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/encoder.h

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/*! \file encoder.h \brief Quadrature Encoder reader/driver. */
//*****************************************************************************
//
// File Name    : 'encoder.h'
// Title        : Quadrature Encoder reader/driver
// Author       : Pascal Stang - Copyright (C) 2003
// Created      : 2003.01.26
// Revised      : 2003.02.24
// Version      : 0.3
// Target MCU   : Atmel AVR Series
// Editor Tabs  : 4
//
// Description  : This library allows easy interfacing of quadrature encoders
//      to the Atmel AVR-series processors.
//
//      Quadrature encoders have two digital outputs usually called PhaseA and
//  PhaseB.  When the encoder rotates, PhaseA and PhaseB produce square wave
//  pulses where each pulse represents a fraction of a turn of the encoder
//  shaft.  Encoders are rated for a certain number of pulses (or counts) per
//  complete revolution of the shaft.  Common counts/revolution specs are 50,
//  100,128,200,250,256,500,etc.  By counting the number of pulses output on
//  one of the phases starting from time0, you can calculate the total
//  rotational distance the encoder has traveled.
//  
//  Often, however, we want current position not just total distance traveled.
//  For this it is necessary to know not only how far the encoder has traveled,
//  but also which direction it was going at each step of the way.  To do this
//  we need to use both outputs (or phases) of the quadrature encoder.
//
//  The pulses from PhaseA and PhaseB on quadrature encoders are always aligned
//  90 degrees out-of-phase (otherwise said: 1/4 wavelength apart).  This
//  special phase relationship lets us extract both the distance and direction
//  the encoder has rotated from the outputs.
//
//  To do this, consider Phase A to be the distance counter.  On each rising
//  edge of PhaseA we will count 1 "tic" of distance, but we need to know the
//  direction.  Look at the quadrature waveform plot below.  Notice that when
//  we travel forward in time (left->right), PhaseB is always low (logic 0) at
//  the rising edge of PhaseA.  When we travel backwards in time (right->left),
//  PhaseB is always high (logic 1) at the rising edge of PhaseA.  Note that
//  traveling forward or backwards in time is the same thing as rotating
//  forwards or bardwards. Thus, if PhaseA is our counter, PhaseB indicates
//  direction.
//
//  Here is an example waveform from a quadrature encoder:
//
//                /---\   /---\   /---\   /---\   /---\   /---\
//  Phase A:      |   |   |   |   |   |   |   |   |   |   |   |
//             ---/   \---/   \---/   \---/   \---/   \---/   \-
//             -\   /---\   /---\   /---\   /---\   /---\   /---
//  Phase B:    |   |   |   |   |   |   |   |   |   |   |   |
//              \---/   \---/   \---/   \---/   \---/   \---/
//  Time:    <--------------------------------------------------->
//  Rotate FWD: >----------------------------------------------> 
//  Rotate REV: <----------------------------------------------<
//
//  To keep track of the encoder position in software, we connect PhaseA to an
//  external processor interrupt line, and PhaseB to any I/O pin.  We set up
//  the external interrupt to trigger whenever PhaseA produces a rising edge.
//  When a rising edge is detected, our interrupt handler function is executed.
//  Inside the handler function, we quickly check the PhaseB line to see if it
//  is high or low.  If it is high, we increment the encoder's position
//  counter, otherwise we decrement it.  The encoder position counter can be
//  read at any time to find out the current position.
//
//
// NOTE: This code is currently below version 1.0, and therefore is considered
// to be lacking in some functionality or documentation, or may not be fully
// tested.  Nonetheless, you can expect most functions to work.
//
// This code is distributed under the GNU Public License
//      which can be found at http://www.gnu.org/licenses/gpl.txt
//
//*****************************************************************************

#ifndef ENCODER_H
#define ENCODER_H

#include "global.h"

// include encoder configuration file
#include "encoderconf.h"

// constants/macros/typdefs

// defines for processor compatibility
// chose proper Interrupt Mask (IMSK)
#ifdef EIMSK
    #define IMSK    EIMSK   // for processors mega128, mega64
#else
    #define IMSK    GIMSK   // for other processors 90s8515, mega163, etc
#endif


//! Encoder state structure
//   stores the position and other information from each encoder
typedef struct struct_EncoderState
{   
    s32 position;       ///< position
//  s32 velocity;       ///< velocity
} EncoderStateType;


// functions

//! encoderInit() initializes hardware and encoder position readings
//      Run this init routine once before using any other encoder function.
void encoderInit(void);

//! encoderOff() disables hardware and stops encoder position updates
void encoderOff(void);

//! encoderGetPosition() reads the current position of the encoder 
s32 encoderGetPosition(u08 encoderNum);

//! encoderSetPosition() sets the current position of the encoder
void encoderSetPosition(u08 encoderNum, s32 position);

#endif

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