NO.18 ADC的基本概念

　　ADC，就是模拟量转换成数字量的一种器件，一种将自然界连续的信号转化成离散的电信号发送给设备。

　　在MSP432中，自带ADC14，一个14位的ADC，好像按照官方的说法这个ADC的速度比MSP430的速度快10倍。

　　具体ADC的内容数电书上都有，什么并联比较型啊，逐次逼近型啊之类，上网百度一下就有。

　　关于我们在MSP432中如何使用这个ADC呢，TIDrivers里有非常强大的库我们可以直接使用。

　　

　　首先我们要了解几个概念：量程\分辨率\采样速率。调用十分简单

/*
 *  ======== adcsinglechannel.c ========
 */
#include <stdint.h>
#include <stddef.h>

/* POSIX Header files */
#include <pthread.h>

/* Driver Header files */
#include <ti/drivers/ADC.h>
#include <ti/display/Display.h>

/* Driver configuration */
#include "ti_drivers_config.h"

/* ADC sample count */
#define ADC_SAMPLE_COUNT  (10)

#define THREADSTACKSIZE   (768)

/* ADC conversion result variables */
uint16_t adcValue0;
uint32_t adcValue0MicroVolt;
uint16_t adcValue1[ADC_SAMPLE_COUNT];
uint32_t adcValue1MicroVolt[ADC_SAMPLE_COUNT];

static Display_Handle display;

/*
 *  ======== threadFxn0 ========
 *  Open an ADC instance and get a sampling result from a one-shot conversion.
 */
void *threadFxn0(void *arg0)
{
    ADC_Handle   adc;
    ADC_Params   params;
    int_fast16_t res;

    ADC_Params_init(&params);
    adc = ADC_open(CONFIG_ADC_0, &params);

    if (adc == NULL) {
        Display_printf(display, 0, 0, "Error initializing ADC0\n");
        while (1);
    }

    /* Blocking mode conversion */
    res = ADC_convert(adc, &adcValue0);

    if (res == ADC_STATUS_SUCCESS) {

        adcValue0MicroVolt = ADC_convertRawToMicroVolts(adc, adcValue0);

        Display_printf(display, 0, 0, "ADC0 raw result: %d\n", adcValue0);
        Display_printf(display, 0, 0, "ADC0 convert result: %d uV\n",
            adcValue0MicroVolt);
    }
    else {
        Display_printf(display, 0, 0, "ADC0 convert failed\n");
    }

    ADC_close(adc);

    return (NULL);
}

/*
 *  ======== threadFxn1 ========
 *  Open a ADC handle and get an array of sampling results after
 *  calling several conversions.
 */
void *threadFxn1(void *arg0)
{
    uint16_t     i;
    ADC_Handle   adc;
    ADC_Params   params;
    int_fast16_t res;

    ADC_Params_init(&params);
    adc = ADC_open(CONFIG_ADC_1, &params);

    if (adc == NULL) {
        Display_printf(display, 0, 0, "Error initializing ADC1\n");
        while (1);
    }

    for (i = 0; i < ADC_SAMPLE_COUNT; i++) {
        res = ADC_convert(adc, &adcValue1[i]);

        if (res == ADC_STATUS_SUCCESS) {

            adcValue1MicroVolt[i] = ADC_convertRawToMicroVolts(adc, adcValue1[i]);

            Display_printf(display, 0, 0, "ADC1 raw result (%d): %d\n", i,
                           adcValue1[i]);
            Display_printf(display, 0, 0, "ADC1 convert result (%d): %d uV\n", i,
                adcValue1MicroVolt[i]);
        }
        else {
            Display_printf(display, 0, 0, "ADC1 convert failed (%d)\n", i);
        }
    }

    ADC_close(adc);

    return (NULL);
}

/*
 *  ======== mainThread ========
 */
void *mainThread(void *arg0)
{
    pthread_t           thread0, thread1;
    pthread_attr_t      attrs;
    struct sched_param  priParam;
    int                 retc;
    int                 detachState;

    /* Call driver init functions */
    ADC_init();
    Display_init();

    /* Open the display for output */
    display = Display_open(Display_Type_UART, NULL);
    if (display == NULL) {
        /* Failed to open display driver */
        while (1);
    }

    Display_printf(display, 0, 0, "Starting the acdsinglechannel example\n");

    /* Create application threads */
    pthread_attr_init(&attrs);

    detachState = PTHREAD_CREATE_DETACHED;
    /* Set priority and stack size attributes */
    retc = pthread_attr_setdetachstate(&attrs, detachState);
    if (retc != 0) {
        /* pthread_attr_setdetachstate() failed */
        while (1);
    }

    retc |= pthread_attr_setstacksize(&attrs, THREADSTACKSIZE);
    if (retc != 0) {
        /* pthread_attr_setstacksize() failed */
        while (1);
    }

    /* Create threadFxn0 thread */
    priParam.sched_priority = 1;
    pthread_attr_setschedparam(&attrs, &priParam);

    retc = pthread_create(&thread0, &attrs, threadFxn0, NULL);
    if (retc != 0) {
        /* pthread_create() failed */
        while (1);
    }

    /* Create threadFxn1 thread */
    retc = pthread_create(&thread1, &attrs, threadFxn1, (void* )0);
    if (retc != 0) {
        /* pthread_create() failed */
        while (1);
    }

    return (NULL);
}