IoTKitV3 / QEI

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QEI.cpp@0:2c2b8af11b2d, 2018-09-20 (annotated)

Committer:
marcel1691
Date:
Thu Sep 20 17:51:37 2018 +0000
Revision:
0:2c2b8af11b2d
Quadrature Encoder Interface

Who changed what in which revision?

UserRevisionLine numberNew contents of line
marcel1691 0:2c2b8af11b2d 1 /**
marcel1691 0:2c2b8af11b2d 2 * @author Aaron Berk
marcel1691 0:2c2b8af11b2d 3 *
marcel1691 0:2c2b8af11b2d 4 * @section LICENSE
marcel1691 0:2c2b8af11b2d 5 *
marcel1691 0:2c2b8af11b2d 6 * Copyright (c) 2010 ARM Limited
marcel1691 0:2c2b8af11b2d 7 *
marcel1691 0:2c2b8af11b2d 8 * Permission is hereby granted, free of charge, to any person obtaining a copy
marcel1691 0:2c2b8af11b2d 9 * of this software and associated documentation files (the "Software"), to deal
marcel1691 0:2c2b8af11b2d 10 * in the Software without restriction, including without limitation the rights
marcel1691 0:2c2b8af11b2d 11 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
marcel1691 0:2c2b8af11b2d 12 * copies of the Software, and to permit persons to whom the Software is
marcel1691 0:2c2b8af11b2d 13 * furnished to do so, subject to the following conditions:
marcel1691 0:2c2b8af11b2d 14 *
marcel1691 0:2c2b8af11b2d 15 * The above copyright notice and this permission notice shall be included in
marcel1691 0:2c2b8af11b2d 16 * all copies or substantial portions of the Software.
marcel1691 0:2c2b8af11b2d 17 *
marcel1691 0:2c2b8af11b2d 18 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
marcel1691 0:2c2b8af11b2d 19 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
marcel1691 0:2c2b8af11b2d 20 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
marcel1691 0:2c2b8af11b2d 21 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
marcel1691 0:2c2b8af11b2d 22 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
marcel1691 0:2c2b8af11b2d 23 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
marcel1691 0:2c2b8af11b2d 24 * THE SOFTWARE.
marcel1691 0:2c2b8af11b2d 25 *
marcel1691 0:2c2b8af11b2d 26 * @section DESCRIPTION
marcel1691 0:2c2b8af11b2d 27 *
marcel1691 0:2c2b8af11b2d 28 * Quadrature Encoder Interface.
marcel1691 0:2c2b8af11b2d 29 *
marcel1691 0:2c2b8af11b2d 30 * A quadrature encoder consists of two code tracks on a disc which are 90
marcel1691 0:2c2b8af11b2d 31 * degrees out of phase. It can be used to determine how far a wheel has
marcel1691 0:2c2b8af11b2d 32 * rotated, relative to a known starting position.
marcel1691 0:2c2b8af11b2d 33 *
marcel1691 0:2c2b8af11b2d 34 * Only one code track changes at a time leading to a more robust system than
marcel1691 0:2c2b8af11b2d 35 * a single track, because any jitter around any edge won't cause a state
marcel1691 0:2c2b8af11b2d 36 * change as the other track will remain constant.
marcel1691 0:2c2b8af11b2d 37 *
marcel1691 0:2c2b8af11b2d 38 * Encoders can be a homebrew affair, consisting of infrared emitters/receivers
marcel1691 0:2c2b8af11b2d 39 * and paper code tracks consisting of alternating black and white sections;
marcel1691 0:2c2b8af11b2d 40 * alternatively, complete disk and PCB emitter/receiver encoder systems can
marcel1691 0:2c2b8af11b2d 41 * be bought, but the interface, regardless of implementation is the same.
