接前一篇文章：ICM20948 DMP代码详解（30）
本回继续往下解析inv_icm20948_initialize_lower_driver函数的后续代码。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：
cpp
/** 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 variable
s->sAllowLpEn = 1;
s->s_compass_available = 0;
// ICM20948 do not support the proximity sensor for the moment.
// s_proximity_available variable is nerver changes
s->s_proximity_available = 0;
// Set varialbes to default values
memset(&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 mode
result |= 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;
else
s->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;
else
s->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 size
result |= 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 Interrupt
data = 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 fix
inv_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 B2S
dmp_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：
cpp
// 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.两个函数分别来看。
- inv_icm20948_set_gyro_divider函数
inv_icm20948_set_gyro_divider函数在EMD-Core\sources\Invn\Devices\Drivers\ICM20948\Icm20948DataBaseDriver.c中，代码如下：
cpp
int inv_icm20948_set_gyro_divider(struct inv_icm20948 *s, unsigned char div)
{
s->base_state.gyro_div = div;
return inv_icm20948_write_mems_reg(s, REG_GYRO_SMPLRT_DIV, 1, &div);
}REG_GYRO_SMPLRT_DIV宏在EMD-Core\sources\Invn\Devices\Drivers\ICM20948\Icm20948Defs.h中，定义如下：
cpp
#define REG_GYRO_SMPLRT_DIV (BANK_2 | 0x00)对应芯片手册的以下内容：
正如代码注释所说，这段代码的意思是初始化设置陀螺仪的采样分频值即采样率。具体值为：1125Hz/19+1 = 56Hz。同时，设置s->base_state.gyro_div为实参值FIFO_DIVIDER。FIFO_DIVIDER宏在EMD-Core\sources\Invn\Devices\Drivers\ICM20948\Icm20948Defs.h中定义，如下：
cpp
#define FIFO_DIVIDER 19- inv_icm20948_set_accel_divider函数
inv_icm20948_set_accel_divider函数也在EMD-Core\sources\Invn\Devices\Drivers\ICM20948\Icm20948DataBaseDriver.c中，代码如下：
cpp
int inv_icm20948_set_accel_divider(struct inv_icm20948 *s, short div)
{
unsigned char data[2] = {0};
s->base_state.accel_div = div;
data[0] = (unsigned char)(div >> 8);
data[1] = (unsigned char)(div & 0xff);
return inv_icm20948_write_mems_reg(s, REG_ACCEL_SMPLRT_DIV_1, 2, data);
}REG_ACCEL_SMPLRT_DIV_1宏在EMD-Core\sources\Invn\Devices\Drivers\ICM20948\Icm20948Defs.h中，定义如下：
cpp
#define REG_ACCEL_SMPLRT_DIV_1 (BANK_2 | 0x10)
#define REG_ACCEL_SMPLRT_DIV_2 (BANK_2 | 0x11)对应芯片手册的以下内容：
正如代码注释所说，这段代码的意思是初始化设置加速度计的采样分频值即采样率。具体值为：1125Hz/19+1 = 56Hz。同时，设置s->base_state.accel_div为实参值FIFO_DIVIDER。
除了以上两个函数外，还设置了struct inv_icm20948 *s成员：
cpp
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.综合来看，这段代码的意思就是设置陀螺仪和加速度计的采样率，同时记录值到相关成员。
下一回继续解析inv_icm20948_initialize_lower_driver函数中的后续代码。