接前一篇文章：ICM20948 DMP代码详解（25）
上一回解析完了inv_icm20948_load_firmware函数，回到inv_icm20948_initialize_lower_driver函数中，继续往下进行解析。为了便于理解和回顾，再次贴出inv_icm20948_initialize_lower_driver函数源码，在EMD-Core\sources\Invn\Devices\Drivers\ICM20948\Icm20948DataBaseDriver.c中，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;
}当前来到以下代码片段：
result |= inv_icm20948_set_dmp_address(s);inv_icm20948_set_dmp_address函数在EMD-Core\sources\Invn\Devices\Drivers\ICM20948\Icm20948DataBaseDriver.c中，代码如下：
int inv_icm20948_set_dmp_address(struct inv_icm20948 * s)
{int result;unsigned char dmp_cfg[2] = {0};unsigned short config;// Write DMP Start addressinv_icm20948_get_dmp_start_address(s, &config);/* setup DMP start address and firmware */dmp_cfg[0] = (unsigned char)((config >> 8) & 0xff);dmp_cfg[1] = (unsigned char)(config & 0xff);result = inv_icm20948_write_mems_reg(s, REG_PRGM_START_ADDRH, 2, dmp_cfg);return result;
}inv_icm20948_get_dmp_start_address函数在EMD-Core\sources\Invn\Devices\Drivers\ICM20948\Icm20948Dmp3Driver.c中，代码如下：
/** Loads the dmp firmware for the icm20948 part.
* @param[out] dmp_cnfg The config item
*/
void inv_icm20948_get_dmp_start_address(struct inv_icm20948 *s, unsigned short *dmp_cnfg)
{(void)s;*dmp_cnfg = DMP_START_ADDRESS;
}DMP_START_ADDRESS宏在EMD-Core\sources\Invn\Devices\Drivers\ICM20948\Icm20948Dmp3Driver.c中，定义如下：
#define DMP_START_ADDRESS ((unsigned short)0x1000)那么dmp_cfg[0]的值就是0x10，dmp_cfg[1]的值是0x00。
REG_PRGM_START_ADDRH宏在EMD-Core\sources\Invn\Devices\Drivers\ICM20948\Icm20948Defs.h中，定义如下：
#define REG_PRGM_START_ADDRH (BANK_2 | 0x50)bank2的0x50寄存器在ICM20948芯片手册中又没有给出，又属于“后门”寄存器。根据宏定义的字面意义，是编程的起始地址，0x50中存放高字节，0x51中存放低字节。
综合来看，inv_icm20948_set_dmp_address函数的作用是将0x1000这一地址（DMP起始地址）分两个字节写入到bank2的0x50和0x51两个寄存器（编程起始地址）中。
至此，inv_icm20948_set_dmp_address函数就解析完了。回到inv_icm20948_initialize_lower_driver函数中，下一回继续解析inv_icm20948_initialize_lower_driver函数中的后续代码。
