David Smart / QEI

Derivative QEI library to add an error counter and the ability to set the count and revolutions, and reset the error counter.

QEI.cpp@1:cecfd2d4d286, 2021-01-13 (annotated)

Committer:
WiredHome
Date:
Wed Jan 13 20:12:03 2021 +0000
Revision:
1:cecfd2d4d286
Parent:
0:5c2ad81551aa 
Functional version suitable for testing

Who changed what in which revision?

UserRevisionLine numberNew contents of line
aberk 0:5c2ad81551aa 1 /**
aberk 0:5c2ad81551aa 2 * @author Aaron Berk
aberk 0:5c2ad81551aa 3 *
aberk 0:5c2ad81551aa 4 * @section LICENSE
aberk 0:5c2ad81551aa 5 *
WiredHome 1:cecfd2d4d286 6 * Derivative work created in Jan 2021 by D.Smart, which
WiredHome 1:cecfd2d4d286 7 * has the following changes:
WiredHome 1:cecfd2d4d286 8 * + Update for MBED OS 6 ('callback' added to member ISRs)
WiredHome 1:cecfd2d4d286 9 * + Added counter for non-grey-code transitions
WiredHome 1:cecfd2d4d286 10 * + Added set functions to initialize counts to known values
WiredHome 1:cecfd2d4d286 11 * + Added get functions for error counters
WiredHome 1:cecfd2d4d286 12 *
WiredHome 1:cecfd2d4d286 13 * No copyright claim is being made on these changes.
WiredHome 1:cecfd2d4d286 14 *
aberk 0:5c2ad81551aa 15 * Copyright (c) 2010 ARM Limited
aberk 0:5c2ad81551aa 16 *
aberk 0:5c2ad81551aa 17 * Permission is hereby granted, free of charge, to any person obtaining a copy
aberk 0:5c2ad81551aa 18 * of this software and associated documentation files (the "Software"), to deal
aberk 0:5c2ad81551aa 19 * in the Software without restriction, including without limitation the rights
aberk 0:5c2ad81551aa 20 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
aberk 0:5c2ad81551aa 21 * copies of the Software, and to permit persons to whom the Software is
aberk 0:5c2ad81551aa 22 * furnished to do so, subject to the following conditions:
aberk 0:5c2ad81551aa 23 *
aberk 0:5c2ad81551aa 24 * The above copyright notice and this permission notice shall be included in
aberk 0:5c2ad81551aa 25 * all copies or substantial portions of the Software.
aberk 0:5c2ad81551aa 26 *
aberk 0:5c2ad81551aa 27 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
aberk 0:5c2ad81551aa 28 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
aberk 0:5c2ad81551aa 29 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
aberk 0:5c2ad81551aa 30 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
aberk 0:5c2ad81551aa 31 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
aberk 0:5c2ad81551aa 32 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
aberk 0:5c2ad81551aa 33 * THE SOFTWARE.
aberk 0:5c2ad81551aa 34 *
aberk 0:5c2ad81551aa 35 * @section DESCRIPTION
aberk 0:5c2ad81551aa 36 *
aberk 0:5c2ad81551aa 37 * Quadrature Encoder Interface.
aberk 0:5c2ad81551aa 38 *
aberk 0:5c2ad81551aa 39 * A quadrature encoder consists of two code tracks on a disc which are 90
aberk 0:5c2ad81551aa 40 * degrees out of phase. It can be used to determine how far a wheel has
aberk 0:5c2ad81551aa 41 * rotated, relative to a known starting position.
aberk 0:5c2ad81551aa 42 *
aberk 0:5c2ad81551aa 43 * Only one code track changes at a time leading to a more robust system than
aberk 0:5c2ad81551aa 44 * a single track, because any jitter around any edge won't cause a state
aberk 0:5c2ad81551aa 45 * change as the other track will remain constant.
