Sik Chiu Chow / Mbed 2 deprecated encoder01

for 3 encoders

Dependencies:   mbed

QEI.cpp@0:4d7336a951bd, 2021-10-27 (annotated)

Committer:
ea78anana
Date:
Wed Oct 27 05:18:30 2021 +0000
Revision:
0:4d7336a951bd
Child:
1:92fd61600fa8
encoder

Who changed what in which revision?

UserRevisionLine numberNew contents of line
ea78anana 0:4d7336a951bd 1 /**
ea78anana 0:4d7336a951bd 2 * @author Aaron Berk
ea78anana 0:4d7336a951bd 3 *
ea78anana 0:4d7336a951bd 4 * @section LICENSE
ea78anana 0:4d7336a951bd 5 *
ea78anana 0:4d7336a951bd 6 * Copyright (c) 2010 ARM Limited
ea78anana 0:4d7336a951bd 7 *
ea78anana 0:4d7336a951bd 8 * Permission is hereby granted, free of charge, to any person obtaining a copy
ea78anana 0:4d7336a951bd 9 * of this software and associated documentation files (the "Software"), to deal
ea78anana 0:4d7336a951bd 10 * in the Software without restriction, including without limitation the rights
ea78anana 0:4d7336a951bd 11 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
ea78anana 0:4d7336a951bd 12 * copies of the Software, and to permit persons to whom the Software is
ea78anana 0:4d7336a951bd 13 * furnished to do so, subject to the following conditions:
ea78anana 0:4d7336a951bd 14 *
ea78anana 0:4d7336a951bd 15 * The above copyright notice and this permission notice shall be included in
ea78anana 0:4d7336a951bd 16 * all copies or substantial portions of the Software.
ea78anana 0:4d7336a951bd 17 *
ea78anana 0:4d7336a951bd 18 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
ea78anana 0:4d7336a951bd 19 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
ea78anana 0:4d7336a951bd 20 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
ea78anana 0:4d7336a951bd 21 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
ea78anana 0:4d7336a951bd 22 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
ea78anana 0:4d7336a951bd 23 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
ea78anana 0:4d7336a951bd 24 * THE SOFTWARE.
ea78anana 0:4d7336a951bd 25 *
ea78anana 0:4d7336a951bd 26 * @section DESCRIPTION
ea78anana 0:4d7336a951bd 27 *
ea78anana 0:4d7336a951bd 28 * Quadrature Encoder Interface.
ea78anana 0:4d7336a951bd 29 *
ea78anana 0:4d7336a951bd 30 * A quadrature encoder consists of two code tracks on a disc which are 90
ea78anana 0:4d7336a951bd 31 * degrees out of phase. It can be used to determine how far a wheel has
ea78anana 0:4d7336a951bd 32 * rotated, relative to a known starting position.
ea78anana 0:4d7336a951bd 33 *
ea78anana 0:4d7336a951bd 34 * Only one code track changes at a time leading to a more robust system than
ea78anana 0:4d7336a951bd 35 * a single track, because any jitter around any edge won't cause a state
ea78anana 0:4d7336a951bd 36 * change as the other track will remain constant.
ea78anana 0:4d7336a951bd 37 *
ea78anana 0:4d7336a951bd 38 * Encoders can be a homebrew affair, consisting of infrared emitters/receivers
ea78anana 0:4d7336a951bd 39 * and paper code tracks consisting of alternating black and white sections;
ea78anana 0:4d7336a951bd 40 * alternatively, complete disk and PCB emitter/receiver encoder systems can
ea78anana 0:4d7336a951bd 41 * be bought, but the interface, regardless of implementation is the same.
ea78anana 0:4d7336a951bd 42 *
ea78anana 0:4d7336a951bd 43 * +-----+ +-----+ +-----+
ea78anana 0:4d7336a951bd 44 * Channel A | ^ | | | | |
ea78anana 0:4d7336a951bd 45 * ---+ ^ +-----+ +-----+ +-----
ea78anana 0:4d7336a951bd 46 * ^ ^
ea78anana 0:4d7336a951bd 47 * ^ +-----+ +-----+ +-----+
ea78anana 0:4d7336a951bd 48 * Channel B ^ | | | | | |
ea78anana 0:4d7336a951bd 49 * ------+ +-----+ +-----+ +-----
ea78anana 0:4d7336a951bd 50 * ^ ^
ea78anana 0:4d7336a951bd 51 * ^ ^
ea78anana 0:4d7336a951bd 52 * 90deg
ea78anana 0:4d7336a951bd 53 *
ea78anana 0:4d7336a951bd 54 * The interface uses X2 encoding by default which calculates the pulse count
ea78anana 0:4d7336a951bd 55 * based on reading the current state after each rising and falling edge of
ea78anana 0:4d7336a951bd 56 * channel A.