marcel1691 0:2c2b8af11b2d 42 *
marcel1691 0:2c2b8af11b2d 43 * +-----+ +-----+ +-----+
marcel1691 0:2c2b8af11b2d 44 * Channel A | ^ | | | | |
marcel1691 0:2c2b8af11b2d 45 * ---+ ^ +-----+ +-----+ +-----
marcel1691 0:2c2b8af11b2d 46 * ^ ^
marcel1691 0:2c2b8af11b2d 47 * ^ +-----+ +-----+ +-----+
marcel1691 0:2c2b8af11b2d 48 * Channel B ^ | | | | | |
marcel1691 0:2c2b8af11b2d 49 * ------+ +-----+ +-----+ +-----
marcel1691 0:2c2b8af11b2d 50 * ^ ^
marcel1691 0:2c2b8af11b2d 51 * ^ ^
marcel1691 0:2c2b8af11b2d 52 * 90deg
marcel1691 0:2c2b8af11b2d 53 *
marcel1691 0:2c2b8af11b2d 54 * The interface uses X2 encoding by default which calculates the pulse count
marcel1691 0:2c2b8af11b2d 55 * based on reading the current state after each rising and falling edge of
marcel1691 0:2c2b8af11b2d 56 * channel A.
marcel1691 0:2c2b8af11b2d 57 *
marcel1691 0:2c2b8af11b2d 58 * +-----+ +-----+ +-----+
marcel1691 0:2c2b8af11b2d 59 * Channel A | | | | | |
marcel1691 0:2c2b8af11b2d 60 * ---+ +-----+ +-----+ +-----
marcel1691 0:2c2b8af11b2d 61 * ^ ^ ^ ^ ^
marcel1691 0:2c2b8af11b2d 62 * ^ +-----+ ^ +-----+ ^ +-----+
marcel1691 0:2c2b8af11b2d 63 * Channel B ^ | ^ | ^ | ^ | ^ | |
marcel1691 0:2c2b8af11b2d 64 * ------+ ^ +-----+ ^ +-----+ +--
marcel1691 0:2c2b8af11b2d 65 * ^ ^ ^ ^ ^
marcel1691 0:2c2b8af11b2d 66 * ^ ^ ^ ^ ^
marcel1691 0:2c2b8af11b2d 67 * Pulse count 0 1 2 3 4 5 ...
marcel1691 0:2c2b8af11b2d 68 *
marcel1691 0:2c2b8af11b2d 69 * This interface can also use X4 encoding which calculates the pulse count
marcel1691 0:2c2b8af11b2d 70 * based on reading the current state after each rising and falling edge of
marcel1691 0:2c2b8af11b2d 71 * either channel.
marcel1691 0:2c2b8af11b2d 72 *
marcel1691 0:2c2b8af11b2d 73 * +-----+ +-----+ +-----+
marcel1691 0:2c2b8af11b2d 74 * Channel A | | | | | |
marcel1691 0:2c2b8af11b2d 75 * ---+ +-----+ +-----+ +-----
marcel1691 0:2c2b8af11b2d 76 * ^ ^ ^ ^ ^
marcel1691 0:2c2b8af11b2d 77 * ^ +-----+ ^ +-----+ ^ +-----+
marcel1691 0:2c2b8af11b2d 78 * Channel B ^ | ^ | ^ | ^ | ^ | |
marcel1691 0:2c2b8af11b2d 79 * ------+ ^ +-----+ ^ +-----+ +--
marcel1691 0:2c2b8af11b2d 80 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
marcel1691 0:2c2b8af11b2d 81 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
marcel1691 0:2c2b8af11b2d 82 * Pulse count 0 1 2 3 4 5 6 7 8 9 ...
marcel1691 0:2c2b8af11b2d 83 *
marcel1691 0:2c2b8af11b2d 84 * It defaults
marcel1691 0:2c2b8af11b2d 85 *
marcel1691 0:2c2b8af11b2d 86 * An optional index channel can be used which determines when a full
marcel1691 0:2c2b8af11b2d 87 * revolution has occured.
