如何为嵌入式 C 中的传感器定义引脚？

Question

我有一个北欧nRF52840DK board that needs to be connected to an LSM6DSL accelerometer。我正在使用 Zephyr RTOS，Zephyr 的示例代码如下所示：

/*
 * Copyright (c) 2018 STMicroelectronics
 *
 * SPDX-License-Identifier: Apache-2.0
 */

#include <zephyr.h>
#include <device.h>
#include <drivers/sensor.h>
#include <stdio.h>
#include <sys/util.h>

static inline float out_ev(struct sensor_value *val)
{
    return (val->val1 + (float)val->val2 / 1000000);
}

static int print_samples;
static int lsm6dsl_trig_cnt;

static struct sensor_value accel_x_out, accel_y_out, accel_z_out;
static struct sensor_value gyro_x_out, gyro_y_out, gyro_z_out;
#if defined(CONFIG_LSM6DSL_EXT0_LIS2MDL)
static struct sensor_value magn_x_out, magn_y_out, magn_z_out;
#endif
#if defined(CONFIG_LSM6DSL_EXT0_LPS22HB)
static struct sensor_value press_out, temp_out;
#endif

#ifdef CONFIG_LSM6DSL_TRIGGER
static void lsm6dsl_trigger_handler(const struct device *dev,
                    struct sensor_trigger *trig)
{
    static struct sensor_value accel_x, accel_y, accel_z;
    static struct sensor_value gyro_x, gyro_y, gyro_z;
#if defined(CONFIG_LSM6DSL_EXT0_LIS2MDL)
    static struct sensor_value magn_x, magn_y, magn_z;
#endif
#if defined(CONFIG_LSM6DSL_EXT0_LPS22HB)
    static struct sensor_value press, temp;
#endif
    lsm6dsl_trig_cnt++;

    sensor_sample_fetch_chan(dev, SENSOR_CHAN_ACCEL_XYZ);
    sensor_channel_get(dev, SENSOR_CHAN_ACCEL_X, &accel_x);
    sensor_channel_get(dev, SENSOR_CHAN_ACCEL_Y, &accel_y);
    sensor_channel_get(dev, SENSOR_CHAN_ACCEL_Z, &accel_z);

    /* lsm6dsl gyro */
    sensor_sample_fetch_chan(dev, SENSOR_CHAN_GYRO_XYZ);
    sensor_channel_get(dev, SENSOR_CHAN_GYRO_X, &gyro_x);
    sensor_channel_get(dev, SENSOR_CHAN_GYRO_Y, &gyro_y);
    sensor_channel_get(dev, SENSOR_CHAN_GYRO_Z, &gyro_z);

#if defined(CONFIG_LSM6DSL_EXT0_LIS2MDL)
    /* lsm6dsl external magn */
    sensor_sample_fetch_chan(dev, SENSOR_CHAN_MAGN_XYZ);
    sensor_channel_get(dev, SENSOR_CHAN_MAGN_X, &magn_x);
    sensor_channel_get(dev, SENSOR_CHAN_MAGN_Y, &magn_y);
    sensor_channel_get(dev, SENSOR_CHAN_MAGN_Z, &magn_z);
#endif

#if defined(CONFIG_LSM6DSL_EXT0_LPS22HB)
    /* lsm6dsl external press/temp */
    sensor_sample_fetch_chan(dev, SENSOR_CHAN_PRESS);
    sensor_channel_get(dev, SENSOR_CHAN_PRESS, &press);

    sensor_sample_fetch_chan(dev, SENSOR_CHAN_AMBIENT_TEMP);
    sensor_channel_get(dev, SENSOR_CHAN_AMBIENT_TEMP, &temp);
#endif

    if (print_samples) {
        print_samples = 0;

        accel_x_out = accel_x;
        accel_y_out = accel_y;
        accel_z_out = accel_z;

        gyro_x_out = gyro_x;
        gyro_y_out = gyro_y;
        gyro_z_out = gyro_z;

#if defined(CONFIG_LSM6DSL_EXT0_LIS2MDL)
        magn_x_out = magn_x;
        magn_y_out = magn_y;
        magn_z_out = magn_z;
#endif

#if defined(CONFIG_LSM6DSL_EXT0_LPS22HB)
        press_out = press;
        temp_out = temp;
#endif
    }

