diff -r 86f099bda525 -r 8f2be7aaec00 lib/QEI/QEI.cpp --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/lib/QEI/QEI.cpp Thu Oct 15 01:12:31 2020 +0200 @@ -0,0 +1,296 @@ +/** + * @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. + */ + +/** + * Includes + */ +#include "QEI.h" + +QEI::QEI(PinName channelA, + PinName channelB, + PinName index, + int pulsesPerRev, + Encoding encoding, + const event_callback_t& ev_callback) : + channelA_(channelA), + channelB_(channelB), + index_(index), + _callback(ev_callback) { + + pulses_ = 0; + revolutions_ = 0; + pulsesPerRev_ = pulsesPerRev; + encoding_ = encoding; + + //Workout what the current state is. + int chanA = channelA_.read(); + int chanB = channelB_.read(); + + //2-bit state. + currState_ = (chanA << 1) | (chanB); + prevState_ = currState_; + + //X2 encoding uses interrupts on only channel A. + //X4 encoding uses interrupts on channel A, + //and on channel B. + channelA_.rise(callback(this, &QEI::encode)); + channelA_.fall(callback(this, &QEI::encode)); + + //If we're using X4 encoding, then attach interrupts to channel B too. + if (encoding == X4_ENCODING) { + channelB_.rise(callback(this, &QEI::encode)); + channelB_.fall(callback(this, &QEI::encode)); + } + //Index is optional. + if (index_ != NC) { + index_.rise(callback(this, &QEI::index)); + } + +} + +void QEI::reset(void) { + + pulses_ = 0; + revolutions_ = 0; + +} + +int QEI::getCurrentState(void) { + + return currState_; + +} + +int QEI::getPulses(void) { + + return pulses_; + +} + +int QEI::getRevolutions(void) { + + return revolutions_; + +} + +// +-------------+ +// | X2 Encoding | +// +-------------+ +// +// When observing states two patterns will appear: +// +// Counter clockwise rotation: +// +// 10 -> 01 -> 10 -> 01 -> ... +// +// Clockwise rotation: +// +// 11 -> 00 -> 11 -> 00 -> ... +// +// We consider counter clockwise rotation to be "forward" and +// counter clockwise to be "backward". Therefore pulse count will increase +// during counter clockwise rotation and decrease during clockwise rotation. +// +// +-------------+ +// | X4 Encoding | +// +-------------+ +// +// There are four possible states for a quadrature encoder which correspond to +// 2-bit gray code. +// +// A state change is only valid if of only one bit has changed. +// A state change is invalid if both bits have changed. +// +// Clockwise Rotation -> +// +// 00 01 11 10 00 +// +// <- Counter Clockwise Rotation +// +// If we observe any valid state changes going from left to right, we have +// moved one pulse clockwise [we will consider this "backward" or "negative"]. +// +// If we observe any valid state changes going from right to left we have +// moved one pulse counter clockwise [we will consider this "forward" or +// "positive"]. +// +// We might enter an invalid state for a number of reasons which are hard to +// predict - if this is the case, it is generally safe to ignore it, update +// the state and carry on, with the error correcting itself shortly after. +void QEI::encode(void) { + + int change = 0; + int chanA = channelA_.read(); + int chanB = channelB_.read(); + + //2-bit state. + currState_ = (chanA << 1) | (chanB); + + if (encoding_ == X2_ENCODING) { + + //11->00->11->00 is counter clockwise rotation or "forward". + if ((prevState_ == 0x3 && currState_ == 0x0) || + (prevState_ == 0x0 && currState_ == 0x3)) { + change = 1; + pulses_++; + + } + //10->01->10->01 is clockwise rotation or "backward". + else if ((prevState_ == 0x2 && currState_ == 0x1) || + (prevState_ == 0x1 && currState_ == 0x2)) { + change = -1; + pulses_--; + + } + + } else if (encoding_ == X4_ENCODING) { + + //Entered a new valid state. + if (((currState_ ^ prevState_) != INVALID) && (currState_ != prevState_)) { + //2 bit state. Right hand bit of prev XOR left hand bit of current + //gives 0 if clockwise rotation and 1 if counter clockwise rotation. + change = (prevState_ & PREV_MASK) ^ ((currState_ & CURR_MASK) >> 1); + + if (change == 0) { + change = -1; + } + + pulses_ -= change; + } + + } + + if (_callback && (change != 0)) + _callback.call(change==1?1:0); + + prevState_ = currState_; + +} + +void QEI::index(void) { + + revolutions_++; + +}