jiexuan fan / QEI

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QEI.h@0:5c2ad81551aa, 2010-09-02 (annotated)

Committer:
aberk
Date:
Thu Sep 02 16:48:55 2010 +0000
Revision:
0:5c2ad81551aa
Child:
1:3e8503217113
Added X2 encoding, which the library now uses by default. This reduces the number of interrupts generated.

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 *
aberk 0:5c2ad81551aa 6 * Copyright (c) 2010 ARM Limited
aberk 0:5c2ad81551aa 7 *
aberk 0:5c2ad81551aa 8 * Permission is hereby granted, free of charge, to any person obtaining a copy
aberk 0:5c2ad81551aa 9 * of this software and associated documentation files (the "Software"), to deal
aberk 0:5c2ad81551aa 10 * in the Software without restriction, including without limitation the rights
aberk 0:5c2ad81551aa 11 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
aberk 0:5c2ad81551aa 12 * copies of the Software, and to permit persons to whom the Software is
aberk 0:5c2ad81551aa 13 * furnished to do so, subject to the following conditions:
aberk 0:5c2ad81551aa 14 *
aberk 0:5c2ad81551aa 15 * The above copyright notice and this permission notice shall be included in
aberk 0:5c2ad81551aa 16 * all copies or substantial portions of the Software.
aberk 0:5c2ad81551aa 17 *
aberk 0:5c2ad81551aa 18 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
aberk 0:5c2ad81551aa 19 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
aberk 0:5c2ad81551aa 20 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
aberk 0:5c2ad81551aa 21 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
aberk 0:5c2ad81551aa 22 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
aberk 0:5c2ad81551aa 23 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
aberk 0:5c2ad81551aa 24 * THE SOFTWARE.
aberk 0:5c2ad81551aa 25 *
aberk 0:5c2ad81551aa 26 * @section DESCRIPTION
aberk 0:5c2ad81551aa 27 *
aberk 0:5c2ad81551aa 28 * Quadrature Encoder Interface.
aberk 0:5c2ad81551aa 29 *
aberk 0:5c2ad81551aa 30 * A quadrature encoder consists of two code tracks on a disc which are 90
aberk 0:5c2ad81551aa 31 * degrees out of phase. It can be used to determine how far a wheel has
aberk 0:5c2ad81551aa 32 * rotated, relative to a known starting position.
aberk 0:5c2ad81551aa 33 *
aberk 0:5c2ad81551aa 34 * Only one code track changes at a time leading to a more robust system than
aberk 0:5c2ad81551aa 35 * a single track, because any jitter around any edge won't cause a state
aberk 0:5c2ad81551aa 36 * change as the other track will remain constant.
aberk 0:5c2ad81551aa 37 *
aberk 0:5c2ad81551aa 38 * Encoders can be a homebrew affair, consisting of infrared emitters/receivers
aberk 0:5c2ad81551aa 39 * and paper code tracks consisting of alternating black and white sections;
aberk 0:5c2ad81551aa 40 * alternatively, complete disk and PCB emitter/receiver encoder systems can
aberk 0:5c2ad81551aa 41 * be bought, but the interface, regardless of implementation is the same.
aberk 0:5c2ad81551aa 42 *
aberk 0:5c2ad81551aa 43 * +-----+ +-----+ +-----+
aberk 0:5c2ad81551aa 44 * Channel A | ^ | | | | |
aberk 0:5c2ad81551aa 45 * ---+ ^ +-----+ +-----+ +-----
aberk 0:5c2ad81551aa 46 * ^ ^
aberk 0:5c2ad81551aa 47 * ^ +-----+ +-----+ +-----+
aberk 0:5c2ad81551aa 48 * Channel B ^ | | | | | |
aberk 0:5c2ad81551aa 49 * ------+ +-----+ +-----+ +-----
aberk 0:5c2ad81551aa 50 * ^ ^
aberk 0:5c2ad81551aa 51 * ^ ^
aberk 0:5c2ad81551aa 52 * 90deg
aberk 0:5c2ad81551aa 53 *
aberk 0:5c2ad81551aa 54 * The interface uses X2 encoding by default which calculates the pulse count
aberk 0:5c2ad81551aa 55 * based on reading the current state after each rising and falling edge of
aberk 0:5c2ad81551aa 56 * channel A.
