接前一篇文章：ICM20948 DMP代码详解（5）
前一篇文章解析了EMP-App中的入口函数main()中重点关注的第1段代码，本回继续往下进行解析。为了便于理解和回顾，再次贴出main函数源码：
int main (void)
{
int rc = 0;
/* Hardware initialization */
sysclk_init();
board_init();
sysclk_enable_peripheral_clock(ID_TC0);
/* Configure Device - Host Interface */
configure_console();
#ifdef INV_MSG_ENABLE
/* Setup message logging */
INV_MSG_SETUP(INV_MSG_ENABLE, msg_printer);
#endif
INV_MSG(INV_MSG_LEVEL_INFO, "##########################");
INV_MSG(INV_MSG_LEVEL_INFO, " ICM20948 example ");
INV_MSG(INV_MSG_LEVEL_INFO, " Ver: %s", EMD_RELEASE_VERSION_STRING);
INV_MSG(INV_MSG_LEVEL_INFO, "##########################");
/* Initialize External Sensor Interrupt */
ext_int_initialize(&ext_interrupt_handler);
interface_initialize();
/* Configure sysTick Timer */
SysTick_Config(sysclk_get_cpu_hz() / MILLISECONDS_PER_SECOND);
/*
* Initialize icm20948 serif structure
*/
struct inv_icm20948_serif icm20948_serif;
icm20948_serif.context = 0; /* no need */
icm20948_serif.read_reg = idd_io_hal_read_reg;
icm20948_serif.write_reg = idd_io_hal_write_reg;
icm20948_serif.max_read = 1024*16; /* maximum number of bytes allowed per serial read */
icm20948_serif.max_write = 1024*16; /* maximum number of bytes allowed per serial write */
icm20948_serif.is_spi = interface_is_SPI();
/*
* Reset icm20948 driver states
*/
inv_icm20948_reset_states(&icm_device, &icm20948_serif);
inv_icm20948_register_aux_compass(&icm_device, INV_ICM20948_COMPASS_ID_AK09916, AK0991x_DEFAULT_I2C_ADDR);
/*
* Setup the icm20948 device
*/
rc = icm20948_sensor_setup();
/*
* Now that Icm20948 device was initialized, we can proceed with DMP image loading
* This step is mandatory as DMP image are not store in non volatile memory
*/
rc += load_dmp3();
check_rc(rc, "Error sensor_setup/DMP loading.");
/*
* Initialize Dynamic protocol stuff
*/
DynProTransportUart_init(&transport, iddwrapper_transport_event_cb, 0);
DynProtocol_init(&protocol, iddwrapper_protocol_event_cb, 0);
InvScheduler_init(&scheduler);
InvScheduler_initTask(&scheduler, &commandHandlerTask, "commandHandlerTask", CommandHandlerTaskMain, 0, INVSCHEDULER_TASK_PRIO_MIN, 1);
InvScheduler_initTask(&scheduler, &blinkerLedTask, "blinkerLedTask", BlinkerLedTaskMain, 0, INVSCHEDULER_TASK_PRIO_MIN+1, 1000000/SCHEDULER_PERIOD);
InvScheduler_startTask(&blinkerLedTask, 0);
InvScheduler_startTask(&commandHandlerTask, 0);
hw_timer_start(20); // Start the timestamp timer at 20 Hz.