marcel1691 0:2c2b8af11b2d 88 *
marcel1691 0:2c2b8af11b2d 89 * If a 4 pules per revolution encoder was used, with X4 encoding,
marcel1691 0:2c2b8af11b2d 90 * the following would be observed.
marcel1691 0:2c2b8af11b2d 91 *
marcel1691 0:2c2b8af11b2d 92 * +-----+ +-----+ +-----+
marcel1691 0:2c2b8af11b2d 93 * Channel A | | | | | |
marcel1691 0:2c2b8af11b2d 94 * ---+ +-----+ +-----+ +-----
marcel1691 0:2c2b8af11b2d 95 * ^ ^ ^ ^ ^
marcel1691 0:2c2b8af11b2d 96 * ^ +-----+ ^ +-----+ ^ +-----+
marcel1691 0:2c2b8af11b2d 97 * Channel B ^ | ^ | ^ | ^ | ^ | |
marcel1691 0:2c2b8af11b2d 98 * ------+ ^ +-----+ ^ +-----+ +--
marcel1691 0:2c2b8af11b2d 99 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
marcel1691 0:2c2b8af11b2d 100 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
marcel1691 0:2c2b8af11b2d 101 * ^ ^ ^ +--+ ^ ^ +--+ ^
marcel1691 0:2c2b8af11b2d 102 * ^ ^ ^ | | ^ ^ | | ^
marcel1691 0:2c2b8af11b2d 103 * Index ------------+ +--------+ +-----------
marcel1691 0:2c2b8af11b2d 104 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
marcel1691 0:2c2b8af11b2d 105 * Pulse count 0 1 2 3 4 5 6 7 8 9 ...
marcel1691 0:2c2b8af11b2d 106 * Rev. count 0 1 2
marcel1691 0:2c2b8af11b2d 107 *
marcel1691 0:2c2b8af11b2d 108 * Rotational position in degrees can be calculated by:
marcel1691 0:2c2b8af11b2d 109 *
marcel1691 0:2c2b8af11b2d 110 * (pulse count / X * N) * 360
marcel1691 0:2c2b8af11b2d 111 *
marcel1691 0:2c2b8af11b2d 112 * Where X is the encoding type [e.g. X4 encoding => X=4], and N is the number
marcel1691 0:2c2b8af11b2d 113 * of pulses per revolution.
marcel1691 0:2c2b8af11b2d 114 *
marcel1691 0:2c2b8af11b2d 115 * Linear position can be calculated by:
marcel1691 0:2c2b8af11b2d 116 *
marcel1691 0:2c2b8af11b2d 117 * (pulse count / X * N) * (1 / PPI)
marcel1691 0:2c2b8af11b2d 118 *
marcel1691 0:2c2b8af11b2d 119 * Where X is encoding type [e.g. X4 encoding => X=44], N is the number of
marcel1691 0:2c2b8af11b2d 120 * pulses per revolution, and PPI is pulses per inch, or the equivalent for
marcel1691 0:2c2b8af11b2d 121 * any other unit of displacement. PPI can be calculated by taking the
marcel1691 0:2c2b8af11b2d 122 * circumference of the wheel or encoder disk and dividing it by the number
marcel1691 0:2c2b8af11b2d 123 * of pulses per revolution.
marcel1691 0:2c2b8af11b2d 124 */
marcel1691 0:2c2b8af11b2d 125
marcel1691 0:2c2b8af11b2d 126 /**
marcel1691 0:2c2b8af11b2d 127 * Includes
marcel1691 0:2c2b8af11b2d 128 */
marcel1691 0:2c2b8af11b2d 129 #include "QEI.h"
marcel1691 0:2c2b8af11b2d 130
marcel1691 0:2c2b8af11b2d 131 QEI::QEI(PinName channelA,
marcel1691 0:2c2b8af11b2d 132 PinName channelB,
marcel1691 0:2c2b8af11b2d 133 PinName index,
marcel1691 0:2c2b8af11b2d 134 int pulsesPerRev,
marcel1691 0:2c2b8af11b2d 135 Encoding encoding) : channelA_(channelA), channelB_(channelB),
marcel1691 0:2c2b8af11b2d 136 index_(index) {
marcel1691 0:2c2b8af11b2d 137
marcel1691 0:2c2b8af11b2d 138 pulses_ = 0;
marcel1691 0:2c2b8af11b2d 139 revolutions_ = 0;
marcel1691 0:2c2b8af11b2d 140 pulsesPerRev_ = pulsesPerRev;
marcel1691 0:2c2b8af11b2d 141 encoding_ = encoding;
marcel1691 0:2c2b8af11b2d 142
marcel1691 0:2c2b8af11b2d 143 //Workout what the current state is.
