adc.c

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 *
 *   Copyright (c) 2012 PX4 Development Team. All rights reserved.
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/**
 * @file adc.c
 *
 * Simple ADC support for PX4IO on STM32.
 */
#include <px4_platform_common/px4_config.h>
#include <stdint.h>

#include <nuttx/arch.h>
#include <arch/stm32/chip.h>
#include <stm32.h>

#include <drivers/drv_hrt.h>
#include <perf/perf_counter.h>

#define DEBUG
#include "px4io.h"

/*
 * Register accessors.
 * For now, no reason not to just use ADC1.
 */
#define REG(_reg)   (*(volatile uint32_t *)(STM32_ADC1_BASE + _reg))

#define rSR     REG(STM32_ADC_SR_OFFSET)
#define rCR1        REG(STM32_ADC_CR1_OFFSET)
#define rCR2        REG(STM32_ADC_CR2_OFFSET)
#define rSMPR1      REG(STM32_ADC_SMPR1_OFFSET)
#define rSMPR2      REG(STM32_ADC_SMPR2_OFFSET)
#define rJOFR1      REG(STM32_ADC_JOFR1_OFFSET)
#define rJOFR2      REG(STM32_ADC_JOFR2_OFFSET)
#define rJOFR3      REG(STM32_ADC_JOFR3_OFFSET)
#define rJOFR4      REG(STM32_ADC_JOFR4_OFFSET)
#define rHTR        REG(STM32_ADC_HTR_OFFSET)
#define rLTR        REG(STM32_ADC_LTR_OFFSET)
#define rSQR1       REG(STM32_ADC_SQR1_OFFSET)
#define rSQR2       REG(STM32_ADC_SQR2_OFFSET)
#define rSQR3       REG(STM32_ADC_SQR3_OFFSET)
#define rJSQR       REG(STM32_ADC_JSQR_OFFSET)
#define rJDR1       REG(STM32_ADC_JDR1_OFFSET)
#define rJDR2       REG(STM32_ADC_JDR2_OFFSET)
#define rJDR3       REG(STM32_ADC_JDR3_OFFSET)
#define rJDR4       REG(STM32_ADC_JDR4_OFFSET)
#define rDR     REG(STM32_ADC_DR_OFFSET)

perf_counter_t      adc_perf;

int
adc_init(void)
{
    adc_perf = perf_alloc(PC_ELAPSED, "adc");

    /* put the ADC into power-down mode */
    rCR2 &= ~ADC_CR2_ADON;
    up_udelay(10);

    /* bring the ADC out of power-down mode */
    rCR2 |= ADC_CR2_ADON;
    up_udelay(10);

    /* do calibration if supported */
#ifdef ADC_CR2_CAL
    rCR2 |= ADC_CR2_RSTCAL;
    up_udelay(1);

    if (rCR2 & ADC_CR2_RSTCAL) {
        return -1;
    }

    rCR2 |= ADC_CR2_CAL;
    up_udelay(100);

    if (rCR2 & ADC_CR2_CAL) {
        return -1;
    }

#endif

    /*
     * Configure sampling time.
     *
     * For electrical protection reasons, we want to be able to have
     * 10K in series with ADC inputs that leave the board. At 12MHz this
     * means we need 28.5 cycles of sampling time (per table 43 in the
     * datasheet).
     */
    rSMPR1 = 0b00000000011011011011011011011011;
    rSMPR2 = 0b00011011011011011011011011011011;

    rCR2 |= ADC_CR2_TSVREFE;        /* enable the temperature sensor / Vrefint channel */

    /* configure for a single-channel sequence */
    rSQR1 = 0;
    rSQR2 = 0;
    rSQR3 = 0;  /* will be updated with the channel at conversion time */

    return 0;
}

/*
  return one measurement, or 0xffff on error
 */
uint16_t
adc_measure(unsigned channel)
{

    perf_begin(adc_perf);

    /* clear any previous EOC */
    rSR = 0;
    (void)rDR;

    /* run a single conversion right now - should take about 60 cycles (a few microseconds) max */
    rSQR3 = channel;
    rCR2 |= ADC_CR2_ADON;

    /* wait for the conversion to complete */
    hrt_abstime now = hrt_absolute_time();

    while (!(rSR & ADC_SR_EOC)) {

        /* never spin forever - this will give a bogus result though */
        if (hrt_elapsed_time(&now) > 100) {
            perf_end(adc_perf);
            return 0xffff;
        }
    }

    /* read the result and clear EOC */
    uint16_t result = rDR;
    rSR = 0;

    perf_end(adc_perf);
    return result;
}