adc.c
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/*
* Copyright (C) 2017 Freie Universität Berlin
*
* This file is subject to the terms and conditions of the GNU Lesser
* General Public License v2.1. See the file LICENSE in the top level
* directory for more details.
*/
/**
* @ingroup cpu_sam3
* @{
*
* @file
* @brief Low-level ADC driver implementation
*
* @author Hauke Petersen <hauke.petersen@fu-berlin.de>
*
* @}
*/
#include <stdio.h>
#include "mutex.h"
#include "periph/adc.h"
#define RES_INVALID (0x0f)
#define WP_KEY (0x414443)
#define PMC_BIT (1 << (ID_ADC - 32))
/* max ADC clock is 6.4MHz, we aim for 5MHz per default */
#ifndef ADC_CLOCK_TARGET
#define ADC_CLOCK_TARGET (5000000)
#endif
#define PRESCALER ((CLOCK_CORECLOCK / (2 * ADC_CLOCK_TARGET)) - 1)
static mutex_t lock = MUTEX_INIT;
static inline void use(void)
{
mutex_lock(&lock);
PMC->PMC_PCER1 = PMC_BIT;
}
static inline void done(void)
{
PMC->PMC_PCDR1 = PMC_BIT;
mutex_unlock(&lock);
}
int adc_init(adc_t line)
{
assert(line < ADC_NUMOF);
use();
/* disable ADC write protection */
ADC->ADC_WPMR = ADC_WPMR_WPKEY(WP_KEY);
ADC->ADC_CHDR = 0x0000ffff;
/* if line 15 is used, enable the temperature sensor */
if (line == 15) {
ADC->ADC_ACR |= ADC_ACR_TSON;
}
done();
return 0;
}
int adc_sample(adc_t line, adc_res_t res)
{
assert(line < ADC_NUMOF);
/* check if resolution is applicable */
if (res & RES_INVALID) {
return -1;
}
use();
/* set resolution */
ADC->ADC_MR = (res | ADC_MR_PRESCAL(PRESCALER));
/* enable channel */
ADC->ADC_CHER = (1 << line);
/* start conversion */
ADC->ADC_CR = ADC_CR_START;
/* wait for result */
while (!(ADC->ADC_ISR & ADC_ISR_DRDY)) {}
/* read result */
int sample = (int)(ADC->ADC_LCDR & ADC_LCDR_LDATA_Msk);
/* disable channel */
ADC->ADC_CHDR = (1 << line);
done();
return sample;
}