ICM20948 DMP代码详解（38）

接前一篇文章：ICM20948 DMP代码详解（37）

上一回继续解析inv_icm20948_set_slave_compass_id函数，解析了第3段代码，本回解析接下来的代码。为了便于理解和回顾，再次贴出该函数源码，在EMD-Core\sources\Invn\Devices\Drivers\ICM20948\Icm20948DataBaseDriver.c中，如下：

int inv_icm20948_set_slave_compass_id(struct inv_icm20948 *s, int id)
{
	int result = 0;
	(void)id;
 
	//result = inv_icm20948_wakeup_mems(s);
	//if (result)
	//	return result;
		
	inv_icm20948_prevent_lpen_control(s);
	activate_compass(s);
	
	inv_icm20948_init_secondary(s);
 
	// Set up the secondary I2C bus on 20630.
	inv_icm20948_set_secondary(s);
 
	//Setup Compass
	result = inv_icm20948_setup_compass_akm(s);
 
	//Setup Compass mounting matrix into DMP
	result |= inv_icm20948_compass_dmp_cal(s, s->mounting_matrix, s->mounting_matrix_secondary_compass);
	
	if (result)
		desactivate_compass(s);
 
	//result = inv_icm20948_sleep_mems(s);
	inv_icm20948_allow_lpen_control(s);
	return result;
}

4）inv_icm20948_set_secondary函数

代码片段如下：

	// Set up the secondary I2C bus on 20630.
	inv_icm20948_set_secondary(s);

inv_icm20948_set_secondary函数在EMD-Core\sources\Invn\Devices\Drivers\ICM20948\Icm20948DataBaseDriver.c，代码如下：

/**
*  @brief      Set up the secondary I2C bus on 20630.
*  @param[in]  MPU state varible
*  @return     0 if successful.
*/
int inv_icm20948_set_secondary(struct inv_icm20948 *s)
{
	int r = 0;
	static uint8_t lIsInited = 0;

	if(lIsInited == 0)
    {
		r  = inv_icm20948_write_single_mems_reg(s, REG_I2C_MST_CTRL, BIT_I2C_MST_P_NSR);
		r |= inv_icm20948_write_single_mems_reg(s, REG_I2C_MST_ODR_CONFIG, MIN_MST_ODR_CONFIG);

		lIsInited = 1;
	}

	return r;
}

REG_I2C_MST_CTRL、BIT_I2C_MST_P_NSR、REG_I2C_MST_ODR_CONFIG宏在EMD-Core\sources\Invn\Devices\Drivers\ICM20948\Icm20948Defs.h中，定义如下：

/* bank 3 register map */
#define REG_I2C_MST_ODR_CONFIG  (BANK_3 | 0x0)

#define REG_I2C_MST_CTRL        (BANK_3 | 0x01)
#define BIT_I2C_MST_P_NSR               0x10

#define REG_I2C_MST_DELAY_CTRL  (BANK_3 | 0x02)

MIN_MST_ODR_CONFIG宏在EMD-Core\sources\Invn\Devices\Drivers\ICM20948\Icm20948Defs.h中，定义如下：

#define MIN_MST_ODR_CONFIG       4

综上，以下代码片段的意思是：

r  = inv_icm20948_write_single_mems_reg(s, REG_I2C_MST_CTRL, BIT_I2C_MST_P_NSR);

写I2C_MST_CTRL寄存器的值为0x10，即I2C_MST_CLK[3:0]设置为0b0000；

 MULT_MST_EN位为0；I2C_MST_P_NSR位为1。

以下代码片段的意思是：

		r |= inv_icm20948_write_single_mems_reg(s, REG_I2C_MST_ODR_CONFIG, MIN_MST_ODR_CONFIG);

写I2C_MST_ODR_CONFIG寄存器的值为4（0x04），即I2C_MST_ODR_CONFIG[3:0]设置为0b0000。

同时，设置lIsInited变量的值为1。

至此，inv_icm20948_set_secondary函数就解析完了。inv_icm20948_set_slave_compass_id函数后续内容的解析请看下回。