Minor test serial map
Diff: QEI.cpp
- Revision:
- 1:e567b2f1aebf
- Parent:
- 0:5c2ad81551aa
--- a/QEI.cpp Thu Sep 02 16:48:55 2010 +0000 +++ /dev/null Thu Jan 01 00:00:00 1970 +0000 @@ -1,289 +0,0 @@ -/** - * @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) : channelA_(channelA), channelB_(channelB), - index_(index) { - - 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(this, &QEI::encode); - channelA_.fall(this, &QEI::encode); - - //If we're using X4 encoding, then attach interrupts to channel B too. - if (encoding == X4_ENCODING) { - channelB_.rise(this, &QEI::encode); - channelB_.fall(this, &QEI::encode); - } - //Index is optional. - if (index != NC) { - index_.rise(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)) { - - pulses_++; - - } - //10->01->10->01 is clockwise rotation or "backward". - else if ((prevState_ == 0x2 && currState_ == 0x1) || - (prevState_ == 0x1 && currState_ == 0x2)) { - - 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; - } - - } - - prevState_ = currState_; - -} - -void QEI::index(void) { - - revolutions_++; - -}