基于单片机的I2C接口SHT20传感器采样设计

7.1 原理图分析

查看EK-RA6M4的原理图，如下图所示，该开发板上的MikroBus接口上有提供一个I2C接口。

根据原理图可知，I2C1接口的两个引脚分别为：

按键	SDA1	SCL1
引脚	P511	P512

这里我们将在该I2C接口上连接 SHT20 传感器(3.3V供电)，实时采样当前环境的温湿度情况。

7.2 I2C接口配置

首先，在FSP配置中将I2C1所用的两个GPIO口配置成I2C模式。

接着选择 Stacks ，点击 "New Stack" -> "Connectivity" -> "I2C Master(r_iic_master)" 添加I2C Master协议栈。

接下来设置I2C Master的相关配置，并重新生成代码。

• 通过 Name 字段可以修改I2C的设备名称为 g_i2c1_master，它将在IDE自动生成的文件 ra_gen/hal_data.c/h 中定义I2C操作相关的变量；
• 通过 Channel 字段可以修改I2C的通道号，这里设置为1，下面的 Pins 将自动选择 P511和 P512 这个引脚；
• 通过 Slava Address 字段可以设置I2C从设备的地址，其中SHT20 的从设备地址为 0x40；
• 通过 Callback 字段设置I2C收发的中断回调函数，它将配置在 g_i2c1_master_cfg 变量中，该函数需要我们自己实现；
• 在这里我们也可以修改I2C中断的优先级为2级别；

7.3 源码修改

创建SHT20温湿度传感器操作相关的头文件 src/bsp_sht20.h 如下：

#ifndef BSP_SHT20_H_
#define BSP_SHT20_H_

#include 

int sht20_init(void);

void sht20_deinit(void);

int sht20_read_data(double *temp, double *rh);

#endif /* BSP_SHT20_H_ */

创建SHT20温湿度传感器操作相关的c文件 src/bsp_sht20.c 如下：

#include 
#include "hal_data.h"
#include "bsp_sht20.h"
#include "r_i2c_master_api.h"

#define RESET_VALUE         0x00

static int i2c_write(uint8_t *data, uint32_t bytes, bool const restart);
static int i2c_read(uint8_t *buf, uint32_t size, bool const restart);

int sht20_init(void)
{
    fsp_err_t err     = FSP_SUCCESS;

    /* Open I2C master */
    err = R_IIC_MASTER_Open(&g_i2c1_master_ctrl, &g_i2c1_master_cfg);
    if (FSP_SUCCESS != err)
    {
        printf("** R_IIC_MASTER_Open API failed ** 
");
        return err;
    }

#if 0
    /* SHT20 sensor soft reset */
    uint8_t           buf[1] = 0xfe;
    err = i2c_write(buf, 1, true);
    if (FSP_SUCCESS != err)
    {
        printf("** SHT20 sensor soft reset failed ** 
");
        return err;
    }

    R_BSP_SoftwareDelay(50, BSP_DELAY_UNITS_MILLISECONDS);
#endif

    return 0;
}

void sht20_deinit(void)
{
    R_IIC_MASTER_Close (&g_i2c1_master_ctrl);
    return ;
}

int sht20_read_data(double *temp, double *rh)
{
    fsp_err_t err     = FSP_SUCCESS;
    uint8_t           buf[4];

    /* send trigger temperature measure command and read the data */
    buf[0]=0xF3;
    err = i2c_write(buf, 1, true);
    if (FSP_SUCCESS != err)
    {
        printf("** SHT20 send trigger temperature measure command failed ** 
");
        return err;
    }

    /* datasheet: typ=66, max=85 */
    R_BSP_SoftwareDelay(85, BSP_DELAY_UNITS_MILLISECONDS);

    /* read temperature measure data */
    memset(buf, 0, sizeof(buf) );
    err = i2c_read(buf, 3, false);
    if (FSP_SUCCESS != err)
    {
        printf("** SHT20 read ID from Location 1 failed ** 
");
        return err;
    }
    *temp = 175.72 * (((((int) buf[0]) << 8) + buf[1]) / 65536.0) - 46.85;

