adc.c

00001 /*
00002  * Copyright (c) 2010, University of Colombo School of Computing
00003  * All rights reserved.
00004  *
00005  * Redistribution and use in source and binary forms, with or without
00006  * modification, are permitted provided that the following conditions
00007  * are met:
00008  * 1. Redistributions of source code must retain the above copyright
00009  *    notice, this list of conditions and the following disclaimer.
00010  * 2. Redistributions in binary form must reproduce the above copyright
00011  *    notice, this list of conditions and the following disclaimer in the
00012  *    documentation and/or other materials provided with the distribution.
00013  * 3. Neither the name of the Institute nor the names of its contributors
00014  *    may be used to endorse or promote products derived from this software
00015  *    without specific prior written permission.
00016  *
00017  * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
00018  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
00019  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
00020  * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
00021  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
00022  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
00023  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
00024  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
00025  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
00026  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
00027  * SUCH DAMAGE.
00028  *
00029  * This file is part of the Contiki operating system.
00030  *
00031  */
00032 
00033 #include <avr/io.h>
00034 #include "dev/adc.h"
00035 
00036 /*---------------------------------------------------------------------------*/
00037 void 
00038 adc_init()
00039 {
00040   ADMUX = 0;
00041   /* AVCC with external capacitor at AREF pin. */
00042   ADMUX |= _BV(REFS0);
00043   /* Disable ADC interrupts. */   
00044   ADCSRA &= ~( _BV(ADIE) | _BV(ADIF) );
00045   /* Set ADC prescaler to 64 and clear interrupt flag. */
00046   ADCSRA |= _BV(ADPS2) | _BV(ADPS1) | _BV(ADIE);
00047   
00048 }
00049 /*---------------------------------------------------------------------------*/
00050 /* Poll based approach. The interrupt based adc is currently not used.
00051    The ADC result is right adjusted. First 8 bits(from left) are in ADCL and
00052    other two bits are in ADCH. See Atmega128 datasheet page 228. */
00053 uint16_t 
00054 get_adc(int channel)
00055 {
00056   uint16_t reading;
00057 
00058   ADMUX |= (channel & 0x1F);
00059 
00060   /* Disable ADC interrupts. */
00061   ADCSRA &= ~_BV(ADIE);
00062   /* Clear previous interrupts. */
00063   ADCSRA |= _BV(ADIF);
00064   /* Enable ADC and start conversion. */
00065   ADCSRA |= _BV(ADEN) | _BV(ADSC);
00066   /* Wait until conversion is completed. */
00067   while ( ADCSRA & _BV(ADSC) );
00068   /* Get first 8 bits.  */
00069   reading = ADCL;
00070   /* Get last two bits. */
00071   reading |= (ADCH & 3) << 8;
00072   /* Disable ADC. */
00073   ADCSRA &= ~_BV(ADEN);
00074   return reading;
00075 }
00076 /*---------------------------------------------------------------------------*/

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