aberk 0:5c2ad81551aa 46 *
aberk 0:5c2ad81551aa 47 * Encoders can be a homebrew affair, consisting of infrared emitters/receivers
aberk 0:5c2ad81551aa 48 * and paper code tracks consisting of alternating black and white sections;
aberk 0:5c2ad81551aa 49 * alternatively, complete disk and PCB emitter/receiver encoder systems can
aberk 0:5c2ad81551aa 50 * be bought, but the interface, regardless of implementation is the same.
aberk 0:5c2ad81551aa 51 *
aberk 0:5c2ad81551aa 52 * +-----+ +-----+ +-----+
aberk 0:5c2ad81551aa 53 * Channel A | ^ | | | | |
aberk 0:5c2ad81551aa 54 * ---+ ^ +-----+ +-----+ +-----
aberk 0:5c2ad81551aa 55 * ^ ^
aberk 0:5c2ad81551aa 56 * ^ +-----+ +-----+ +-----+
aberk 0:5c2ad81551aa 57 * Channel B ^ | | | | | |
aberk 0:5c2ad81551aa 58 * ------+ +-----+ +-----+ +-----
aberk 0:5c2ad81551aa 59 * ^ ^
aberk 0:5c2ad81551aa 60 * ^ ^
aberk 0:5c2ad81551aa 61 * 90deg
aberk 0:5c2ad81551aa 62 *
aberk 0:5c2ad81551aa 63 * The interface uses X2 encoding by default which calculates the pulse count
aberk 0:5c2ad81551aa 64 * based on reading the current state after each rising and falling edge of
aberk 0:5c2ad81551aa 65 * channel A.
aberk 0:5c2ad81551aa 66 *
aberk 0:5c2ad81551aa 67 * +-----+ +-----+ +-----+
aberk 0:5c2ad81551aa 68 * Channel A | | | | | |
aberk 0:5c2ad81551aa 69 * ---+ +-----+ +-----+ +-----
aberk 0:5c2ad81551aa 70 * ^ ^ ^ ^ ^
aberk 0:5c2ad81551aa 71 * ^ +-----+ ^ +-----+ ^ +-----+
aberk 0:5c2ad81551aa 72 * Channel B ^ | ^ | ^ | ^ | ^ | |
aberk 0:5c2ad81551aa 73 * ------+ ^ +-----+ ^ +-----+ +--
aberk 0:5c2ad81551aa 74 * ^ ^ ^ ^ ^
aberk 0:5c2ad81551aa 75 * ^ ^ ^ ^ ^
aberk 0:5c2ad81551aa 76 * Pulse count 0 1 2 3 4 5 ...
aberk 0:5c2ad81551aa 77 *
aberk 0:5c2ad81551aa 78 * This interface can also use X4 encoding which calculates the pulse count
aberk 0:5c2ad81551aa 79 * based on reading the current state after each rising and falling edge of
aberk 0:5c2ad81551aa 80 * either channel.
aberk 0:5c2ad81551aa 81 *
aberk 0:5c2ad81551aa 82 * +-----+ +-----+ +-----+
aberk 0:5c2ad81551aa 83 * Channel A | | | | | |
aberk 0:5c2ad81551aa 84 * ---+ +-----+ +-----+ +-----
aberk 0:5c2ad81551aa 85 * ^ ^ ^ ^ ^
aberk 0:5c2ad81551aa 86 * ^ +-----+ ^ +-----+ ^ +-----+
aberk 0:5c2ad81551aa 87 * Channel B ^ | ^ | ^ | ^ | ^ | |
aberk 0:5c2ad81551aa 88 * ------+ ^ +-----+ ^ +-----+ +--
aberk 0:5c2ad81551aa 89 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
aberk 0:5c2ad81551aa 90 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
aberk 0:5c2ad81551aa 91 * Pulse count 0 1 2 3 4 5 6 7 8 9 ...
aberk 0:5c2ad81551aa 92 *
aberk 0:5c2ad81551aa 93 * It defaults
aberk 0:5c2ad81551aa 94 *
aberk 0:5c2ad81551aa 95 * An optional index channel can be used which determines when a full
aberk 0:5c2ad81551aa 96 * revolution has occured.
