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+/* Copyright 2023 Leorize <[email protected]>
+ * Copyright 2011 Ben Buxton <[email protected]>
+ *
+ * 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 3 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 <stdbool.h>
+#include <stdint.h>
+
+/* An extremely simple implementation of the encoder:
+ *
+ * For read out, the mechanism mimics that of a Schmitt trigger, with
+ * statically defined high/low thresholds used instead of computing
+ * one at runtime.
+ *
+ * The advantage of this approach is computing less in the decoder
+ * implementation and allow the state to be measured before the wheel
+ * moved.
+ *
+ * Compared to opt_encoder_simple.c, the use of an intermediary state
+ * reduces sensitivity and de-sensitize against tiny movements caused
+ * when lifting finger off the wheel.
+ *
+ * For turning decoded values into rotation, an algorithm inspired by
+ * http://www.buxtronix.net/2011/10/rotary-encoders-done-properly.html
+ * is employed.
+ */
+
+#if !defined(ENCODER_LOW_THRES_A) || !defined(ENCODER_HIGH_THRES_A)
+# error "The thresholds for phototransistors A is not defined in config.h"
+#endif
+#if !defined(ENCODER_LOW_THRES_B) || !defined(ENCODER_HIGH_THRES_B)
+# error "The thresholds for phototransistors B is not defined in config.h"
+#endif
+/*
+ * Sample values, captured for a Ploopy Mini Trackball
+ *
+ * The following min-max values was captured by aggregating data recorded
+ * when debug_encoder is enabled:
+ *
+ * A: min: 0, max: 214
+ * B: min: 0, max: 204
+ *
+ * The threshold specified is then defined at the 1/4 and the 3/4 points.
+ *
+ * As these values might vary between units, you're encouraged to
+ * measure your own.
+ */
+#if 0
+# define ENCODER_LOW_THRES_A 53
+# define ENCODER_HIGH_THRES_A 161
+# define ENCODER_LOW_THRES_B 52
+# define ENCODER_HIGH_THRES_B 153
+#endif
+
+/* 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)
+
+typedef enum {
+ START,
+ DOWN_BEGIN,
+ UP_BEGIN,
+ START_MID,
+ DOWN_BEGIN_MID,
+ UP_BEGIN_MID,
+ STATE_MASK = 0xf, /* 0b1111 */
+ EMIT_UP = 0x10,
+ EMIT_UP_MID = EMIT_UP & START_MID,
+ EMIT_DOWN = 0x80,
+ EMIT_DOWN_MID = EMIT_DOWN & START_MID,
+ EMIT_MASK = 0xf0
+} encoder_state_t;
+
+static encoder_state_t state;
+static uint8_t encState;
+
+static const uint8_t transitions[] = {
+ // clang-format off
+ // START -> 00, 01, 10, 11
+ START, DOWN_BEGIN, UP_BEGIN, START_MID,
+ // DOWN_BEGIN -> 00, 01, 10, 11
+ START, DOWN_BEGIN, START, EMIT_DOWN_MID,
+ // UP_BEGIN -> 00, 01, 10, 11
+ START, START, UP_BEGIN, EMIT_UP_MID,
+ // START_MID -> 00, 01, 10, 11
+ START, UP_BEGIN_MID, DOWN_BEGIN_MID, START_MID,
+ // DOWN_BEGIN_MID -> 00, 01, 10, 11
+ EMIT_DOWN, START_MID, DOWN_BEGIN_MID, START_MID,
+ // UP_BEGIN_MID -> 00, 01, 10, 11
+ EMIT_UP, UP_BEGIN_MID, START_MID, START_MID,
+ // clang-format on
+};
+
+void opt_encoder_init(void) {
+ state = START;
+ encState = 0;
+}
+
+int8_t opt_encoder_handler(uint16_t encA, uint16_t encB) {
+ encState = MAKE_STATE((STATE_A(encState) & (encA > ENCODER_LOW_THRES_A)) | (encA > ENCODER_HIGH_THRES_A), (STATE_B(encState) & (encB > ENCODER_LOW_THRES_B)) | (encB > ENCODER_HIGH_THRES_B));
+ state = transitions[((state & STATE_MASK) << 2) + encState];
+ return state & EMIT_MASK;
+}