ea78anana 0:4d7336a951bd 57 *
ea78anana 0:4d7336a951bd 58 * +-----+ +-----+ +-----+
ea78anana 0:4d7336a951bd 59 * Channel A | | | | | |
ea78anana 0:4d7336a951bd 60 * ---+ +-----+ +-----+ +-----
ea78anana 0:4d7336a951bd 61 * ^ ^ ^ ^ ^
ea78anana 0:4d7336a951bd 62 * ^ +-----+ ^ +-----+ ^ +-----+
ea78anana 0:4d7336a951bd 63 * Channel B ^ | ^ | ^ | ^ | ^ | |
ea78anana 0:4d7336a951bd 64 * ------+ ^ +-----+ ^ +-----+ +--
ea78anana 0:4d7336a951bd 65 * ^ ^ ^ ^ ^
ea78anana 0:4d7336a951bd 66 * ^ ^ ^ ^ ^
ea78anana 0:4d7336a951bd 67 * Pulse count 0 1 2 3 4 5 ...
ea78anana 0:4d7336a951bd 68 *
ea78anana 0:4d7336a951bd 69 * This interface can also use X4 encoding which calculates the pulse count
ea78anana 0:4d7336a951bd 70 * based on reading the current state after each rising and falling edge of
ea78anana 0:4d7336a951bd 71 * either channel.
ea78anana 0:4d7336a951bd 72 *
ea78anana 0:4d7336a951bd 73 * +-----+ +-----+ +-----+
ea78anana 0:4d7336a951bd 74 * Channel A | | | | | |
ea78anana 0:4d7336a951bd 75 * ---+ +-----+ +-----+ +-----
ea78anana 0:4d7336a951bd 76 * ^ ^ ^ ^ ^
ea78anana 0:4d7336a951bd 77 * ^ +-----+ ^ +-----+ ^ +-----+
ea78anana 0:4d7336a951bd 78 * Channel B ^ | ^ | ^ | ^ | ^ | |
ea78anana 0:4d7336a951bd 79 * ------+ ^ +-----+ ^ +-----+ +--
ea78anana 0:4d7336a951bd 80 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
ea78anana 0:4d7336a951bd 81 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
ea78anana 0:4d7336a951bd 82 * Pulse count 0 1 2 3 4 5 6 7 8 9 ...
ea78anana 0:4d7336a951bd 83 *
ea78anana 0:4d7336a951bd 84 * It defaults
ea78anana 0:4d7336a951bd 85 *
ea78anana 0:4d7336a951bd 86 * An optional index channel can be used which determines when a full
ea78anana 0:4d7336a951bd 87 * revolution has occured.
ea78anana 0:4d7336a951bd 88 *
ea78anana 0:4d7336a951bd 89 * If a 4 pules per revolution encoder was used, with X4 encoding,
ea78anana 0:4d7336a951bd 90 * the following would be observed.
ea78anana 0:4d7336a951bd 91 *
ea78anana 0:4d7336a951bd 92 * +-----+ +-----+ +-----+
ea78anana 0:4d7336a951bd 93 * Channel A | | | | | |
ea78anana 0:4d7336a951bd 94 * ---+ +-----+ +-----+ +-----
ea78anana 0:4d7336a951bd 95 * ^ ^ ^ ^ ^
ea78anana 0:4d7336a951bd 96 * ^ +-----+ ^ +-----+ ^ +-----+
ea78anana 0:4d7336a951bd 97 * Channel B ^ | ^ | ^ | ^ | ^ | |
ea78anana 0:4d7336a951bd 98 * ------+ ^ +-----+ ^ +-----+ +--
ea78anana 0:4d7336a951bd 99 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
ea78anana 0:4d7336a951bd 100 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
ea78anana 0:4d7336a951bd 101 * ^ ^ ^ +--+ ^ ^ +--+ ^
ea78anana 0:4d7336a951bd 102 * ^ ^ ^ | | ^ ^ | | ^
ea78anana 0:4d7336a951bd 103 * Index ------------+ +--------+ +-----------
ea78anana 0:4d7336a951bd 104 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
ea78anana 0:4d7336a951bd 105 * Pulse count 0 1 2 3 4 5 6 7 8 9 ...