while (1)
{
InvScheduler_dispatchTasks(&scheduler);
if (irq_from_device == 1) {
inv_icm20948_poll_sensor(&icm_device, (void *)0, build_sensor_event_data);
__disable_irq();
irq_from_device = 0;
__enable_irq();
}
}
return 0;
}接下来是第2段代码片段：
/*
* Reset icm20948 driver states
*/
inv_icm20948_reset_states(&icm_device, &icm20948_serif);
inv_icm20948_register_aux_compass(&icm_device, INV_ICM20948_COMPASS_ID_AK09916, AK0991x_DEFAULT_I2C_ADDR);inv_icm20948_reset_states函数在EMD-Core\sources\Invn\Devices\Drivers\ICM20948\Icm20948.h中，属于内联函数，代码如下：
/** @brief Reset and initialize driver states
* @param[in] s handle to driver states structure
*/
static inline void inv_icm20948_reset_states(struct inv_icm20948 * s,
const struct inv_icm20948_serif * serif)
{
assert(icm20948_instance == 0);
memset(s, 0, sizeof(*s));
s->serif = *serif;
icm20948_instance = s;
}函数的第2个参数const struct inv_icm20948_serif * serif对应的实参就是上一回分析的、在main函数中新建并初始化的icm20948_serif。
而第1个参数对应的实参为&icm_device。icm_device是一个全局变量，在EMD-App\src\ICM20948\sensor.c中定义，代码如下：
/*
* Just a handy variable to handle the icm20948 object
*/
inv_icm20948_t icm_device;inv_icm20948_t的定义在EMD-Core\sources\Invn\Devices\Drivers\ICM20948\Icm20948.h中，代码如下：
typedef struct inv_icm20948 {
struct inv_icm20948_serif serif;
/** @brief struct for the base_driver : this contains the Mems information */
struct base_driver_t
{
unsigned char wake_state;
chip_lp_ln_mode_icm20948_t chip_lp_ln_mode;
unsigned char pwr_mgmt_1;
unsigned char pwr_mgmt_2;
unsigned char user_ctrl;
unsigned char gyro_div;
unsigned short secondary_div;
short accel_div;
unsigned char gyro_averaging;
unsigned char accel_averaging;
uint8_t gyro_fullscale;
uint8_t accel_fullscale;
uint8_t lp_en_support:1;
uint8_t firmware_loaded:1;
uint8_t serial_interface;
uint8_t timebase_correction_pll;
}base_state;
/* secondary device support */
struct inv_icm20948_secondary_states {
struct inv_icm20948_secondary_reg {
uint16_t addr;
uint16_t reg;
uint16_t ctrl;
uint16_t d0;
} slv_reg[4];
unsigned char sSavedI2cOdr;
/* compass support */
uint8_t compass_sens[3];
long final_matrix[9];
const int16_t *st_upper;
const int16_t *st_lower;
int scale;
uint8_t dmp_on;
uint8_t secondary_resume_compass_state;
uint8_t mode_reg_addr;
int compass_chip_addr;
int compass_slave_id;
inv_icm20948_compass_state_t compass_state;
} secondary_state;
/* self test */
uint8_t selftest_done;
uint8_t offset_done;
uint8_t gyro_st_data[3];
uint8_t accel_st_data[3];
/* mpu fifo control */
struct fifo_info_t
{
int fifoError;
unsigned char fifo_overflow;
} fifo_info;
/* interface mapping */
unsigned long sStepCounterToBeSubtracted;
unsigned long sOldSteps;
/* data converter */
long s_quat_chip_to_body[4];
/* base driver */
uint8_t sAllowLpEn;
uint8_t s_compass_available;
uint8_t s_proximity_available;
/* base sensor ctrl*/
unsigned short inv_dmp_odr_dividers[37];//INV_SENSOR_NUM_MAX /!\ if the size change
unsigned short inv_dmp_odr_delays[37];//INV_SENSOR_NUM_MAX /!\ if the size change
unsigned short bac_on; // indicates if ANDROID_SENSOR_ACTIVITY_CLASSIFICATON is on
unsigned short pickup;
unsigned short bac_status;
unsigned short b2s_status;
unsigned short flip_pickup_status;
unsigned short inv_sensor_control;
unsigned short inv_sensor_control2;
