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comparison: lib/QEI/QEI.h

lib/QEI/QEI.h

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1 /**
2 * @author Aaron Berk
3 *
4 * @section LICENSE
5 *
6 * Copyright (c) 2010 ARM Limited
7 *
8 * Permission is hereby granted, free of charge, to any person obtaining a copy
9 * of this software and associated documentation files (the "Software"), to deal
10 * in the Software without restriction, including without limitation the rights
11 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
12 * copies of the Software, and to permit persons to whom the Software is
13 * furnished to do so, subject to the following conditions:
14 *
15 * The above copyright notice and this permission notice shall be included in
16 * all copies or substantial portions of the Software.
17 *
18 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
19 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
20 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
21 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
22 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
23 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
24 * THE SOFTWARE.
25 *
26 * @section DESCRIPTION
27 *
28 * Quadrature Encoder Interface.
29 *
30 * A quadrature encoder consists of two code tracks on a disc which are 90
31 * degrees out of phase. It can be used to determine how far a wheel has
32 * rotated, relative to a known starting position.
33 *
34 * Only one code track changes at a time leading to a more robust system than
35 * a single track, because any jitter around any edge won't cause a state
36 * change as the other track will remain constant.
37 *
38 * Encoders can be a homebrew affair, consisting of infrared emitters/receivers
39 * and paper code tracks consisting of alternating black and white sections;
40 * alternatively, complete disk and PCB emitter/receiver encoder systems can
41 * be bought, but the interface, regardless of implementation is the same.
42 *
43 * +-----+ +-----+ +-----+
44 * Channel A | ^ | | | | |
45 * ---+ ^ +-----+ +-----+ +-----
46 * ^ ^
47 * ^ +-----+ +-----+ +-----+
48 * Channel B ^ | | | | | |
49 * ------+ +-----+ +-----+ +-----
50 * ^ ^
51 * ^ ^
52 * 90deg
53 *
54 * The interface uses X2 encoding by default which calculates the pulse count
55 * based on reading the current state after each rising and falling edge of
56 * channel A.
57 *
58 * +-----+ +-----+ +-----+
59 * Channel A | | | | | |
60 * ---+ +-----+ +-----+ +-----
61 * ^ ^ ^ ^ ^
62 * ^ +-----+ ^ +-----+ ^ +-----+
63 * Channel B ^ | ^ | ^ | ^ | ^ | |
64 * ------+ ^ +-----+ ^ +-----+ +--
65 * ^ ^ ^ ^ ^
66 * ^ ^ ^ ^ ^
67 * Pulse count 0 1 2 3 4 5 ...
68 *
69 * This interface can also use X4 encoding which calculates the pulse count
70 * based on reading the current state after each rising and falling edge of
71 * either channel.
72 *
73 * +-----+ +-----+ +-----+
74 * Channel A | | | | | |
75 * ---+ +-----+ +-----+ +-----
76 * ^ ^ ^ ^ ^
77 * ^ +-----+ ^ +-----+ ^ +-----+
78 * Channel B ^ | ^ | ^ | ^ | ^ | |
79 * ------+ ^ +-----+ ^ +-----+ +--
80 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
81 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
82 * Pulse count 0 1 2 3 4 5 6 7 8 9 ...
83 *
84 * It defaults
85 *
86 * An optional index channel can be used which determines when a full
87 * revolution has occured.
88 *
89 * If a 4 pules per revolution encoder was used, with X4 encoding,
90 * the following would be observed.
91 *
92 * +-----+ +-----+ +-----+
93 * Channel A | | | | | |
94 * ---+ +-----+ +-----+ +-----
95 * ^ ^ ^ ^ ^
96 * ^ +-----+ ^ +-----+ ^ +-----+
97 * Channel B ^ | ^ | ^ | ^ | ^ | |
98 * ------+ ^ +-----+ ^ +-----+ +--
99 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
100 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
101 * ^ ^ ^ +--+ ^ ^ +--+ ^
102 * ^ ^ ^ | | ^ ^ | | ^
103 * Index ------------+ +--------+ +-----------
104 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