aberk 0:5c2ad81551aa 57 *
aberk 0:5c2ad81551aa 58 * +-----+ +-----+ +-----+
aberk 0:5c2ad81551aa 59 * Channel A | | | | | |
aberk 0:5c2ad81551aa 60 * ---+ +-----+ +-----+ +-----
aberk 0:5c2ad81551aa 61 * ^ ^ ^ ^ ^
aberk 0:5c2ad81551aa 62 * ^ +-----+ ^ +-----+ ^ +-----+
aberk 0:5c2ad81551aa 63 * Channel B ^ | ^ | ^ | ^ | ^ | |
aberk 0:5c2ad81551aa 64 * ------+ ^ +-----+ ^ +-----+ +--
aberk 0:5c2ad81551aa 65 * ^ ^ ^ ^ ^
aberk 0:5c2ad81551aa 66 * ^ ^ ^ ^ ^
aberk 0:5c2ad81551aa 67 * Pulse count 0 1 2 3 4 5 ...
aberk 0:5c2ad81551aa 68 *
aberk 0:5c2ad81551aa 69 * This interface can also use X4 encoding which calculates the pulse count
aberk 0:5c2ad81551aa 70 * based on reading the current state after each rising and falling edge of
aberk 0:5c2ad81551aa 71 * either channel.
aberk 0:5c2ad81551aa 72 *
aberk 0:5c2ad81551aa 73 * +-----+ +-----+ +-----+
aberk 0:5c2ad81551aa 74 * Channel A | | | | | |
aberk 0:5c2ad81551aa 75 * ---+ +-----+ +-----+ +-----
aberk 0:5c2ad81551aa 76 * ^ ^ ^ ^ ^
aberk 0:5c2ad81551aa 77 * ^ +-----+ ^ +-----+ ^ +-----+
aberk 0:5c2ad81551aa 78 * Channel B ^ | ^ | ^ | ^ | ^ | |
aberk 0:5c2ad81551aa 79 * ------+ ^ +-----+ ^ +-----+ +--
aberk 0:5c2ad81551aa 80 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
aberk 0:5c2ad81551aa 81 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
aberk 0:5c2ad81551aa 82 * Pulse count 0 1 2 3 4 5 6 7 8 9 ...
aberk 0:5c2ad81551aa 83 *
aberk 0:5c2ad81551aa 84 * It defaults
aberk 0:5c2ad81551aa 85 *
aberk 0:5c2ad81551aa 86 * An optional index channel can be used which determines when a full
aberk 0:5c2ad81551aa 87 * revolution has occured.
aberk 0:5c2ad81551aa 88 *
aberk 0:5c2ad81551aa 89 * If a 4 pules per revolution encoder was used, with X4 encoding,
aberk 0:5c2ad81551aa 90 * the following would be observed.
aberk 0:5c2ad81551aa 91 *
aberk 0:5c2ad81551aa 92 * +-----+ +-----+ +-----+
aberk 0:5c2ad81551aa 93 * Channel A | | | | | |
aberk 0:5c2ad81551aa 94 * ---+ +-----+ +-----+ +-----
aberk 0:5c2ad81551aa 95 * ^ ^ ^ ^ ^
aberk 0:5c2ad81551aa 96 * ^ +-----+ ^ +-----+ ^ +-----+
aberk 0:5c2ad81551aa 97 * Channel B ^ | ^ | ^ | ^ | ^ | |
aberk 0:5c2ad81551aa 98 * ------+ ^ +-----+ ^ +-----+ +--
aberk 0:5c2ad81551aa 99 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
aberk 0:5c2ad81551aa 100 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
aberk 0:5c2ad81551aa 101 * ^ ^ ^ +--+ ^ ^ +--+ ^
aberk 0:5c2ad81551aa 102 * ^ ^ ^ | | ^ ^ | | ^
aberk 0:5c2ad81551aa 103 * Index ------------+ +--------+ +-----------
aberk 0:5c2ad81551aa 104 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
aberk 0:5c2ad81551aa 105 * Pulse count 0 1 2 3 4 5 6 7 8 9 ...
aberk 0:5c2ad81551aa 106 * Rev. count 0 1 2
aberk 0:5c2ad81551aa 107 *
aberk 0:5c2ad81551aa 108 * Rotational position in degrees can be calculated by:
aberk 0:5c2ad81551aa 109 *
aberk 0:5c2ad81551aa 110 * (pulse count / X * N) * 360
aberk 0:5c2ad81551aa 111 *
aberk 0:5c2ad81551aa 112 * Where X is the encoding type [e.g. X4 encoding => X=4], and N is the number
aberk 0:5c2ad81551aa 113 * of pulses per revolution.
