【rtthread设备】第六篇：i2c设备

[rtthread设备]系列文章

【rtthread设备】第零篇：IO设备
【rtthread设备】第一篇：pin设备
【rtthread设备】第二篇：rtc设备
【rtthread设备】第三篇：adc设备
【rtthread设备】第五篇：hwtimer设备
【rtthread设备】第六篇：i2c设备
【rtthread设备】第七篇：spi设备
【rtthread设备】第八篇：看门狗设备

一、i2c设备驱动框架

在i2c通信中，mcu一般作为主机与外围的i2c芯片通信，rttread将i2c主机虚拟成i2c总线设备，通过i2c设备接口与从机通信。
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二、i2c驱动api

2.1 常用api

//获得设备句柄
/*
name：i2c总线设备名称
*/
rt_device_t rt_device_find(const char* name);

//传输i2c数据
/*
bus：i2c总线设备
msgs[]：要传输的消息
num：消息的数量
*/
rt_size_t rt_i2c_transfer(struct rt_i2c_bus_device *bus,
                            struct rt_i2c_msg msgs[],
                            rt_uint32_t num);

2.2 消息结构体rt_i2c_msg

/*
addr：从机地址，0'7b
flags：传输标志
len：读写字节数
buf：读写数据缓存区
*/
struct rt_i2c_msg
{
    rt_uint16_t addr;
    rt_uint16_t flags;
    rt_uint16_t len;
    rt_uint8_t  *buf;
};

2.3 传输标志

#define RT_I2C_WR                0x0000    //写标志
#define RT_I2C_RD               (1u << 0)  //读标志
#define RT_I2C_ADDR_10BIT       (1u << 2)  /* this is a ten bit chip address */  //10位地址
#define RT_I2C_NO_START         (1u << 4)  //无起始信号
#define RT_I2C_IGNORE_NACK      (1u << 5)  //忽略应答
#define RT_I2C_NO_READ_ACK      (1u << 6)  /* when I2C reading, we do not ACK */  //读的时候不发送ACK
#define RT_I2C_NO_STOP          (1u << 7)  //无停止信号

三、示例

/*
 * Copyright (c) 2006-2018, RT-Thread Development Team
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * Change Logs:
 * Date           Author       Notes
 * 2018-08-15     misonyo      first implementation.
 */
/*
 * 程序清单：这是一个 I2C 设备使用例程
 * 例程导出了 i2c_aht10_sample 命令到控制终端
 * 命令调用格式：i2c_aht10_sample i2c1
 * 命令解释：命令第二个参数是要使用的I2C总线设备名称，为空则使用默认的I2C总线设备
 * 程序功能：通过 I2C 设备读取温湿度传感器 aht10 的温湿度数据并打印
*/

#include <rtthread.h>
#include <rtdevice.h>

#define AHT10_I2C_BUS_NAME          "i2c1"  /* 传感器连接的I2C总线设备名称 */
#define AHT10_ADDR                  0x38    /* 从机地址 */
#define AHT10_CALIBRATION_CMD       0xE1    /* 校准命令 */
#define AHT10_NORMAL_CMD            0xA8    /* 一般命令 */
#define AHT10_GET_DATA              0xAC    /* 获取数据命令 */

static struct rt_i2c_bus_device *i2c_bus = RT_NULL;     /* I2C总线设备句柄 */
static rt_bool_t initialized = RT_FALSE;                /* 传感器初始化状态 */

/* 写传感器寄存器 */
static rt_err_t write_reg(struct rt_i2c_bus_device *bus, rt_uint8_t reg, rt_uint8_t *data)
{
    rt_uint8_t buf[3];
    struct rt_i2c_msg msgs;

    buf[0] = reg; //cmd
    buf[1] = data[0];
    buf[2] = data[1];

    msgs.addr = AHT10_ADDR;
    msgs.flags = RT_I2C_WR;
    msgs.buf = buf;
    msgs.len = 3;

    /* 调用I2C设备接口传输数据 */
    if (rt_i2c_transfer(bus, &msgs, 1) == 1)
    {
        return RT_EOK;
    }
    else
    {
        return -RT_ERROR;
    }
}

/* 读传感器寄存器数据 */
static rt_err_t read_regs(struct rt_i2c_bus_device *bus, rt_uint8_t len, rt_uint8_t *buf)
{
    struct rt_i2c_msg msgs;

    msgs.addr = AHT10_ADDR;
    msgs.flags = RT_I2C_RD;
    msgs.buf = buf;
    msgs.len = len;

    /* 调用I2C设备接口传输数据 */
    if (rt_i2c_transfer(bus, &msgs, 1) == 1)
    {
        return RT_EOK;
    }
    else
    {
        return -RT_ERROR;
    }
}

static void read_temp_humi(float *cur_temp, float *cur_humi)
{
    rt_uint8_t temp[6];

    write_reg(i2c_bus, AHT10_GET_DATA, 0);      /* 发送命令 */
    read_regs(i2c_bus, 6, temp);                /* 获取传感器数据 */

    /* 湿度数据转换 */
    *cur_humi = (temp[1] << 12 | temp[2] << 4 | (temp[3] & 0xf0) >> 4) * 100.0 / (1 << 20);
    /* 温度数据转换 */
    *cur_temp = ((temp[3] & 0xf) << 16 | temp[4] << 8 | temp[5]) * 200.0 / (1 << 20) - 50;
}

static void aht10_init(const char *name)
{
    rt_uint8_t temp[2] = {0, 0};

    /* 查找I2C总线设备，获取I2C总线设备句柄 */
    i2c_bus = (struct rt_i2c_bus_device *)rt_device_find(name);

    if (i2c_bus == RT_NULL)
    {
        rt_kprintf("can't find %s device!\n", name);
    }
    else
    {
        write_reg(i2c_bus, AHT10_NORMAL_CMD, temp);
        rt_thread_mdelay(400);

        temp[0] = 0x08;
        temp[1] = 0x00;
        write_reg(i2c_bus, AHT10_CALIBRATION_CMD, temp);
        rt_thread_mdelay(400);
        initialized = RT_TRUE;
    }
}

static void i2c_aht10_sample(int argc, char *argv[])
{
    float humidity, temperature;
    char name[RT_NAME_MAX];

    humidity = 0.0;
    temperature = 0.0;

    if (argc == 2)
    {
        rt_strncpy(name, argv[1], RT_NAME_MAX);
    }
    else
    {
        rt_strncpy(name, AHT10_I2C_BUS_NAME, RT_NAME_MAX);
    }

    if (!initialized)
    {
        /* 传感器初始化 */
        aht10_init(name);
    }
    if (initialized)
    {
        /* 读取温湿度数据 */
        read_temp_humi(&temperature, &humidity);

        rt_kprintf("read aht10 sensor humidity   : %d.%d %%\n", (int)humidity, (int)(humidity * 10) % 10);
        rt_kprintf("read aht10 sensor temperature: %d.%d \n", (int)temperature, (int)(temperature * 10) % 10);
    }
    else
    {
        rt_kprintf("initialize sensor failed!\n");
    }
}
/* 导出到 msh 命令列表中 */
MSH_CMD_EXPORT(i2c_aht10_sample, i2c aht10 sample);