mit
Diff: QEI.h
- Revision:
- 0:5c2ad81551aa
- Child:
- 1:3e8503217113
--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/QEI.h Thu Sep 02 16:48:55 2010 +0000 @@ -0,0 +1,244 @@ +/** + * @author Aaron Berk + * + * @section LICENSE + * + * Copyright (c) 2010 ARM Limited + * + * Permission is hereby granted, free of charge, to any person obtaining a copy + * of this software and associated documentation files (the "Software"), to deal + * in the Software without restriction, including without limitation the rights + * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell + * copies of the Software, and to permit persons to whom the Software is + * furnished to do so, subject to the following conditions: + * + * The above copyright notice and this permission notice shall be included in + * all copies or substantial portions of the Software. + * + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE + * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, + * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN + * THE SOFTWARE. + * + * @section DESCRIPTION + * + * Quadrature Encoder Interface. + * + * A quadrature encoder consists of two code tracks on a disc which are 90 + * degrees out of phase. It can be used to determine how far a wheel has + * rotated, relative to a known starting position. + * + * Only one code track changes at a time leading to a more robust system than + * a single track, because any jitter around any edge won't cause a state + * change as the other track will remain constant. + * + * Encoders can be a homebrew affair, consisting of infrared emitters/receivers + * and paper code tracks consisting of alternating black and white sections; + * alternatively, complete disk and PCB emitter/receiver encoder systems can + * be bought, but the interface, regardless of implementation is the same. + * + * +-----+ +-----+ +-----+ + * Channel A | ^ | | | | | + * ---+ ^ +-----+ +-----+ +----- + * ^ ^ + * ^ +-----+ +-----+ +-----+ + * Channel B ^ | | | | | | + * ------+ +-----+ +-----+ +----- + * ^ ^ + * ^ ^ + * 90deg + * + * The interface uses X2 encoding by default which calculates the pulse count + * based on reading the current state after each rising and falling edge of + * channel A. + * + * +-----+ +-----+ +-----+ + * Channel A | | | | | | + * ---+ +-----+ +-----+ +----- + * ^ ^ ^ ^ ^ + * ^ +-----+ ^ +-----+ ^ +-----+ + * Channel B ^ | ^ | ^ | ^ | ^ | | + * ------+ ^ +-----+ ^ +-----+ +-- + * ^ ^ ^ ^ ^ + * ^ ^ ^ ^ ^ + * Pulse count 0 1 2 3 4 5 ... + * + * This interface can also use X4 encoding which calculates the pulse count + * based on reading the current state after each rising and falling edge of + * either channel. + * + * +-----+ +-----+ +-----+ + * Channel A | | | | | | + * ---+ +-----+ +-----+ +----- + * ^ ^ ^ ^ ^ + * ^ +-----+ ^ +-----+ ^ +-----+ + * Channel B ^ | ^ | ^ | ^ | ^ | | + * ------+ ^ +-----+ ^ +-----+ +-- + * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ + * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ + * Pulse count 0 1 2 3 4 5 6 7 8 9 ... + * + * It defaults + * + * An optional index channel can be used which determines when a full + * revolution has occured. + * + * If a 4 pules per revolution encoder was used, with X4 encoding, + * the following would be observed. + * + * +-----+ +-----+ +-----+ + * Channel A | | | | | | + * ---+ +-----+ +-----+ +----- + * ^ ^ ^ ^ ^ + * ^ +-----+ ^ +-----+ ^ +-----+ + * Channel B ^ | ^ | ^ | ^ | ^ | | + * ------+ ^ +-----+ ^ +-----+ +-- + * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ + * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ + * ^ ^ ^ +--+ ^ ^ +--+ ^ + * ^ ^ ^ | | ^ ^ | | ^ + * Index ------------+ +--------+ +----------- + * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ + * Pulse count 0 1 2 3 4 5 6 7 8 9 ... + * Rev. count 0 1 2 + * + * Rotational position in degrees can be calculated by: + * + * (pulse count / X * N) * 360 + * + * Where X is the encoding type [e.g. X4 encoding => X=4], and N is the number + * of pulses per revolution. + * + * Linear position can be calculated by: + * + * (pulse count / X * N) * (1 / PPI) + * + * Where X is encoding type [e.g. X4 encoding => X=44], N is the number of + * pulses per revolution, and PPI is pulses per inch, or the equivalent for + * any other unit of displacement. PPI can be calculated by taking the + * circumference of the wheel or encoder disk and dividing it by the number + * of pulses per revolution. + */ + +#ifndef QEI_H +#define QEI_H + +/** + * Includes + */ +#include "mbed.h" + +/** + * Defines + */ +#define PREV_MASK 0x1 //Mask for the previous state in determining direction +//of rotation. +#define CURR_MASK 0x2 //Mask for the current state in determining direction +//of rotation. +#define INVALID 0x3 //XORing two states where both bits have changed. + +/** + * Quadrature Encoder Interface. + */ +class QEI { + +public: + + typedef enum Encoding { + + X2_ENCODING, + X4_ENCODING + + } Encoding; + + /** + * Constructor. + * + * Reads the current values on channel A and channel B to determine the + * initial state. + * + * Attaches the encode function to the rise/fall interrupt edges of + * channels A and B to perform X4 encoding. + * + * Attaches the index function to the rise interrupt edge of channel index + * (if it is used) to count revolutions. + * + * @param channelA mbed pin for channel A input. + * @param channelB mbed pin for channel B input. + * @param index mbed pin for optional index channel input, + * (pass NC if not needed). + * @param pulsesPerRev Number of pulses in one revolution. + * @param encoding The encoding to use. Uses X2 encoding by default. X2 + * encoding uses interrupts on the rising and falling edges + * of only channel A where as X4 uses them on both + * channels. + */ + QEI(PinName channelA, PinName channelB, PinName index, int pulsesPerRev, Encoding encoding = X2_ENCODING); + + /** + * Reset the encoder. + * + * Sets the pulses and revolutions count to zero. + */ + void reset(void); + + /** + * Read the state of the encoder. + * + * @return The current state of the encoder as a 2-bit number, where: + * bit 1 = The reading from channel B + * bit 2 = The reading from channel A + */ + int getCurrentState(void); + + /** + * Read the number of pulses recorded by the encoder. + * + * @return Number of pulses which have occured. + */ + int getPulses(void); + + /** + * Read the number of revolutions recorded by the encoder on the index channel. + * + * @return Number of revolutions which have occured on the index channel. + */ + int getRevolutions(void); + +private: + + /** + * Update the pulse count. + * + * Called on every rising/falling edge of channels A/B. + * + * Reads the state of the channels and determines whether a pulse forward + * or backward has occured, updating the count appropriately. + */ + void encode(void); + + /** + * Called on every rising edge of channel index to update revolution + * count by one. + */ + void index(void); + + Encoding encoding_; + + InterruptIn channelA_; + InterruptIn channelB_; + InterruptIn index_; + + int pulsesPerRev_; + int prevState_; + int currState_; + + volatile int pulses_; + volatile int revolutions_; + +}; + +#endif /* QEI_H */