aberk 0:5c2ad81551aa 114 *
aberk 0:5c2ad81551aa 115 * Linear position can be calculated by:
aberk 0:5c2ad81551aa 116 *
aberk 0:5c2ad81551aa 117 * (pulse count / X * N) * (1 / PPI)
aberk 0:5c2ad81551aa 118 *
aberk 0:5c2ad81551aa 119 * Where X is encoding type [e.g. X4 encoding => X=44], N is the number of
aberk 0:5c2ad81551aa 120 * pulses per revolution, and PPI is pulses per inch, or the equivalent for
aberk 0:5c2ad81551aa 121 * any other unit of displacement. PPI can be calculated by taking the
aberk 0:5c2ad81551aa 122 * circumference of the wheel or encoder disk and dividing it by the number
aberk 0:5c2ad81551aa 123 * of pulses per revolution.
aberk 0:5c2ad81551aa 124 */
aberk 0:5c2ad81551aa 125
aberk 0:5c2ad81551aa 126 #ifndef QEI_H
aberk 0:5c2ad81551aa 127 #define QEI_H
aberk 0:5c2ad81551aa 128
aberk 0:5c2ad81551aa 129 /**
aberk 0:5c2ad81551aa 130 * Includes
aberk 0:5c2ad81551aa 131 */
aberk 0:5c2ad81551aa 132 #include "mbed.h"
aberk 0:5c2ad81551aa 133
aberk 0:5c2ad81551aa 134 /**
aberk 0:5c2ad81551aa 135 * Defines
aberk 0:5c2ad81551aa 136 */
aberk 0:5c2ad81551aa 137 #define PREV_MASK 0x1 //Mask for the previous state in determining direction
aberk 0:5c2ad81551aa 138 //of rotation.
aberk 0:5c2ad81551aa 139 #define CURR_MASK 0x2 //Mask for the current state in determining direction
aberk 0:5c2ad81551aa 140 //of rotation.
aberk 0:5c2ad81551aa 141 #define INVALID 0x3 //XORing two states where both bits have changed.
aberk 0:5c2ad81551aa 142
aberk 0:5c2ad81551aa 143 /**
aberk 0:5c2ad81551aa 144 * Quadrature Encoder Interface.
aberk 0:5c2ad81551aa 145 */
aberk 0:5c2ad81551aa 146 class QEI {
aberk 0:5c2ad81551aa 147
aberk 0:5c2ad81551aa 148 public:
aberk 0:5c2ad81551aa 149
aberk 0:5c2ad81551aa 150 typedef enum Encoding {
aberk 0:5c2ad81551aa 151
aberk 0:5c2ad81551aa 152 X2_ENCODING,
aberk 0:5c2ad81551aa 153 X4_ENCODING
aberk 0:5c2ad81551aa 154
aberk 0:5c2ad81551aa 155 } Encoding;
aberk 0:5c2ad81551aa 156
aberk 0:5c2ad81551aa 157 /**
aberk 0:5c2ad81551aa 158 * Constructor.
aberk 0:5c2ad81551aa 159 *
aberk 0:5c2ad81551aa 160 * Reads the current values on channel A and channel B to determine the
aberk 0:5c2ad81551aa 161 * initial state.
aberk 0:5c2ad81551aa 162 *
aberk 0:5c2ad81551aa 163 * Attaches the encode function to the rise/fall interrupt edges of
aberk 0:5c2ad81551aa 164 * channels A and B to perform X4 encoding.
aberk 0:5c2ad81551aa 165 *
aberk 0:5c2ad81551aa 166 * Attaches the index function to the rise interrupt edge of channel index
aberk 0:5c2ad81551aa 167 * (if it is used) to count revolutions.
aberk 0:5c2ad81551aa 168 *
aberk 0:5c2ad81551aa 169 * @param channelA mbed pin for channel A input.
aberk 0:5c2ad81551aa 170 * @param channelB mbed pin for channel B input.
aberk 0:5c2ad81551aa 171 * @param index mbed pin for optional index channel input,
aberk 0:5c2ad81551aa 172 * (pass NC if not needed).
aberk 0:5c2ad81551aa 173 * @param pulsesPerRev Number of pulses in one revolution.
aberk 0:5c2ad81551aa 174 * @param encoding The encoding to use. Uses X2 encoding by default. X2
aberk 0:5c2ad81551aa 175 * encoding uses interrupts on the rising and falling edges
aberk 0:5c2ad81551aa 176 * of only channel A where as X4 uses them on both
aberk 0:5c2ad81551aa 177 * channels.
