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QEI.h
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/**
* @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 = X4_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.
*/
float getRevolutions(void);
float getDistance(float diameter);
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_;
float pulsesPerRev_;
int prevState_;
int currState_;
volatile int pulses_;
volatile int revolutions_;
};
#endif /* QEI_H */