ea78anana 0:4d7336a951bd 106 * Rev. count 0 1 2
ea78anana 0:4d7336a951bd 107 *
ea78anana 0:4d7336a951bd 108 * Rotational position in degrees can be calculated by:
ea78anana 0:4d7336a951bd 109 *
ea78anana 0:4d7336a951bd 110 * (pulse count / X * N) * 360
ea78anana 0:4d7336a951bd 111 *
ea78anana 0:4d7336a951bd 112 * Where X is the encoding type [e.g. X4 encoding => X=4], and N is the number
ea78anana 0:4d7336a951bd 113 * of pulses per revolution.
ea78anana 0:4d7336a951bd 114 *
ea78anana 0:4d7336a951bd 115 * Linear position can be calculated by:
ea78anana 0:4d7336a951bd 116 *
ea78anana 0:4d7336a951bd 117 * (pulse count / X * N) * (1 / PPI)
ea78anana 0:4d7336a951bd 118 *
ea78anana 0:4d7336a951bd 119 * Where X is encoding type [e.g. X4 encoding => X=44], N is the number of
ea78anana 0:4d7336a951bd 120 * pulses per revolution, and PPI is pulses per inch, or the equivalent for
ea78anana 0:4d7336a951bd 121 * any other unit of displacement. PPI can be calculated by taking the
ea78anana 0:4d7336a951bd 122 * circumference of the wheel or encoder disk and dividing it by the number
ea78anana 0:4d7336a951bd 123 * of pulses per revolution.
ea78anana 0:4d7336a951bd 124 */
ea78anana 0:4d7336a951bd 125
ea78anana 0:4d7336a951bd 126 /**
ea78anana 0:4d7336a951bd 127 * Includes
ea78anana 0:4d7336a951bd 128 */
ea78anana 0:4d7336a951bd 129 #include "QEI.h"
ea78anana 0:4d7336a951bd 130
ea78anana 0:4d7336a951bd 131 QEI::QEI(PinName channelA,
ea78anana 0:4d7336a951bd 132 PinName channelB,
ea78anana 0:4d7336a951bd 133 PinName index,
ea78anana 0:4d7336a951bd 134 int pulsesPerRev,
ea78anana 0:4d7336a951bd 135 Encoding encoding) : channelA_(channelA), channelB_(channelB),
ea78anana 0:4d7336a951bd 136 index_(index) {
ea78anana 0:4d7336a951bd 137
ea78anana 0:4d7336a951bd 138 pulses_ = 0;
ea78anana 0:4d7336a951bd 139 revolutions_ = 0;
ea78anana 0:4d7336a951bd 140 pulsesPerRev_ = pulsesPerRev;
ea78anana 0:4d7336a951bd 141 encoding_ = encoding;
ea78anana 0:4d7336a951bd 142
ea78anana 0:4d7336a951bd 143 //Workout what the current state is.
ea78anana 0:4d7336a951bd 144 int chanA = channelA_.read();
ea78anana 0:4d7336a951bd 145 int chanB = channelB_.read();
ea78anana 0:4d7336a951bd 146
ea78anana 0:4d7336a951bd 147 //2-bit state.
ea78anana 0:4d7336a951bd 148 currState_ = (chanA << 1) | (chanB);
ea78anana 0:4d7336a951bd 149 prevState_ = currState_;
ea78anana 0:4d7336a951bd 150
ea78anana 0:4d7336a951bd 151 //X2 encoding uses interrupts on only channel A.
ea78anana 0:4d7336a951bd 152 //X4 encoding uses interrupts on channel A,
ea78anana 0:4d7336a951bd 153 //and on channel B.
ea78anana 0:4d7336a951bd 154 channelA_.rise(this, &QEI::encode);
ea78anana 0:4d7336a951bd 155 channelA_.fall(this, &QEI::encode);
ea78anana 0:4d7336a951bd 156
ea78anana 0:4d7336a951bd 157 //If we're using X4 encoding, then attach interrupts to channel B too.
ea78anana 0:4d7336a951bd 158 if (encoding == X4_ENCODING) {
ea78anana 0:4d7336a951bd 159 channelB_.rise(this, &QEI::encode);
ea78anana 0:4d7336a951bd 160 channelB_.fall(this, &QEI::encode);
ea78anana 0:4d7336a951bd 161 }
ea78anana 0:4d7336a951bd 162 //Index is optional.