aberk 0:5c2ad81551aa 178 */
aberk 0:5c2ad81551aa 179 QEI(PinName channelA, PinName channelB, PinName index, int pulsesPerRev, Encoding encoding = X2_ENCODING);
aberk 0:5c2ad81551aa 180
aberk 0:5c2ad81551aa 181 /**
aberk 0:5c2ad81551aa 182 * Reset the encoder.
aberk 0:5c2ad81551aa 183 *
aberk 0:5c2ad81551aa 184 * Sets the pulses and revolutions count to zero.
aberk 0:5c2ad81551aa 185 */
aberk 0:5c2ad81551aa 186 void reset(void);
aberk 0:5c2ad81551aa 187
aberk 0:5c2ad81551aa 188 /**
aberk 0:5c2ad81551aa 189 * Read the state of the encoder.
aberk 0:5c2ad81551aa 190 *
aberk 0:5c2ad81551aa 191 * @return The current state of the encoder as a 2-bit number, where:
aberk 0:5c2ad81551aa 192 * bit 1 = The reading from channel B
aberk 0:5c2ad81551aa 193 * bit 2 = The reading from channel A
aberk 0:5c2ad81551aa 194 */
aberk 0:5c2ad81551aa 195 int getCurrentState(void);
aberk 0:5c2ad81551aa 196
aberk 0:5c2ad81551aa 197 /**
aberk 0:5c2ad81551aa 198 * Read the number of pulses recorded by the encoder.
aberk 0:5c2ad81551aa 199 *
aberk 0:5c2ad81551aa 200 * @return Number of pulses which have occured.
aberk 0:5c2ad81551aa 201 */
aberk 0:5c2ad81551aa 202 int getPulses(void);
aberk 0:5c2ad81551aa 203
aberk 0:5c2ad81551aa 204 /**
aberk 0:5c2ad81551aa 205 * Read the number of revolutions recorded by the encoder on the index channel.
aberk 0:5c2ad81551aa 206 *
aberk 0:5c2ad81551aa 207 * @return Number of revolutions which have occured on the index channel.
aberk 0:5c2ad81551aa 208 */
aberk 0:5c2ad81551aa 209 int getRevolutions(void);
aberk 0:5c2ad81551aa 210
aberk 0:5c2ad81551aa 211 private:
aberk 0:5c2ad81551aa 212
aberk 0:5c2ad81551aa 213 /**
aberk 0:5c2ad81551aa 214 * Update the pulse count.
aberk 0:5c2ad81551aa 215 *
aberk 0:5c2ad81551aa 216 * Called on every rising/falling edge of channels A/B.
aberk 0:5c2ad81551aa 217 *
aberk 0:5c2ad81551aa 218 * Reads the state of the channels and determines whether a pulse forward
aberk 0:5c2ad81551aa 219 * or backward has occured, updating the count appropriately.
aberk 0:5c2ad81551aa 220 */
aberk 0:5c2ad81551aa 221 void encode(void);
aberk 0:5c2ad81551aa 222
aberk 0:5c2ad81551aa 223 /**
aberk 0:5c2ad81551aa 224 * Called on every rising edge of channel index to update revolution
aberk 0:5c2ad81551aa 225 * count by one.
aberk 0:5c2ad81551aa 226 */
aberk 0:5c2ad81551aa 227 void index(void);
aberk 0:5c2ad81551aa 228
aberk 0:5c2ad81551aa 229 Encoding encoding_;
aberk 0:5c2ad81551aa 230
aberk 0:5c2ad81551aa 231 InterruptIn channelA_;
aberk 0:5c2ad81551aa 232 InterruptIn channelB_;
aberk 0:5c2ad81551aa 233 InterruptIn index_;
aberk 0:5c2ad81551aa 234
aberk 0:5c2ad81551aa 235 int pulsesPerRev_;
aberk 0:5c2ad81551aa 236 int prevState_;
aberk 0:5c2ad81551aa 237 int currState_;
aberk 0:5c2ad81551aa 238
aberk 0:5c2ad81551aa 239 volatile int pulses_;
aberk 0:5c2ad81551aa 240 volatile int revolutions_;
aberk 0:5c2ad81551aa 241
aberk 0:5c2ad81551aa 242 };
aberk 0:5c2ad81551aa 243
aberk 0:5c2ad81551aa 244 #endif /* QEI_H */