marcel1691 0:2c2b8af11b2d 144 int chanA = channelA_.read();
marcel1691 0:2c2b8af11b2d 145 int chanB = channelB_.read();
marcel1691 0:2c2b8af11b2d 146
marcel1691 0:2c2b8af11b2d 147 //2-bit state.
marcel1691 0:2c2b8af11b2d 148 currState_ = (chanA << 1) | (chanB);
marcel1691 0:2c2b8af11b2d 149 prevState_ = currState_;
marcel1691 0:2c2b8af11b2d 150
marcel1691 0:2c2b8af11b2d 151 //X2 encoding uses interrupts on only channel A.
marcel1691 0:2c2b8af11b2d 152 //X4 encoding uses interrupts on channel A,
marcel1691 0:2c2b8af11b2d 153 //and on channel B.
marcel1691 0:2c2b8af11b2d 154 channelA_.rise(this, &QEI::encode);
marcel1691 0:2c2b8af11b2d 155 channelA_.fall(this, &QEI::encode);
marcel1691 0:2c2b8af11b2d 156
marcel1691 0:2c2b8af11b2d 157 //If we're using X4 encoding, then attach interrupts to channel B too.
marcel1691 0:2c2b8af11b2d 158 if (encoding == X4_ENCODING) {
marcel1691 0:2c2b8af11b2d 159 channelB_.rise(this, &QEI::encode);
marcel1691 0:2c2b8af11b2d 160 channelB_.fall(this, &QEI::encode);
marcel1691 0:2c2b8af11b2d 161 }
marcel1691 0:2c2b8af11b2d 162 //Index is optional.
marcel1691 0:2c2b8af11b2d 163 if (index != NC) {
marcel1691 0:2c2b8af11b2d 164 index_.rise(this, &QEI::index);
marcel1691 0:2c2b8af11b2d 165 }
marcel1691 0:2c2b8af11b2d 166
marcel1691 0:2c2b8af11b2d 167 }
marcel1691 0:2c2b8af11b2d 168
marcel1691 0:2c2b8af11b2d 169 void QEI::reset(void) {
marcel1691 0:2c2b8af11b2d 170
marcel1691 0:2c2b8af11b2d 171 pulses_ = 0;
marcel1691 0:2c2b8af11b2d 172 revolutions_ = 0;
marcel1691 0:2c2b8af11b2d 173
marcel1691 0:2c2b8af11b2d 174 }
marcel1691 0:2c2b8af11b2d 175
marcel1691 0:2c2b8af11b2d 176 int QEI::getCurrentState(void) {
marcel1691 0:2c2b8af11b2d 177
marcel1691 0:2c2b8af11b2d 178 return currState_;
marcel1691 0:2c2b8af11b2d 179
marcel1691 0:2c2b8af11b2d 180 }
marcel1691 0:2c2b8af11b2d 181
marcel1691 0:2c2b8af11b2d 182 int QEI::getPulses(void) {
marcel1691 0:2c2b8af11b2d 183
marcel1691 0:2c2b8af11b2d 184 return pulses_;
marcel1691 0:2c2b8af11b2d 185
marcel1691 0:2c2b8af11b2d 186 }
marcel1691 0:2c2b8af11b2d 187
marcel1691 0:2c2b8af11b2d 188 int QEI::getRevolutions(void) {
marcel1691 0:2c2b8af11b2d 189
marcel1691 0:2c2b8af11b2d 190 return revolutions_;
marcel1691 0:2c2b8af11b2d 191
marcel1691 0:2c2b8af11b2d 192 }
marcel1691 0:2c2b8af11b2d 193
marcel1691 0:2c2b8af11b2d 194 // +-------------+
marcel1691 0:2c2b8af11b2d 195 // | X2 Encoding |
marcel1691 0:2c2b8af11b2d 196 // +-------------+
marcel1691 0:2c2b8af11b2d 197 //
marcel1691 0:2c2b8af11b2d 198 // When observing states two patterns will appear:
marcel1691 0:2c2b8af11b2d 199 //
marcel1691 0:2c2b8af11b2d 200 // Counter clockwise rotation:
marcel1691 0:2c2b8af11b2d 201 //
marcel1691 0:2c2b8af11b2d 202 // 10 -> 01 -> 10 -> 01 -> ...
