target/avr/asuro_avr_irrc5.c

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/** @file 
 * 
 * AVR implementation of IR-RC5 decoding. Based on the c't-Bot version created 
 * by Benjamin Benz (bbe@heise.de).
 * 
 * @author Denis Martin
 * 
 * This program is free software; you can redistribute it and/or modify it under
 * the terms of the GNU General Public License as published by the Free Software
 * Foundation; either version 2 of the License, or (at your option) any later
 * version.
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
 * details. You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software Foundation, Inc.,
 * 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
 */

#include "asuro.h"

#define AS_IR_SAMPLES_PER_BIT       8   ///< 8 samples per bit
#define AS_IR_SAMPLES_PER_BIT_EARLY 6   ///< edge not before the 6th sample
#define AS_IR_SAMPLES_PER_BIT_LATE  10  ///< edge after 10 samples at the latest

/** 
 * The start bit is only valid after 200 samples with unchanged edge. 
 * According to Benz, this should be 50x1.778ms, but since we have an 8-bit
 * counter for the samples, we are satisfied with about the half of it.
 */
#define AS_IR_PAUSE_SAMPLES         200 

#define AS_IR_PORT  PORTD   ///< port D
#define AS_IR_DDR   DDRD    ///< IO direction port D
#define AS_IR_PINR  PIND    ///< input port D
#define AS_IR_PIN   PD0     ///< IO pin on port D

volatile unsigned short AS_ir_data = 0; ///< last completely read RC5 packet

/** @name private variables to the ISR */
//@{
char AS_ir_lastsample = 0;          ///< last read sample
unsigned char AS_ir_bittimer = 0;   ///< call counter for AS_isr_irrc5()
unsigned short AS_ir_data_tmp = 0;  ///< RC5 bit stream
char AS_ir_bitcount = 0;            ///< number of read bits
//@}

/**
 * ISR for receiving IR-RC5 commands
 * 
 * called about every 222.2us
 */
void AS_isr_irrc5(void) {
    // read a sample
    char sample = 1;
    if (AS_IRRX_SAMPLE) sample = 0;

    // increase bittimer - the timer stops at 255
    if (AS_ir_bittimer < 255) AS_ir_bittimer++;

    if (AS_ir_lastsample != sample) {
        // edge detected
        // start bit?
        if (AS_ir_bitcount == 0) {
            if (sample && (AS_ir_bittimer > AS_IR_PAUSE_SAMPLES) ) {
                // save start bit
                AS_ir_data_tmp = 1;
                AS_ir_bitcount++;

            } else {
                // error
                AS_ir_data_tmp = 0;

            }

            // bittimer reset
            AS_ir_bittimer = 0;
            
        // bits 2..14: only consider edges within bits
        } else {
            if (AS_ir_bittimer >= AS_IR_SAMPLES_PER_BIT_EARLY) {
                if (AS_ir_bittimer <= AS_IR_SAMPLES_PER_BIT_LATE){
                    // save bit
                    AS_ir_data_tmp = (AS_ir_data_tmp << 1) | sample;
                    AS_ir_bitcount++;

                } else {
                    // too late, trop packet
                    AS_ir_bitcount = 0;

                }
                
                // bittimer-reset
                AS_ir_bittimer = 0;
            }
        }
        
    } else {
        // no edge within bit time?
        if (AS_ir_bittimer > AS_IR_SAMPLES_PER_BIT_LATE) {
            // 14 bits read?
            if (AS_ir_bitcount == 14) {
                AS_ir_data = AS_ir_data_tmp;
            }
            
            // drop packet
            AS_ir_bitcount = 0;
        }
    }
    
    // save sample in sample buffer
    AS_ir_lastsample = sample;
}

/**
 * Read the last IR-RC5 code received. This will flush the input, thus
 * subsequent calls will return 0 or a new value.
 * 
 * @return Last IR RC5 code received
 */
inline unsigned short AS_Irrc5Read(void) {
    unsigned short rv = AS_ir_data;
    AS_ir_data = 0;
    return rv;
}

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