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接前一篇文章：ICM20948 DMP代码详解（14）

上一回开始对icm20948_sensor_setup函数中第3段代码即inv_icm20948_initialize函数进行解析。为了便于理解和回顾，再次贴出其源码，在EMD-Core\sources\Invn\Devices\Drivers\ICM20948\Icm20948Setup.c中，如下：

int inv_icm20948_initialize(struct inv_icm20948 * s, const uint8_t *dmp3_image, uint32_t dmp3_image_size)
{if(s->serif.is_spi) {/* Hardware initialization */// No image to be loaded from flash, no pointer to pass.if (inv_icm20948_initialize_lower_driver(s, SERIAL_INTERFACE_SPI, dmp3_image, dmp3_image_size)) {return -1;}}else {/* Hardware initialization */// No image to be loaded from flash, no pointer to pass.if (inv_icm20948_initialize_lower_driver(s, SERIAL_INTERFACE_I2C, dmp3_image, dmp3_image_size)) {return -1;}}return 0;
}

该函数主要是调用了inv_icm20948_initialize_lower_driver，其在EMD-Core\sources\Invn\Devices\Drivers\ICM20948\Icm20948DataBaseDriver.c中，代码如下：

/** Should be called once on power up. Loads DMP3, initializes internal variables needed 
*   for other lower driver functions.
*/
int inv_icm20948_initialize_lower_driver(struct inv_icm20948 *s, enum SMARTSENSOR_SERIAL_INTERFACE type, const uint8_t *dmp3_image, uint32_t dmp3_image_size)
{int result = 0;static unsigned char data;// set static variables->sAllowLpEn = 1;s->s_compass_available = 0;// ICM20948 do not support the proximity sensor for the moment.// s_proximity_available variable is nerver changess->s_proximity_available = 0;// Set varialbes to default valuesmemset(&s->base_state, 0, sizeof(s->base_state));s->base_state.pwr_mgmt_1 = BIT_CLK_PLL;s->base_state.pwr_mgmt_2 = BIT_PWR_ACCEL_STBY | BIT_PWR_GYRO_STBY | BIT_PWR_PRESSURE_STBY;s->base_state.serial_interface = type;result |= inv_icm20948_read_mems_reg(s, REG_USER_CTRL, 1, &s->base_state.user_ctrl);result |= inv_icm20948_wakeup_mems(s);result |= inv_icm20948_read_mems_reg(s, REG_WHO_AM_I, 1, &data);/* secondary cycle mode should be set all the time */data = BIT_I2C_MST_CYCLE|BIT_ACCEL_CYCLE|BIT_GYRO_CYCLE;// Set default mode to low power moderesult |= inv_icm20948_set_lowpower_or_highperformance(s, 0);// Disable Ivory DMP.if(s->base_state.serial_interface == SERIAL_INTERFACE_SPI)   s->base_state.user_ctrl = BIT_I2C_IF_DIS;elses->base_state.user_ctrl = 0;result |= inv_icm20948_write_single_mems_reg(s, REG_USER_CTRL, s->base_state.user_ctrl);//Setup Ivory DMP.result |= inv_icm20948_load_firmware(s, dmp3_image, dmp3_image_size);if(result)return result;elses->base_state.firmware_loaded = 1;result |= inv_icm20948_set_dmp_address(s);// Turn off all sensors on DMP by default.//result |= dmp_set_data_output_control1(0);   // FIXME in DMP, these should be off by default.result |= dmp_icm20948_reset_control_registers(s);// set FIFO watermark to 80% of actual FIFO sizeresult |= dmp_icm20948_set_FIFO_watermark(s, 800);// Enable Interrupts.data = 0x2;result |= inv_icm20948_write_mems_reg(s, REG_INT_ENABLE, 1, &data); // Enable DMP Interruptdata = 0x1;result |= inv_icm20948_write_mems_reg(s, REG_INT_ENABLE_2, 1, &data); // Enable FIFO Overflow Interrupt// TRACKING : To have accelerometers datas and the interrupt without gyro enables.data = 0XE4;result |= inv_icm20948_write_mems_reg(s, REG_SINGLE_FIFO_PRIORITY_SEL, 1, &data);// Disable HW temp fixinv_icm20948_read_mems_reg(s, REG_HW_FIX_DISABLE,1,&data);data |= 0x08;inv_icm20948_write_mems_reg(s, REG_HW_FIX_DISABLE,1,&data);// Setup MEMs properties.s->base_state.accel_averaging = 1; //Change this value if higher sensor sample avergaing is required.s->base_state.gyro_averaging = 1;  //Change this value if higher sensor sample avergaing is required.inv_icm20948_set_gyro_divider(s, FIFO_DIVIDER);       //Initial sampling rate 1125Hz/19+1 = 56Hz.inv_icm20948_set_accel_divider(s, FIFO_DIVIDER);      //Initial sampling rate 1125Hz/19+1 = 56Hz.// Init the sample rate to 56 Hz for BAC,STEPC and B2Sdmp_icm20948_set_bac_rate(s, DMP_ALGO_FREQ_56);dmp_icm20948_set_b2s_rate(s, DMP_ALGO_FREQ_56);// FIFO Setup.result |= inv_icm20948_write_single_mems_reg(s, REG_FIFO_CFG, BIT_SINGLE_FIFO_CFG); // FIFO Config. fixme do once? burst write?result |= inv_icm20948_write_single_mems_reg(s, REG_FIFO_RST, 0x1f); // Reset all FIFOs.result |= inv_icm20948_write_single_mems_reg(s, REG_FIFO_RST, 0x1e); // Keep all but Gyro FIFO in reset.result |= inv_icm20948_write_single_mems_reg(s, REG_FIFO_EN, 0x0); // Slave FIFO turned off.result |= inv_icm20948_write_single_mems_reg(s, REG_FIFO_EN_2, 0x0); // Hardware FIFO turned off.s->base_state.lp_en_support = 1;if(s->base_state.lp_en_support == 1)inv_icm20948_set_chip_power_state(s, CHIP_LP_ENABLE, 1);result |= inv_icm20948_sleep_mems(s);   return result;
}