aberk 0:5c2ad81551aa 97 *
aberk 0:5c2ad81551aa 98 * If a 4 pules per revolution encoder was used, with X4 encoding,
aberk 0:5c2ad81551aa 99 * the following would be observed.
aberk 0:5c2ad81551aa 100 *
aberk 0:5c2ad81551aa 101 * +-----+ +-----+ +-----+
aberk 0:5c2ad81551aa 102 * Channel A | | | | | |
aberk 0:5c2ad81551aa 103 * ---+ +-----+ +-----+ +-----
aberk 0:5c2ad81551aa 104 * ^ ^ ^ ^ ^
aberk 0:5c2ad81551aa 105 * ^ +-----+ ^ +-----+ ^ +-----+
aberk 0:5c2ad81551aa 106 * Channel B ^ | ^ | ^ | ^ | ^ | |
aberk 0:5c2ad81551aa 107 * ------+ ^ +-----+ ^ +-----+ +--
aberk 0:5c2ad81551aa 108 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
aberk 0:5c2ad81551aa 109 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
aberk 0:5c2ad81551aa 110 * ^ ^ ^ +--+ ^ ^ +--+ ^
aberk 0:5c2ad81551aa 111 * ^ ^ ^ | | ^ ^ | | ^
aberk 0:5c2ad81551aa 112 * Index ------------+ +--------+ +-----------
aberk 0:5c2ad81551aa 113 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
aberk 0:5c2ad81551aa 114 * Pulse count 0 1 2 3 4 5 6 7 8 9 ...
aberk 0:5c2ad81551aa 115 * Rev. count 0 1 2
aberk 0:5c2ad81551aa 116 *
aberk 0:5c2ad81551aa 117 * Rotational position in degrees can be calculated by:
aberk 0:5c2ad81551aa 118 *
aberk 0:5c2ad81551aa 119 * (pulse count / X * N) * 360
aberk 0:5c2ad81551aa 120 *
aberk 0:5c2ad81551aa 121 * Where X is the encoding type [e.g. X4 encoding => X=4], and N is the number
aberk 0:5c2ad81551aa 122 * of pulses per revolution.
aberk 0:5c2ad81551aa 123 *
aberk 0:5c2ad81551aa 124 * Linear position can be calculated by:
aberk 0:5c2ad81551aa 125 *
aberk 0:5c2ad81551aa 126 * (pulse count / X * N) * (1 / PPI)
aberk 0:5c2ad81551aa 127 *
aberk 0:5c2ad81551aa 128 * Where X is encoding type [e.g. X4 encoding => X=44], N is the number of
aberk 0:5c2ad81551aa 129 * pulses per revolution, and PPI is pulses per inch, or the equivalent for
aberk 0:5c2ad81551aa 130 * any other unit of displacement. PPI can be calculated by taking the
aberk 0:5c2ad81551aa 131 * circumference of the wheel or encoder disk and dividing it by the number
aberk 0:5c2ad81551aa 132 * of pulses per revolution.
aberk 0:5c2ad81551aa 133 */
aberk 0:5c2ad81551aa 134
aberk 0:5c2ad81551aa 135 /**
aberk 0:5c2ad81551aa 136 * Includes
aberk 0:5c2ad81551aa 137 */
aberk 0:5c2ad81551aa 138 #include "QEI.h"
aberk 0:5c2ad81551aa 139
aberk 0:5c2ad81551aa 140 QEI::QEI(PinName channelA,
aberk 0:5c2ad81551aa 141 PinName channelB,
aberk 0:5c2ad81551aa 142 PinName index,
aberk 0:5c2ad81551aa 143 int pulsesPerRev,
aberk 0:5c2ad81551aa 144 Encoding encoding) : channelA_(channelA), channelB_(channelB),
aberk 0:5c2ad81551aa 145 index_(index) {
aberk 0:5c2ad81551aa 146
aberk 0:5c2ad81551aa 147 pulses_ = 0;
aberk 0:5c2ad81551aa 148 revolutions_ = 0;
WiredHome 1:cecfd2d4d286 149 invalid_ = 0;
aberk 0:5c2ad81551aa 150 pulsesPerRev_ = pulsesPerRev;
aberk 0:5c2ad81551aa 151 encoding_ = encoding;
aberk 0:5c2ad81551aa 152
aberk 0:5c2ad81551aa 153 //Workout what the current state is.