}
#endif

void main(void)
{
    int cnt = 0;
    char out_str[64];
    struct sensor_value odr_attr;
    const struct device *lsm6dsl_dev = device_get_binding(DT_LABEL(DT_INST(0, st_lsm6dsl)));

    if (lsm6dsl_dev == NULL) {
        printk("Could not get LSM6DSL device\n");
        return;
    }

    /* set accel/gyro sampling frequency to 104 Hz */
    odr_attr.val1 = 104;
    odr_attr.val2 = 0;

    if (sensor_attr_set(lsm6dsl_dev, SENSOR_CHAN_ACCEL_XYZ,
                SENSOR_ATTR_SAMPLING_FREQUENCY, &odr_attr) < 0) {
        printk("Cannot set sampling frequency for accelerometer.\n");
        return;
    }

    if (sensor_attr_set(lsm6dsl_dev, SENSOR_CHAN_GYRO_XYZ,
                SENSOR_ATTR_SAMPLING_FREQUENCY, &odr_attr) < 0) {
        printk("Cannot set sampling frequency for gyro.\n");
        return;
    }

#ifdef CONFIG_LSM6DSL_TRIGGER
    struct sensor_trigger trig;

    trig.type = SENSOR_TRIG_DATA_READY;
    trig.chan = SENSOR_CHAN_ACCEL_XYZ;

    if (sensor_trigger_set(lsm6dsl_dev, &trig, lsm6dsl_trigger_handler) != 0) {
        printk("Could not set sensor type and channel\n");
        return;
    }
#endif

    if (sensor_sample_fetch(lsm6dsl_dev) < 0) {
        printk("Sensor sample update error\n");
        return;
    }

    while (1) {
        /* Erase previous */
        printk("[=10=]334");
        printf("LSM6DSL sensor samples:\n\n");

        /* lsm6dsl accel */
        sprintf(out_str, "accel x:%f ms/2 y:%f ms/2 z:%f ms/2",
                              out_ev(&accel_x_out),
                              out_ev(&accel_y_out),
                              out_ev(&accel_z_out));
        printk("%s\n", out_str);

        /* lsm6dsl gyro */
        sprintf(out_str, "gyro x:%f dps y:%f dps z:%f dps",
                               out_ev(&gyro_x_out),
                               out_ev(&gyro_y_out),
                               out_ev(&gyro_z_out));
        printk("%s\n", out_str);

#if defined(CONFIG_LSM6DSL_EXT0_LIS2MDL)
        /* lsm6dsl external magn */
        sprintf(out_str, "magn x:%f gauss y:%f gauss z:%f gauss",
                               out_ev(&magn_x_out),
                               out_ev(&magn_y_out),
                               out_ev(&magn_z_out));
        printk("%s\n", out_str);
#endif

#if defined(CONFIG_LSM6DSL_EXT0_LPS22HB)
        /* lsm6dsl external press/temp */
        sprintf(out_str, "press: %f kPa - temp: %f deg",
            out_ev(&press_out), out_ev(&temp_out));
        printk("%s\n", out_str);
#endif

        printk("loop:%d trig_cnt:%d\n\n", ++cnt, lsm6dsl_trig_cnt);

        print_samples = 1;
        k_sleep(K_MSEC(2000));
    }
}

根据我以前使用Arduino的经验，你需要在main函数之前定义管脚，但是在这个代码示例中没有任何关于管脚的定义。所以我的问题是：电路板如何知道在连接到传感器时使用哪些引脚？

提前致谢！

Answer 1

在嵌入式 C（裸机和一些 RTOS）中，开发人员应该知道什么连接在哪里以及使用哪些寄存器通过驱动正确的引脚来访问连接的硬件。

在 Zephyr 的特定情况下（以及 Das U-Boot and Linux on some architectures), the system configuration (among other things pins, but not only) is described by a device-tree。它是一种“用于描述硬件的数据结构”，它允许固件代码独立于实际硬件。

设备树会描述很多东西，最重要的是：

设备的内存映射
CPU 列表及其属性（频率、缓存...）
外围设备及其配置

Zephyr 确实有一个 very good introduction to device-tree。

在您发布的代码中，Zephyr 在执行以下行时确实从设备树中检索了设备信息：

const struct device *lsm6dsl_dev = device_get_binding(DT_LABEL(DT_INST(0, st_lsm6dsl)));

如何为嵌入式 C 中的传感器定义引脚？

How are pins defined for sensors in embedded C?

c

embedded

zephyr-rtos