ea78anana 0:4d7336a951bd 163 if (index != NC) {
ea78anana 0:4d7336a951bd 164 index_.rise(this, &QEI::index);
ea78anana 0:4d7336a951bd 165 }
ea78anana 0:4d7336a951bd 166
ea78anana 0:4d7336a951bd 167 }
ea78anana 0:4d7336a951bd 168
ea78anana 0:4d7336a951bd 169 void QEI::reset(void) {
ea78anana 0:4d7336a951bd 170
ea78anana 0:4d7336a951bd 171 pulses_ = 0;
ea78anana 0:4d7336a951bd 172 revolutions_ = 0;
ea78anana 0:4d7336a951bd 173
ea78anana 0:4d7336a951bd 174 }
ea78anana 0:4d7336a951bd 175
ea78anana 0:4d7336a951bd 176 int QEI::getCurrentState(void) {
ea78anana 0:4d7336a951bd 177
ea78anana 0:4d7336a951bd 178 return currState_;
ea78anana 0:4d7336a951bd 179
ea78anana 0:4d7336a951bd 180 }
ea78anana 0:4d7336a951bd 181
ea78anana 0:4d7336a951bd 182 int QEI::getPulses(void) {
ea78anana 0:4d7336a951bd 183
ea78anana 0:4d7336a951bd 184 return pulses_;
ea78anana 0:4d7336a951bd 185
ea78anana 0:4d7336a951bd 186 }
ea78anana 0:4d7336a951bd 187
ea78anana 0:4d7336a951bd 188 int QEI::getRevolutions(void) {
ea78anana 0:4d7336a951bd 189
ea78anana 0:4d7336a951bd 190 return revolutions_;
ea78anana 0:4d7336a951bd 191
ea78anana 0:4d7336a951bd 192 }
ea78anana 0:4d7336a951bd 193
ea78anana 0:4d7336a951bd 194 // +-------------+
ea78anana 0:4d7336a951bd 195 // | X2 Encoding |
ea78anana 0:4d7336a951bd 196 // +-------------+
ea78anana 0:4d7336a951bd 197 //
ea78anana 0:4d7336a951bd 198 // When observing states two patterns will appear:
ea78anana 0:4d7336a951bd 199 //
ea78anana 0:4d7336a951bd 200 // Counter clockwise rotation:
ea78anana 0:4d7336a951bd 201 //
ea78anana 0:4d7336a951bd 202 // 10 -> 01 -> 10 -> 01 -> ...
ea78anana 0:4d7336a951bd 203 //
ea78anana 0:4d7336a951bd 204 // Clockwise rotation:
ea78anana 0:4d7336a951bd 205 //
ea78anana 0:4d7336a951bd 206 // 11 -> 00 -> 11 -> 00 -> ...
ea78anana 0:4d7336a951bd 207 //
ea78anana 0:4d7336a951bd 208 // We consider counter clockwise rotation to be "forward" and
ea78anana 0:4d7336a951bd 209 // counter clockwise to be "backward". Therefore pulse count will increase
ea78anana 0:4d7336a951bd 210 // during counter clockwise rotation and decrease during clockwise rotation.
ea78anana 0:4d7336a951bd 211 //
ea78anana 0:4d7336a951bd 212 // +-------------+
ea78anana 0:4d7336a951bd 213 // | X4 Encoding |
ea78anana 0:4d7336a951bd 214 // +-------------+
ea78anana 0:4d7336a951bd 215 //
ea78anana 0:4d7336a951bd 216 // There are four possible states for a quadrature encoder which correspond to
ea78anana 0:4d7336a951bd 217 // 2-bit gray code.
ea78anana 0:4d7336a951bd 218 //
ea78anana 0:4d7336a951bd 219 // A state change is only valid if of only one bit has changed.
ea78anana 0:4d7336a951bd 220 // A state change is invalid if both bits have changed.
ea78anana 0:4d7336a951bd 221 //
ea78anana 0:4d7336a951bd 222 // Clockwise Rotation ->
ea78anana 0:4d7336a951bd 223 //
ea78anana 0:4d7336a951bd 224 // 00 01 11 10 00
ea78anana 0:4d7336a951bd 225 //
ea78anana 0:4d7336a951bd 226 // <- Counter Clockwise Rotation
ea78anana 0:4d7336a951bd 227 //
ea78anana 0:4d7336a951bd 228 // If we observe any valid state changes going from left to right, we have
ea78anana 0:4d7336a951bd 229 // moved one pulse clockwise [we will consider this "backward" or "negative"].