上一回讲了函数一开始的成员设置，本回继续往下对该函数进行解析。当前来到以下代码片段：

	result |= inv_icm20948_read_mems_reg(s, REG_USER_CTRL, 1, &s->base_state.user_ctrl);

inv_icm20948_read_mems_reg函数在EMD-Core\sources\Invn\Devices\Drivers\ICM20948\Icm20948Transport.c中，代码如下：

/**
*  @brief      Read data from a register on MEMs.
*  @param[in]  Register address
*  @param[in]  Length of data
*  @param[in]  Data to be written
*  @return     0 if successful.
*/
int inv_icm20948_read_mems_reg(struct inv_icm20948 *s, uint16_t reg, unsigned int length, unsigned char *data)
{int result = 0;unsigned int bytesRead = 0;unsigned char regOnly = (unsigned char)(reg & 0x7F);unsigned char i, dat[INV_MAX_SERIAL_READ];unsigned char power_state = inv_icm20948_get_chip_power_state(s);if((power_state & CHIP_AWAKE) == 0)   // Wake up chip since it is asleepresult = inv_icm20948_set_chip_power_state(s, CHIP_AWAKE, 1);if(check_reg_access_lp_disable(s, reg))   // Check if register needs LP_EN to be disabledresult |= inv_icm20948_set_chip_power_state(s, CHIP_LP_ENABLE, 0);  //Disable LP_ENresult |= inv_set_bank(s, reg >> 7);while (bytesRead<length) {int thisLen = min(INV_MAX_SERIAL_READ, length-bytesRead);if(s->base_state.serial_interface == SERIAL_INTERFACE_SPI) {result |= inv_icm20948_read_reg(s, regOnly+bytesRead, &dat[bytesRead], thisLen);} else {result |= inv_icm20948_read_reg(s, regOnly+bytesRead, &data[bytesRead],thisLen);}if (result)return result;bytesRead += thisLen;}if(s->base_state.serial_interface == SERIAL_INTERFACE_SPI) {for (i=0; i< length; i++) {*data= dat[i];data++;}}if(check_reg_access_lp_disable(s, reg))    // Check if register needs LP_EN to be enabled  result |= inv_icm20948_set_chip_power_state(s, CHIP_LP_ENABLE, 1);  //Enable LP_ENreturn result;
}