marcel1691 0:2c2b8af11b2d 203 //
marcel1691 0:2c2b8af11b2d 204 // Clockwise rotation:
marcel1691 0:2c2b8af11b2d 205 //
marcel1691 0:2c2b8af11b2d 206 // 11 -> 00 -> 11 -> 00 -> ...
marcel1691 0:2c2b8af11b2d 207 //
marcel1691 0:2c2b8af11b2d 208 // We consider counter clockwise rotation to be "forward" and
marcel1691 0:2c2b8af11b2d 209 // counter clockwise to be "backward". Therefore pulse count will increase
marcel1691 0:2c2b8af11b2d 210 // during counter clockwise rotation and decrease during clockwise rotation.
marcel1691 0:2c2b8af11b2d 211 //
marcel1691 0:2c2b8af11b2d 212 // +-------------+
marcel1691 0:2c2b8af11b2d 213 // | X4 Encoding |
marcel1691 0:2c2b8af11b2d 214 // +-------------+
marcel1691 0:2c2b8af11b2d 215 //
marcel1691 0:2c2b8af11b2d 216 // There are four possible states for a quadrature encoder which correspond to
marcel1691 0:2c2b8af11b2d 217 // 2-bit gray code.
marcel1691 0:2c2b8af11b2d 218 //
marcel1691 0:2c2b8af11b2d 219 // A state change is only valid if of only one bit has changed.
marcel1691 0:2c2b8af11b2d 220 // A state change is invalid if both bits have changed.
marcel1691 0:2c2b8af11b2d 221 //
marcel1691 0:2c2b8af11b2d 222 // Clockwise Rotation ->
marcel1691 0:2c2b8af11b2d 223 //
marcel1691 0:2c2b8af11b2d 224 // 00 01 11 10 00
marcel1691 0:2c2b8af11b2d 225 //
marcel1691 0:2c2b8af11b2d 226 // <- Counter Clockwise Rotation
marcel1691 0:2c2b8af11b2d 227 //
marcel1691 0:2c2b8af11b2d 228 // If we observe any valid state changes going from left to right, we have
marcel1691 0:2c2b8af11b2d 229 // moved one pulse clockwise [we will consider this "backward" or "negative"].
marcel1691 0:2c2b8af11b2d 230 //
marcel1691 0:2c2b8af11b2d 231 // If we observe any valid state changes going from right to left we have
marcel1691 0:2c2b8af11b2d 232 // moved one pulse counter clockwise [we will consider this "forward" or
marcel1691 0:2c2b8af11b2d 233 // "positive"].
marcel1691 0:2c2b8af11b2d 234 //
marcel1691 0:2c2b8af11b2d 235 // We might enter an invalid state for a number of reasons which are hard to
marcel1691 0:2c2b8af11b2d 236 // predict - if this is the case, it is generally safe to ignore it, update
marcel1691 0:2c2b8af11b2d 237 // the state and carry on, with the error correcting itself shortly after.