unsigned long inv_androidSensorsOn_mask[2] ;// Each bit corresponds to a sensor being on
unsigned short inv_androidSensorsOdr_boundaries[51][2];//GENERAL_SENSORS_MAX /!\ if the size change
unsigned char sGmrvIsOn; // indicates if GMRV was requested to be ON by end-user. Once this variable is set, it is either GRV or GMRV which is enabled internally
unsigned short lLastHwSmplrtDividerAcc;
unsigned short lLastHwSmplrtDividerGyr;
unsigned char sBatchMode;
uint8_t header2_count;
char mems_put_to_sleep;
unsigned short smd_status;
unsigned short ped_int_status;
unsigned short bac_request;
uint8_t go_back_lp_when_odr_low; // set to 1 when we forced a switch from LP to LN mode to be able to reach 1kHz ODR, so we will need to go back to LP mode ASAP
unsigned short odr_acc_ms; // ODR in ms requested for ANDROID_SENSOR_ACCELEROMETER
//unsigned short odr_acc_wom_ms; // ODR in ms requested for ANDROID_SENSOR_WOM when using ACC
unsigned short odr_racc_ms; // ODR in ms requested for ANDROID_SENSOR_RAW_ACCELEROMETER
unsigned short odr_gyr_ms; // ODR in ms requested for ANDROID_SENSOR_GYROSCOPE_UNCALIBRATED
unsigned short odr_rgyr_ms; // ODR in ms requested for ANDROID_SENSOR_RAW_GYROSCOPE
int bias[9];// dmp bias [0-2]:acc,[3-5]:gyr,[6-8]:mag
/* Icm20948Fifo usage */
signed char mounting_matrix[9];
signed char mounting_matrix_secondary_compass[9];
long soft_iron_matrix[9];
uint8_t skip_sample[INV_ICM20948_SENSOR_MAX+1];
uint64_t timestamp[INV_ICM20948_SENSOR_MAX+1];
uint8_t sFirstBatch[INV_ICM20948_SENSOR_MAX+1];
sensor_type_icm20948_t sensorlist[INV_ICM20948_SENSOR_MAX+1];
unsigned short saved_count;
/* Icm20948Transport*/
unsigned char reg;
unsigned char lastBank;
unsigned char lLastBankSelected;
/* augmented sensors*/
unsigned short sGravityOdrMs;
unsigned short sGrvOdrMs;
unsigned short sLinAccOdrMs;
unsigned short sGravityWuOdrMs;
unsigned short sGrvWuOdrMs;
unsigned short sLinAccWuOdrMs;
unsigned short sRvOdrMs;
unsigned short sOriOdrMs;
unsigned short sRvWuOdrMs;
unsigned short sOriWuOdrMs;
/* Icm20649Setup */
short set_accuracy;
int new_accuracy;
} inv_icm20948_t;
这是一个较为庞大的结构体，其中囊括了各种功能。而此结构体的第一个成员正是struct inv_icm20948_serif serif。
回到inv_icm20948_reset_states函数中：
/** @brief Reset and initialize driver states
* @param[in] s handle to driver states structure
*/
static inline void inv_icm20948_reset_states(struct inv_icm20948 * s,
const struct inv_icm20948_serif * serif)
{
assert(icm20948_instance == 0);
memset(s, 0, sizeof(*s));
s->serif = *serif;
icm20948_instance = s;
}inv_icm20948_reset_states函数的代码比较简单，先是将第1个参数的全部成员清零。这里，由于第1个参数对应的实参icm_device是全局变量，系统已经自动清零了，因此实际上这一句有没有都可以。如果有传入的实参为局部变量的情况，那么这一句就有用了。
接下来，就是将struct inv_icm20948对象的第一个成员struct inv_icm20948_serif serif赋值为main函数中新建的那个inv_icm20948_serif serif。注意这里是值传递，也就是两者并不指向同一段内存。
接下来将第1个参数赋给icm20948_instance。icm20948_instance也是一个全局变量，在EMD-Core\sources\Invn\Devices\Drivers\ICM20948\Icm20948Transport.c中，如下：
struct inv_icm20948 * icm20948_instance;这里就和inv_icm20948_reset_states函数的第1行代码对应起来了。
assert(icm20948_instance == 0);调用inv_icm20948_reset_states函数的时候必须要求第1个参数对应的实参为空。由于struct inv_icm20948 * icm20948_instance为全局变量，因此系统会将其设置为0即空。
至此，main函数第2段代码片段的前一个函数inv_icm20948_reset_states就讲解完了。下一回讲解后一个函数inv_icm20948_register_aux_compass。