要弄懂这个函数，必须先弄清楚其中的几个函数。一个一个来看。

（1）inv_icm20948_get_chip_power_state函数

inv_icm20948_get_chip_power_state函数在EMD-Core\sources\Invn\Devices\Drivers\ICM20948\Icm20948DataBaseDriver.c中，代码如下：

/*!*******************************************************************************   @return    Current wake status of the Ivory chip.*******************************************************************************/
uint8_t inv_icm20948_get_chip_power_state(struct inv_icm20948 *s)
{return s->base_state.wake_state;
}

其实就是得到s->base_state.wake_state的值。前文书中曾讲到，在inv_icm20948_initialize_lower_driver函数中对于s->base_state整个进行了清零，因此这时的值必然是0。

（2）inv_icm20948_set_chip_power_state函数

inv_icm20948_set_chip_power_state函数也是在EMD-Core\sources\Invn\Devices\Drivers\ICM20948\Icm20948DataBaseDriver.c中，代码如下：

/*!*******************************************************************************   @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_ens->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_ens->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 ONstatus = 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 offstatus = 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 switchreturn status;
}

这要结合inv_icm20948_read_mems_reg函数中的调用来看，代码片段如下：

	if((power_state & CHIP_AWAKE) == 0)   // Wake up chip since it is asleepresult = inv_icm20948_set_chip_power_state(s, CHIP_AWAKE, 1);if(check_reg_access_lp_disable(s, reg))   // Check if register needs LP_EN to be disabledresult |= inv_icm20948_set_chip_power_state(s, CHIP_LP_ENABLE, 0);  //Disable LP_EN

一共两次调用，一次是CHIP_AWAKE，另一次是CHIP_LP_ENABLE。正好对应inv_icm20948_set_chip_power_state函数中switch的两个case。依次看一下这两个分支：

1）case CHIP_AWAKE

相应代码片段如下：

		case CHIP_AWAKE:    if(on_off){if((s->base_state.wake_state & CHIP_AWAKE) == 0) {// undo sleep_ens->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_ens->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;

如果inv_icm20948_set_chip_power_state函数的第3个参数unsigned char on_off传入的值为1，同时状态与本次设置不同，则清除s->base_state.pwr_mgmt_1中的BIT_SLEEP位；写入ICM20948的REG_PWR_MGMT_1寄存器；之后将s->base_state.wake_state中的CHIP_AWAKE置位，并延时100us。

如果on_off传入的值为0，同时状态与本次设置不同，则置位s->base_state.pwr_mgmt_1中的BIT_SLEEP位；写入ICM20948的REG_PWR_MGMT_1寄存器；之后清除s->base_state.wake_state中的CHIP_AWAKE位，并延时100us。

2）case CHIP_LP_ENABLE

相应代码片段如下：

		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 ONstatus = 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 offstatus = 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;

在s->base_state.lp_en_support设置的情况下，判断体代码才有效。此时并未设置过，还是之前在inv_icm20948_initialize_lower_driver函数中设置的清零状态。

不过这里也先解析一下，免得以后还得回来再解析。

如果inv_icm20948_set_chip_power_state函数的第3个参数unsigned char on_off传入的值为1，同时状态与本次设置不同，则置位s->base_state.pwr_mgmt_1中的BIT_LP_EN位；写入ICM20948的REG_PWR_MGMT_1寄存器；之后将s->base_state.wake_state中的CHIP_LP_ENABLE置位，并延时100us。

如果on_off传入的值为0，同时状态与本次设置不同，则清除s->base_state.pwr_mgmt_1中的BIT_LP_EN位；写入ICM20948的REG_PWR_MGMT_1寄存器；之后清除s->base_state.wake_state中的CHIP_LP_ENABLE位，并延时100us。

inv_icm20948_set_chip_power_state函数中还有三个函数要讲一下，分别是：

1）inv_icm20948_write_single_mems_reg_core函数

2）inv_icm20948_get_lpen_control函数

3）inv_icm20948_sleep_100us函数

对于这三个函数的解析，请看下回。