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77 lines
2.9 KiB
C
77 lines
2.9 KiB
C
/*
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* Copyright (c) 2010, University of Colombo School of Computing
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the Institute nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* This file is part of the Contiki operating system.
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*
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*/
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#include <avr/io.h>
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#include "dev/adc.h"
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/*---------------------------------------------------------------------------*/
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void
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adc_init()
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{
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ADMUX = 0;
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/* AVCC with external capacitor at AREF pin. */
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ADMUX |= _BV(REFS0);
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/* Disable ADC interrupts. */
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ADCSRA &= ~( _BV(ADIE) | _BV(ADIF) );
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/* Set ADC prescaler to 64 and clear interrupt flag. */
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ADCSRA |= _BV(ADPS2) | _BV(ADPS1) | _BV(ADIE);
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}
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/*---------------------------------------------------------------------------*/
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/* Poll based approach. The interrupt based adc is currently not used.
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The ADC result is right adjusted. First 8 bits(from left) are in ADCL and
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other two bits are in ADCH. See Atmega128 datasheet page 228. */
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uint16_t
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get_adc(int channel)
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{
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uint16_t reading;
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ADMUX |= (channel & 0x1F);
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/* Disable ADC interrupts. */
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ADCSRA &= ~_BV(ADIE);
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/* Clear previous interrupts. */
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ADCSRA |= _BV(ADIF);
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/* Enable ADC and start conversion. */
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ADCSRA |= _BV(ADEN) | _BV(ADSC);
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/* Wait until conversion is completed. */
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while ( ADCSRA & _BV(ADSC) );
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/* Get first 8 bits. */
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reading = ADCL;
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/* Get last two bits. */
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reading |= (ADCH & 3) << 8;
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/* Disable ADC. */
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ADCSRA &= ~_BV(ADEN);
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return reading;
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}
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/*---------------------------------------------------------------------------*/
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