const int16_t lowThresholdB = (highB + lowB) / 4;
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const int16_t highThresholdB = (highB + lowB) - lowThresholdB;
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uint8_t state = MAKE_STATE(STATE_A(lastState) ? encA > lowThresholdA : encA > highThresholdA, STATE_B(lastState) ? encB > lowThresholdB : encB > highThresholdB);
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switch (mode) {
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case CALIBRATION:
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if ((lastState == HILO && state == LOLO) || (lastState == LOHI && state == LOLO))
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mode = DECODE;
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else
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mode = CALIBRATION;
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break;
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case DECODE:
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result = movement[lastState * 4 + state];
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/* If we detect a state change that should not be possible,
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* then the wheel might have moved too fast and we need to
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* recalibrate the encoder position. */
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mode = result == MOVE_ERR ? CALIBRATION : mode;
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result = result == MOVE_ERR ? MOVE_NONE : result;
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break;
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}
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lastState = state;
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}
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return result;
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}
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