contiki/platform/iris/dev/adc.c
2011-07-15 16:36:24 +09:00

77 lines
2.9 KiB
C

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