aberk 0:5c2ad81551aa 154 int chanA = channelA_.read();
aberk 0:5c2ad81551aa 155 int chanB = channelB_.read();
aberk 0:5c2ad81551aa 156
aberk 0:5c2ad81551aa 157 //2-bit state.
aberk 0:5c2ad81551aa 158 currState_ = (chanA << 1) | (chanB);
aberk 0:5c2ad81551aa 159 prevState_ = currState_;
aberk 0:5c2ad81551aa 160
aberk 0:5c2ad81551aa 161 //X2 encoding uses interrupts on only channel A.
aberk 0:5c2ad81551aa 162 //X4 encoding uses interrupts on channel A,
aberk 0:5c2ad81551aa 163 //and on channel B.
WiredHome 1:cecfd2d4d286 164 channelA_.rise(callback(this, &QEI::encode));
WiredHome 1:cecfd2d4d286 165 channelA_.fall(callback(this, &QEI::encode));
aberk 0:5c2ad81551aa 166
aberk 0:5c2ad81551aa 167 //If we're using X4 encoding, then attach interrupts to channel B too.
aberk 0:5c2ad81551aa 168 if (encoding == X4_ENCODING) {
WiredHome 1:cecfd2d4d286 169 channelB_.rise(callback(this, &QEI::encode));
WiredHome 1:cecfd2d4d286 170 channelB_.fall(callback(this, &QEI::encode));
aberk 0:5c2ad81551aa 171 }
aberk 0:5c2ad81551aa 172 //Index is optional.
aberk 0:5c2ad81551aa 173 if (index != NC) {
WiredHome 1:cecfd2d4d286 174 index_.rise(callback(this, &QEI::index));
aberk 0:5c2ad81551aa 175 }
aberk 0:5c2ad81551aa 176
aberk 0:5c2ad81551aa 177 }
aberk 0:5c2ad81551aa 178
WiredHome 1:cecfd2d4d286 179 void QEI::setPulses(int newCount) {
WiredHome 1:cecfd2d4d286 180 pulses_ = newCount;
WiredHome 1:cecfd2d4d286 181 }
WiredHome 1:cecfd2d4d286 182
WiredHome 1:cecfd2d4d286 183 void QEI::setRevolutions(int newRevs) {
WiredHome 1:cecfd2d4d286 184 revolutions_ = newRevs;
WiredHome 1:cecfd2d4d286 185 }
WiredHome 1:cecfd2d4d286 186
aberk 0:5c2ad81551aa 187 void QEI::reset(void) {
aberk 0:5c2ad81551aa 188
aberk 0:5c2ad81551aa 189 pulses_ = 0;
aberk 0:5c2ad81551aa 190 revolutions_ = 0;
WiredHome 1:cecfd2d4d286 191 invalid_ = 0;
aberk 0:5c2ad81551aa 192
aberk 0:5c2ad81551aa 193 }
aberk 0:5c2ad81551aa 194
WiredHome 1:cecfd2d4d286 195 int QEI::getInvalidCount(void) {
WiredHome 1:cecfd2d4d286 196 int r = invalid_;
WiredHome 1:cecfd2d4d286 197 invalid_ = 0;
WiredHome 1:cecfd2d4d286 198 return r;
WiredHome 1:cecfd2d4d286 199 }
WiredHome 1:cecfd2d4d286 200
aberk 0:5c2ad81551aa 201 int QEI::getCurrentState(void) {
aberk 0:5c2ad81551aa 202
aberk 0:5c2ad81551aa 203 return currState_;
aberk 0:5c2ad81551aa 204
aberk 0:5c2ad81551aa 205 }
aberk 0:5c2ad81551aa 206
aberk 0:5c2ad81551aa 207 int QEI::getPulses(void) {
aberk 0:5c2ad81551aa 208
aberk 0:5c2ad81551aa 209 return pulses_;
aberk 0:5c2ad81551aa 210
aberk 0:5c2ad81551aa 211 }
aberk 0:5c2ad81551aa 212
aberk 0:5c2ad81551aa 213 int QEI::getRevolutions(void) {
