RFC: add a simple implementation of the ploopy optical encoder (#17912)

1 files changed, 147 insertions, 0 deletions

diff --git a/keyboards/ploopyco/opt_encoder_simple.c b/keyboards/ploopyco/opt_encoder_simple.c
new file mode 100644
index 0000000000..c30deb9ca4
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+++ b/keyboards/ploopyco/opt_encoder_simple.c
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+/* Copyright 2020 Christopher Courtney, aka Drashna Jael're  (@drashna) <drashna@live.com>
+ * Copyright 2020 Ploopy Corporation
+ * Copyright 2022 Leorize <leorize+oss@disroot.org>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#include "opt_encoder.h"
+#include "util.h"
+#include <stdbool.h>
+#include <stdint.h>
+
+/* An alternative implementation for interpreting the encoder status:
+ *
+ * From graphing the phototransistor voltages, the peak and baseline appears to
+ * be rather stable. Therefore there is no need to average them out, and instead
+ * just simply store the min and max voltages of each phototransistor.
+ *
+ * This algorithm then distinguish between high and low states by employing an
+ * approach similar to a Schmitt trigger: a low and high threshold is defined
+ * for each phototransistor based on their min and max voltages.
+ *
+ * Currently, the thresholds are:
+ *
+ * * High threshold: The upper quarter of the voltage range.
+ * * Low threshold: The lower quarter of the voltage range.
+ *
+ * these thresholds are defined for each phototransistor.
+ *
+ * For a state to cross from high -> low, it must fall below the low threshold.
+ * Similarly, to cross from low -> high, the voltage must be higher than the
+ * high threshold.
+ *
+ * Having two distinct thresholds filters out the bulk of noise from the
+ * phototransistors.
+ *
+ * For converting the resulting high and low signals into rotation, a simple
+ * quadrature decoder is used.
+ */
+
+/* The minimum value returned by the ADC */
+#define ENCODER_MIN 0
+/* The maximum value returned by the ADC */
+#define ENCODER_MAX 1023
+
+/* Utilities for composing the encoder state */
+#define MAKE_STATE(HI_A, HI_B) (((uint8_t)((HI_A) & 0x1) << 1) | ((uint8_t)((HI_B) & 0x1)))
+#define STATE_A(st) ((st & 0x2) >> 1)
+#define STATE_B(st) (st & 0x1)
+#define LOLO MAKE_STATE(0, 0)
+#define HILO MAKE_STATE(1, 0)
+#define LOHI MAKE_STATE(0, 1)
+
+typedef enum {
+    CALIBRATION, /* Recalibrate encoder state by waiting for a 01 -> 00 or 10 -> 00 transistion */
+    DECODE /* Translate changes in the encoder state into movement */
+} encoder_state_t;
+
+static encoder_state_t mode;
+
+static uint8_t lastState;
+
+static uint16_t lowA;
+static uint16_t highA;
+static uint16_t lowB;
+static uint16_t highB;
+
+#define MOVE_UP 1
+#define MOVE_DOWN -1
+#define MOVE_NONE 0
+#define MOVE_ERR 0x7F
+static const uint8_t movement[] = {
+    // 00 -> 00, 01, 10, 11
+    MOVE_NONE, MOVE_DOWN, MOVE_UP, MOVE_ERR,
+    // 01 -> 00, 01, 10, 11
+    MOVE_UP, MOVE_NONE, MOVE_ERR, MOVE_DOWN,
+    // 10 -> 00, 01, 10, 11
+    MOVE_DOWN, MOVE_ERR, MOVE_NONE, MOVE_UP,
+    // 11 -> 00, 01, 10, 11
+    MOVE_ERR, MOVE_UP, MOVE_DOWN, MOVE_NONE
+};
+
+void opt_encoder_init(void) {
+    mode = CALIBRATION;
+    lastState = 0;
+
+    lowA = ENCODER_MAX;
+    lowB = ENCODER_MAX;
+    highA = ENCODER_MIN;
+    highB = ENCODER_MIN;
+}
+
+int8_t opt_encoder_handler(uint16_t encA, uint16_t encB) {
+    int8_t result = 0;
+
+    highA = MAX(encA, highA);
+    lowA = MIN(encA, lowA);
+    highB = MAX(encB, highB);
+    lowB = MIN(encB, lowB);
+
+    /* Only compute the thresholds after a large enough range is established */
+    if (highA - lowA > SCROLL_THRESH_RANGE_LIM && highB - lowB > SCROLL_THRESH_RANGE_LIM) {
+        const int16_t lowThresholdA = (highA + lowA) / 4;
+        const int16_t highThresholdA = (highA + lowA) - lowThresholdA;
+        const int16_t lowThresholdB = (highB + lowB) / 4;
+        const int16_t highThresholdB = (highB + lowB) - lowThresholdB;
+
+        uint8_t state = MAKE_STATE(
+            STATE_A(lastState) ? encA > lowThresholdA : encA > highThresholdA,
+            STATE_B(lastState) ? encB > lowThresholdB : encB > highThresholdB
+        );
+
+        switch (mode) {
+            case CALIBRATION:
+                if ((lastState == HILO && state == LOLO)
+                        || (lastState == LOHI && state == LOLO))
+                    mode = DECODE;
+                else
+                    mode = CALIBRATION;
+                break;
+
+            case DECODE:
+                result = movement[lastState * 4 + state];
+                /* If we detect a state change that should not be possible,
+                 * then the wheel might have moved too fast and we need to
+                 * recalibrate the encoder position. */
+                mode = result == MOVE_ERR ? CALIBRATION : mode;
+                result = result == MOVE_ERR ? MOVE_NONE : result;
+
+                break;
+        }
+
+        lastState = state;
+    }
+
+    return result;
+}