105 * Pulse count 0 1 2 3 4 5 6 7 8 9 ...
106 * Rev. count 0 1 2
107 *
108 * Rotational position in degrees can be calculated by:
109 *
110 * (pulse count / X * N) * 360
111 *
112 * Where X is the encoding type [e.g. X4 encoding => X=4], and N is the number
113 * of pulses per revolution.
114 *
115 * Linear position can be calculated by:
116 *
117 * (pulse count / X * N) * (1 / PPI)
118 *
119 * Where X is encoding type [e.g. X4 encoding => X=44], N is the number of
120 * pulses per revolution, and PPI is pulses per inch, or the equivalent for
121 * any other unit of displacement. PPI can be calculated by taking the
122 * circumference of the wheel or encoder disk and dividing it by the number
123 * of pulses per revolution.
124 */
125
126 #ifndef QEI_H
127 #define QEI_H
128
129 /**
130 * Includes
131 */
132 #include "mbed.h"
133
134 /**
135 * Defines
136 */
137 #define PREV_MASK 0x1 //Mask for the previous state in determining direction
138 //of rotation.
139 #define CURR_MASK 0x2 //Mask for the current state in determining direction
140 //of rotation.
141 #define INVALID 0x3 //XORing two states where both bits have changed.
142
143 /**
144 * Quadrature Encoder Interface.
145 */
146 class QEI {
147
148 public:
149
150 typedef enum Encoding {
151
152 X2_ENCODING,
153 X4_ENCODING
154
155 } Encoding;
156
157 /**
158 * Constructor.
159 *
160 * Reads the current values on channel A and channel B to determine the
161 * initial state.
162 *
163 * Attaches the encode function to the rise/fall interrupt edges of
164 * channels A and B to perform X4 encoding.
165 *
166 * Attaches the index function to the rise interrupt edge of channel index
167 * (if it is used) to count revolutions.
168 *
169 * @param channelA mbed pin for channel A input.
170 * @param channelB mbed pin for channel B input.
171 * @param index mbed pin for optional index channel input,
172 * (pass NC if not needed).
173 * @param pulsesPerRev Number of pulses in one revolution.
174 * @param encoding The encoding to use. Uses X2 encoding by default. X2
175 * encoding uses interrupts on the rising and falling edges
176 * of only channel A where as X4 uses them on both
177 * channels.
178 */
179 QEI(PinName channelA, PinName channelB, PinName index,
180 int pulsesPerRev, Encoding encoding = X2_ENCODING,
181 const event_callback_t& ev_callback=NULL);
182
183 /**
184 * Reset the encoder.
185 *
186 * Sets the pulses and revolutions count to zero.
187 */
188 void reset(void);
189
190 /**
191 * Read the state of the encoder.
192 *
193 * @return The current state of the encoder as a 2-bit number, where:
194 * bit 1 = The reading from channel B
195 * bit 2 = The reading from channel A
196 */
197 int getCurrentState(void);
198
199 /**
200 * Read the number of pulses recorded by the encoder.
201 *
202 * @return Number of pulses which have occured.
203 */
204 int getPulses(void);
205
206 /**
207 * Read the number of revolutions recorded by the encoder on the index channel.
208 *
209 * @return Number of revolutions which have occured on the index channel.
210 */
211 int getRevolutions(void);
212
213 void attach(const event_callback_t& callback=NULL) {
214 _callback = callback;
215 };
216
217 private:
218
219 /**
220 * Update the pulse count.
221 *
222 * Called on every rising/falling edge of channels A/B.
223 *
224 * Reads the state of the channels and determines whether a pulse forward
225 * or backward has occured, updating the count appropriately.
226 */
227 void encode(void);
228
229 /**
230 * Called on every rising edge of channel index to update revolution
231 * count by one.
232 */
233 void index(void);
234
235 Encoding encoding_;
236
237 InterruptIn channelA_;
238 InterruptIn channelB_;
239 InterruptIn index_;
240
241 int pulsesPerRev_;
242 int prevState_;
243 int currState_;
244
245 volatile int pulses_;
246 volatile int revolutions_;
247 event_callback_t _callback;
248
249 };
250
251 #endif /* QEI_H */

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