aberk 0:5c2ad81551aa 214
aberk 0:5c2ad81551aa 215 return revolutions_;
aberk 0:5c2ad81551aa 216
aberk 0:5c2ad81551aa 217 }
aberk 0:5c2ad81551aa 218
aberk 0:5c2ad81551aa 219 // +-------------+
aberk 0:5c2ad81551aa 220 // | X2 Encoding |
aberk 0:5c2ad81551aa 221 // +-------------+
aberk 0:5c2ad81551aa 222 //
aberk 0:5c2ad81551aa 223 // When observing states two patterns will appear:
aberk 0:5c2ad81551aa 224 //
aberk 0:5c2ad81551aa 225 // Counter clockwise rotation:
aberk 0:5c2ad81551aa 226 //
aberk 0:5c2ad81551aa 227 // 10 -> 01 -> 10 -> 01 -> ...
aberk 0:5c2ad81551aa 228 //
aberk 0:5c2ad81551aa 229 // Clockwise rotation:
aberk 0:5c2ad81551aa 230 //
aberk 0:5c2ad81551aa 231 // 11 -> 00 -> 11 -> 00 -> ...
aberk 0:5c2ad81551aa 232 //
aberk 0:5c2ad81551aa 233 // We consider counter clockwise rotation to be "forward" and
aberk 0:5c2ad81551aa 234 // counter clockwise to be "backward". Therefore pulse count will increase
aberk 0:5c2ad81551aa 235 // during counter clockwise rotation and decrease during clockwise rotation.
aberk 0:5c2ad81551aa 236 //
aberk 0:5c2ad81551aa 237 // +-------------+
aberk 0:5c2ad81551aa 238 // | X4 Encoding |
aberk 0:5c2ad81551aa 239 // +-------------+
aberk 0:5c2ad81551aa 240 //
aberk 0:5c2ad81551aa 241 // There are four possible states for a quadrature encoder which correspond to
aberk 0:5c2ad81551aa 242 // 2-bit gray code.
aberk 0:5c2ad81551aa 243 //
aberk 0:5c2ad81551aa 244 // A state change is only valid if of only one bit has changed.
aberk 0:5c2ad81551aa 245 // A state change is invalid if both bits have changed.
aberk 0:5c2ad81551aa 246 //
aberk 0:5c2ad81551aa 247 // Clockwise Rotation ->
aberk 0:5c2ad81551aa 248 //
aberk 0:5c2ad81551aa 249 // 00 01 11 10 00
aberk 0:5c2ad81551aa 250 //
aberk 0:5c2ad81551aa 251 // <- Counter Clockwise Rotation
aberk 0:5c2ad81551aa 252 //
aberk 0:5c2ad81551aa 253 // If we observe any valid state changes going from left to right, we have
aberk 0:5c2ad81551aa 254 // moved one pulse clockwise [we will consider this "backward" or "negative"].
aberk 0:5c2ad81551aa 255 //
aberk 0:5c2ad81551aa 256 // If we observe any valid state changes going from right to left we have
aberk 0:5c2ad81551aa 257 // moved one pulse counter clockwise [we will consider this "forward" or
aberk 0:5c2ad81551aa 258 // "positive"].
aberk 0:5c2ad81551aa 259 //
aberk 0:5c2ad81551aa 260 // We might enter an invalid state for a number of reasons which are hard to
aberk 0:5c2ad81551aa 261 // predict - if this is the case, it is generally safe to ignore it, update
aberk 0:5c2ad81551aa 262 // the state and carry on, with the error correcting itself shortly after.