ea78anana 0:4d7336a951bd 230 //
ea78anana 0:4d7336a951bd 231 // If we observe any valid state changes going from right to left we have
ea78anana 0:4d7336a951bd 232 // moved one pulse counter clockwise [we will consider this "forward" or
ea78anana 0:4d7336a951bd 233 // "positive"].
ea78anana 0:4d7336a951bd 234 //
ea78anana 0:4d7336a951bd 235 // We might enter an invalid state for a number of reasons which are hard to
ea78anana 0:4d7336a951bd 236 // predict - if this is the case, it is generally safe to ignore it, update
ea78anana 0:4d7336a951bd 237 // the state and carry on, with the error correcting itself shortly after.
ea78anana 0:4d7336a951bd 238 void QEI::encode(void) {
ea78anana 0:4d7336a951bd 239
ea78anana 0:4d7336a951bd 240 int change = 0;
ea78anana 0:4d7336a951bd 241 int chanA = channelA_.read();
ea78anana 0:4d7336a951bd 242 int chanB = channelB_.read();
ea78anana 0:4d7336a951bd 243
ea78anana 0:4d7336a951bd 244 //2-bit state.
ea78anana 0:4d7336a951bd 245 currState_ = (chanA << 1) | (chanB);
ea78anana 0:4d7336a951bd 246
ea78anana 0:4d7336a951bd 247 if (encoding_ == X2_ENCODING) {
ea78anana 0:4d7336a951bd 248
ea78anana 0:4d7336a951bd 249 //11->00->11->00 is counter clockwise rotation or "forward".
ea78anana 0:4d7336a951bd 250 if ((prevState_ == 0x3 && currState_ == 0x0) ||
ea78anana 0:4d7336a951bd 251 (prevState_ == 0x0 && currState_ == 0x3)) {
ea78anana 0:4d7336a951bd 252
ea78anana 0:4d7336a951bd 253 pulses_++;
ea78anana 0:4d7336a951bd 254
ea78anana 0:4d7336a951bd 255 }
ea78anana 0:4d7336a951bd 256 //10->01->10->01 is clockwise rotation or "backward".
ea78anana 0:4d7336a951bd 257 else if ((prevState_ == 0x2 && currState_ == 0x1) ||
ea78anana 0:4d7336a951bd 258 (prevState_ == 0x1 && currState_ == 0x2)) {
ea78anana 0:4d7336a951bd 259
ea78anana 0:4d7336a951bd 260 pulses_--;
ea78anana 0:4d7336a951bd 261
ea78anana 0:4d7336a951bd 262 }
ea78anana 0:4d7336a951bd 263
ea78anana 0:4d7336a951bd 264 } else if (encoding_ == X4_ENCODING) {
ea78anana 0:4d7336a951bd 265
ea78anana 0:4d7336a951bd 266 //Entered a new valid state.
ea78anana 0:4d7336a951bd 267 if (((currState_ ^ prevState_) != INVALID) && (currState_ != prevState_)) {
ea78anana 0:4d7336a951bd 268 //2 bit state. Right hand bit of prev XOR left hand bit of current
ea78anana 0:4d7336a951bd 269 //gives 0 if clockwise rotation and 1 if counter clockwise rotation.
ea78anana 0:4d7336a951bd 270 change = (prevState_ & PREV_MASK) ^ ((currState_ & CURR_MASK) >> 1);
ea78anana 0:4d7336a951bd 271
ea78anana 0:4d7336a951bd 272 if (change == 0) {
ea78anana 0:4d7336a951bd 273 change = -1;
ea78anana 0:4d7336a951bd 274 }
ea78anana 0:4d7336a951bd 275
ea78anana 0:4d7336a951bd 276 pulses_ -= change;
ea78anana 0:4d7336a951bd 277 }
ea78anana 0:4d7336a951bd 278
ea78anana 0:4d7336a951bd 279 }
ea78anana 0:4d7336a951bd 280
ea78anana 0:4d7336a951bd 281 prevState_ = currState_;
ea78anana 0:4d7336a951bd 282
ea78anana 0:4d7336a951bd 283 }
ea78anana 0:4d7336a951bd 284
ea78anana 0:4d7336a951bd 285 void QEI::index(void) {
ea78anana 0:4d7336a951bd 286
ea78anana 0:4d7336a951bd 287 revolutions_++;
ea78anana 0:4d7336a951bd 288
ea78anana 0:4d7336a951bd 289 }
ea78anana 0:4d7336a951bd 290