marcel1691 0:2c2b8af11b2d 238 void QEI::encode(void) {
marcel1691 0:2c2b8af11b2d 239
marcel1691 0:2c2b8af11b2d 240 int change = 0;
marcel1691 0:2c2b8af11b2d 241 int chanA = channelA_.read();
marcel1691 0:2c2b8af11b2d 242 int chanB = channelB_.read();
marcel1691 0:2c2b8af11b2d 243
marcel1691 0:2c2b8af11b2d 244 //2-bit state.
marcel1691 0:2c2b8af11b2d 245 currState_ = (chanA << 1) | (chanB);
marcel1691 0:2c2b8af11b2d 246
marcel1691 0:2c2b8af11b2d 247 if (encoding_ == X2_ENCODING) {
marcel1691 0:2c2b8af11b2d 248
marcel1691 0:2c2b8af11b2d 249 //11->00->11->00 is counter clockwise rotation or "forward".
marcel1691 0:2c2b8af11b2d 250 if ((prevState_ == 0x3 && currState_ == 0x0) ||
marcel1691 0:2c2b8af11b2d 251 (prevState_ == 0x0 && currState_ == 0x3)) {
marcel1691 0:2c2b8af11b2d 252
marcel1691 0:2c2b8af11b2d 253 pulses_++;
marcel1691 0:2c2b8af11b2d 254
marcel1691 0:2c2b8af11b2d 255 }
marcel1691 0:2c2b8af11b2d 256 //10->01->10->01 is clockwise rotation or "backward".
marcel1691 0:2c2b8af11b2d 257 else if ((prevState_ == 0x2 && currState_ == 0x1) ||
marcel1691 0:2c2b8af11b2d 258 (prevState_ == 0x1 && currState_ == 0x2)) {
marcel1691 0:2c2b8af11b2d 259
marcel1691 0:2c2b8af11b2d 260 pulses_--;
marcel1691 0:2c2b8af11b2d 261
marcel1691 0:2c2b8af11b2d 262 }
marcel1691 0:2c2b8af11b2d 263
marcel1691 0:2c2b8af11b2d 264 } else if (encoding_ == X4_ENCODING) {
marcel1691 0:2c2b8af11b2d 265
marcel1691 0:2c2b8af11b2d 266 //Entered a new valid state.
marcel1691 0:2c2b8af11b2d 267 if (((currState_ ^ prevState_) != INVALID) && (currState_ != prevState_)) {
marcel1691 0:2c2b8af11b2d 268 //2 bit state. Right hand bit of prev XOR left hand bit of current
marcel1691 0:2c2b8af11b2d 269 //gives 0 if clockwise rotation and 1 if counter clockwise rotation.
marcel1691 0:2c2b8af11b2d 270 change = (prevState_ & PREV_MASK) ^ ((currState_ & CURR_MASK) >> 1);
marcel1691 0:2c2b8af11b2d 271
marcel1691 0:2c2b8af11b2d 272 if (change == 0) {
marcel1691 0:2c2b8af11b2d 273 change = -1;
marcel1691 0:2c2b8af11b2d 274 }
marcel1691 0:2c2b8af11b2d 275
marcel1691 0:2c2b8af11b2d 276 pulses_ -= change;
marcel1691 0:2c2b8af11b2d 277 }
marcel1691 0:2c2b8af11b2d 278
marcel1691 0:2c2b8af11b2d 279 }
marcel1691 0:2c2b8af11b2d 280
marcel1691 0:2c2b8af11b2d 281 prevState_ = currState_;
marcel1691 0:2c2b8af11b2d 282
marcel1691 0:2c2b8af11b2d 283 }
marcel1691 0:2c2b8af11b2d 284
marcel1691 0:2c2b8af11b2d 285 void QEI::index(void) {
marcel1691 0:2c2b8af11b2d 286
marcel1691 0:2c2b8af11b2d 287 revolutions_++;
marcel1691 0:2c2b8af11b2d 288
marcel1691 0:2c2b8af11b2d 289 }