    /* send trigger humidity measure command and read the data */
    buf[0] = 0xF5;
    err = i2c_write(buf, 1, true);
    if (FSP_SUCCESS != err)
    {
        printf("** SHT20 send trigger humidity measure command failed ** 
");
        return err;
    }

    /* datasheet: typ=22, max=29 */
    R_BSP_SoftwareDelay(29, BSP_DELAY_UNITS_MILLISECONDS);

    /* read humidity measure data */
    memset(buf, 0, sizeof(buf) );
    err = i2c_read(buf, 3, false);
    if (FSP_SUCCESS != err)
    {
        printf("** SHT20 read ID from Location 1 failed ** 
");
        return err;
    }
    *rh = 125 * (((((int) buf[0]) << 8) + buf[1]) / 65536.0) - 6;

    return 0;
}


/* Reading I2C call back event through i2c_Master callback */
static volatile i2c_master_event_t i2c_event = I2C_MASTER_EVENT_ABORTED;

void i2c1_master_callback(i2c_master_callback_args_t *p_args)
{
    if (NULL != p_args)
    {
        /* capture callback event for validating the i2c transfer event*/
        i2c_event = p_args->event;
    }
}
static fsp_err_t validate_i2c_event(void)
{
    uint16_t local_time_out = UINT16_MAX;

    /* resetting call back event capture variable */
    i2c_event = (i2c_master_event_t)RESET_VALUE;

    do
    {
        /* This is to avoid infinite loop */
        --local_time_out;

        if(RESET_VALUE == local_time_out)
        {
            return FSP_ERR_TRANSFER_ABORTED;
        }

    }while(i2c_event == RESET_VALUE);

    if(i2c_event != I2C_MASTER_EVENT_ABORTED)
    {
        i2c_event = (i2c_master_event_t)RESET_VALUE;  // Make sure this is always Reset before return
        return FSP_SUCCESS;
    }

    i2c_event = (i2c_master_event_t)RESET_VALUE; // Make sure this is always Reset before return
    return FSP_ERR_TRANSFER_ABORTED;
}

static int i2c_write(uint8_t *data, uint32_t bytes, bool const restart)
{
    fsp_err_t err     = FSP_SUCCESS;

    if( !data || bytes<=0 )
        return FSP_ERR_INVALID_ARGUMENT;

    err = R_IIC_MASTER_Write(&g_i2c1_master_ctrl, data, bytes, restart);
    if (FSP_SUCCESS != err)
    {
        printf("** R_IIC_MASTER_Write API failed ** 
");
        return err;
    }

    err = validate_i2c_event();
    if (FSP_SUCCESS != err)
    {
        printf("** I2C write validate failed, err=%d ** 
", err);
        return err;
    }

    return FSP_SUCCESS;
}

static int i2c_read(uint8_t *buf, uint32_t size, bool const restart)
{
    fsp_err_t err     = FSP_SUCCESS;

    if( !buf || size<=0 )
        return FSP_ERR_INVALID_ARGUMENT;

    err = R_IIC_MASTER_Read(&g_i2c1_master_ctrl, buf, size, restart);
    if (FSP_SUCCESS != err)
    {
        printf("** R_IIC_MASTER_Write API failed ** 
");
        return err;
    }

    err = validate_i2c_event();
    if (FSP_SUCCESS != err)
    {
        printf("** I2C read validate failed, err=%d ** 
", err);
        return err;
    }

    return FSP_SUCCESS;
}

修改 src/hal_entry.c 源文件，在里面添加 sht20 温湿度传感器采样的代码。

... ...
#include "bsp_sht20.h"
... ...
void hal_entry(void)
{
    double      temp = 0.0;
    double      rh = 0.0;    
    ... ...
    sht20_init();
    while (1)
    {
        ... ...
        sht20_read_data(&temp, &rh);
        printf("temp: %.3f  RH: %.3f
", temp, rh);        
    }
}

7.4 编译运行

代码修改完成后，在开发板上编译运行。

这时串口终端上将会实时打印SHT20传感器采样的温湿度。