接前一篇文章：ICM20948 DMP代码详解（15）

上一回讲到了inv_icm20948_initialize函数中的inv_icm20948_initialize_lower_driver函数中的inv_icm20948_read_mems_reg函数中的inv_icm20948_set_chip_power_state函数。再次贴出该函数源码：

/*!
 ******************************************************************************
 *   @brief     This function sets the power state of the Ivory chip 
 *				loop
 *   @param[in] Function - CHIP_AWAKE, CHIP_LP_ENABLE
 *   @param[in] On/Off - The functions are enabled if previously disabled and 
                disabled if previously enabled based on the value of On/Off.
 ******************************************************************************
 */ 
int inv_icm20948_set_chip_power_state(struct inv_icm20948 *s, unsigned char func, unsigned char on_off)
{
	int status = 0;
 
	switch(func) {
 
		case CHIP_AWAKE:    
			if(on_off){
				if((s->base_state.wake_state & CHIP_AWAKE) == 0) {// undo sleep_en
					s->base_state.pwr_mgmt_1 &= ~BIT_SLEEP;
					status = inv_icm20948_write_single_mems_reg_core(s, REG_PWR_MGMT_1, s->base_state.pwr_mgmt_1);
					s->base_state.wake_state |= CHIP_AWAKE;
					inv_icm20948_sleep_100us(1); // after writing the bit wait 100 Micro Seconds
				}
			} else {
				if(s->base_state.wake_state & CHIP_AWAKE) {// set sleep_en
					s->base_state.pwr_mgmt_1 |= BIT_SLEEP;
					status = inv_icm20948_write_single_mems_reg_core(s, REG_PWR_MGMT_1, s->base_state.pwr_mgmt_1);
					s->base_state.wake_state &= ~CHIP_AWAKE;
					inv_icm20948_sleep_100us(1); // after writing the bit wait 100 Micro Seconds
				}
			}
		break;
 
		case CHIP_LP_ENABLE:
			if(s->base_state.lp_en_support == 1) {
				if(on_off) {
					if( (inv_icm20948_get_lpen_control(s)) && ((s->base_state.wake_state & CHIP_LP_ENABLE) == 0)){
						s->base_state.pwr_mgmt_1 |= BIT_LP_EN; // lp_en ON
						status = inv_icm20948_write_single_mems_reg_core(s, REG_PWR_MGMT_1, s->base_state.pwr_mgmt_1);
						s->base_state.wake_state |= CHIP_LP_ENABLE;
					}
				} else {
					if(s->base_state.wake_state & CHIP_LP_ENABLE){
						s->base_state.pwr_mgmt_1 &= ~BIT_LP_EN; // lp_en off
						status = inv_icm20948_write_single_mems_reg_core(s, REG_PWR_MGMT_1, s->base_state.pwr_mgmt_1);
						s->base_state.wake_state &= ~CHIP_LP_ENABLE;
						inv_icm20948_sleep_100us(1); // after writing the bit wait 100 Micro Seconds
					}
				}
			}
		break;
 
		default:
		break;
 
	}// end switch
 
	return status;
}

上一回说其中还有3个函数需要解析，本回就来一一进行解析。

1）inv_icm20948_write_single_mems_reg_core函数

inv_icm20948_write_single_mems_reg_core函数在C:\Users\ns\Ykq\eMD-SmartMotion-ICM20948-1.1.1\EMD-Core\sources\Invn\Devices\Drivers\ICM20948\Icm20948Transport.c中，代码如下：

/**
*  @brief      Write single byte of data to a register on MEMs with no power control
*  @param[in]  Register address
*  @param[in]  Data to be written
*  @return     0 if successful.
*/
int inv_icm20948_write_single_mems_reg_core(struct inv_icm20948 *s, uint16_t reg, const uint8_t data)
{
	int result = 0;
	unsigned char regOnly = (unsigned char)(reg & 0x7F);

	result |= inv_set_bank(s, reg >> 7);
	result |= inv_icm20948_write_reg(s, regOnly, &data, 1);

	return result;
}

函数的功能是在没有电源控制的情况下，将单字节数据写入MEMs上的寄存器。实际上分为两步，先设置bank，后写bank中的寄存器。

inv_set_bank函数也在EMD-Core\sources\Invn\Devices\Drivers\ICM20948\Icm20948Transport.c中，代码如下：

/**
*  @brief      Set up the register bank register for accessing registers in 20630.
*  @param[in]  register bank number
*  @return     0 if successful.
*/

static int inv_set_bank(struct inv_icm20948 *s, unsigned char bank)
{
	int result;
	//if bank reg was set before, just return
	if(bank==s->lastBank) 
		return 0;
	else 
		s->lastBank = bank;

	result = inv_icm20948_read_reg(s, REG_BANK_SEL, &s->reg, 1);

	if (result)
		return result;

	s->reg &= 0xce;
	s->reg |= (bank << 4);
	result = inv_icm20948_write_reg(s, REG_BANK_SEL, &s->reg, 1);

	return result;
}

其实还是通用的先读后写流程。先读取REG_BANK_SEL的内容，设置相关位，再写回去。

REG_BANK_SEL宏在EMD-Core\sources\Invn\Devices\Drivers\ICM20948\Icm20948Defs.h中定义，如下：

/* register for all banks */
#define REG_BANK_SEL            0x7F

对应于ICM20948芯片手册中的：

bit5:4正好对应的就是上边代码中的

	s->reg &= 0xce;
	s->reg |= (bank << 4);

inv_icm20948_write_reg函数在EMD-Core\sources\Invn\Devices\Drivers\ICM20948\Icm20948Transport.c中，代码如下：

int inv_icm20948_write_reg(struct inv_icm20948 *s, uint8_t reg, const uint8_t *buf, uint32_t len)
{
	return inv_icm20948_serif_write_reg(&s->serif, reg, buf, len);
}

参考前文书解析的inv_icm20948_read_reg函数的调用流程（ICM20948 DMP代码详解（9）-CSDN博客）：

inv_icm20948_read_reg_one函数   --->

        inv_icm20948_read_reg函数   --->

                inv_icm20948_serif_read_reg函数   --->

                        idd_io_hal_read_reg函数

inv_icm20948_write_reg函数的调用流程也是类似的。这里也列一下。

inv_icm20948_serif_write_reg函数在EMD-Core\sources\Invn\Devices\Drivers\ICM20948\Icm20948Serif.h中，代码如下：

static inline int inv_icm20948_serif_write_reg(struct inv_icm20948_serif * s,
		uint8_t reg, const uint8_t * buf, uint32_t len)
{
	assert(s);

	if(len > s->max_write)
		return INV_ERROR_SIZE;

	if(s->write_reg(s->context, reg, buf, len) != 0)
		return INV_ERROR_TRANSPORT;

	return 0;
}

s->wrire_reg对应的就是idd_io_hal_write_reg函数。

idd_io_hal_write_reg函数在EMD-App\src\ICM20948\system.c中，代码如下：

int idd_io_hal_write_reg(void * context, uint8_t reg, const uint8_t * wbuffer, uint32_t wlen){
	(void)context;
#if SERIF_TYPE_SPI
	return spi_master_transfer_tx(NULL, reg, wbuffer, wlen);
#else /* SERIF_TYPE_I2C */
	return i2c_master_write_register(I2C_Address, reg, wlen, wbuffer);
#endif	
}

和idd_io_hal_read_reg函数一样，idd_io_hal_write_reg函数中调用的i2c_master_write_register函数如果是自己的板子，也是要换成自己平台下的i2c写函数。

本回内容比较多了，余下内容放到下一回继续解析。