aberk 0:5c2ad81551aa 263 void QEI::encode(void) {
aberk 0:5c2ad81551aa 264
aberk 0:5c2ad81551aa 265 int change = 0;
aberk 0:5c2ad81551aa 266 int chanA = channelA_.read();
aberk 0:5c2ad81551aa 267 int chanB = channelB_.read();
aberk 0:5c2ad81551aa 268
aberk 0:5c2ad81551aa 269 //2-bit state.
aberk 0:5c2ad81551aa 270 currState_ = (chanA << 1) | (chanB);
aberk 0:5c2ad81551aa 271
aberk 0:5c2ad81551aa 272 if (encoding_ == X2_ENCODING) {
aberk 0:5c2ad81551aa 273
aberk 0:5c2ad81551aa 274 //11->00->11->00 is counter clockwise rotation or "forward".
aberk 0:5c2ad81551aa 275 if ((prevState_ == 0x3 && currState_ == 0x0) ||
aberk 0:5c2ad81551aa 276 (prevState_ == 0x0 && currState_ == 0x3)) {
aberk 0:5c2ad81551aa 277
aberk 0:5c2ad81551aa 278 pulses_++;
aberk 0:5c2ad81551aa 279
aberk 0:5c2ad81551aa 280 }
aberk 0:5c2ad81551aa 281 //10->01->10->01 is clockwise rotation or "backward".
aberk 0:5c2ad81551aa 282 else if ((prevState_ == 0x2 && currState_ == 0x1) ||
aberk 0:5c2ad81551aa 283 (prevState_ == 0x1 && currState_ == 0x2)) {
aberk 0:5c2ad81551aa 284
aberk 0:5c2ad81551aa 285 pulses_--;
aberk 0:5c2ad81551aa 286
aberk 0:5c2ad81551aa 287 }
WiredHome 1:cecfd2d4d286 288 else {
WiredHome 1:cecfd2d4d286 289 invalid_++;
WiredHome 1:cecfd2d4d286 290 }
aberk 0:5c2ad81551aa 291
aberk 0:5c2ad81551aa 292 } else if (encoding_ == X4_ENCODING) {
aberk 0:5c2ad81551aa 293
aberk 0:5c2ad81551aa 294 //Entered a new valid state.
aberk 0:5c2ad81551aa 295 if (((currState_ ^ prevState_) != INVALID) && (currState_ != prevState_)) {
aberk 0:5c2ad81551aa 296 //2 bit state. Right hand bit of prev XOR left hand bit of current
aberk 0:5c2ad81551aa 297 //gives 0 if clockwise rotation and 1 if counter clockwise rotation.
aberk 0:5c2ad81551aa 298 change = (prevState_ & PREV_MASK) ^ ((currState_ & CURR_MASK) >> 1);
aberk 0:5c2ad81551aa 299
aberk 0:5c2ad81551aa 300 if (change == 0) {
aberk 0:5c2ad81551aa 301 change = -1;
aberk 0:5c2ad81551aa 302 }
aberk 0:5c2ad81551aa 303
aberk 0:5c2ad81551aa 304 pulses_ -= change;
aberk 0:5c2ad81551aa 305 }
aberk 0:5c2ad81551aa 306
aberk 0:5c2ad81551aa 307 }
aberk 0:5c2ad81551aa 308
aberk 0:5c2ad81551aa 309 prevState_ = currState_;
aberk 0:5c2ad81551aa 310
aberk 0:5c2ad81551aa 311 }
aberk 0:5c2ad81551aa 312
aberk 0:5c2ad81551aa 313 void QEI::index(void) {
aberk 0:5c2ad81551aa 314
aberk 0:5c2ad81551aa 315 revolutions_++;
aberk 0:5c2ad81551aa 316
aberk 0:5c2ad81551aa 317 }