program is blocked at system_init, UART? or I2C?

HI, Dialog,
My I2C device has two part of program: initialiazing / operation.
I put it in project hrp_sensor.
The initialazing code is at function system_init: (RETARGET has been defined)
//----------------------------------------
static void system_init( void *pvParameters )
{
OS_TASK handle;
unsigned char d;
i2c_device dev;

#if defined CONFIG_RETARGET
extern void retarget_init(void);
# endif
....
....
#if defined CONFIG_RETARGET
retarget_init();
# endif

printf("BLE hrp demo" NEWLINE);

dev = ad_i2c_open(MAX30100); //---- I2C device initializing ----------------------

MAX30100_reset(dev);
d = MAX30100_read(dev,MAX30100_PART_ID);
printf(NEWLINE "PART ID=%02x",d); //--- this line works fine, and program is blocked at here
d = MAX30100_read(dev,MAX30100_REVISION_ID);
printf(NEWLINE "Revision ID=%02x",d);

// Set LED current
MAX30100_setLEDs(dev,i11, i8);
....
....
//----------------------------------------------------------------

When DA14681 runs, my UART terminal shows like this:
//------------------------------
'''' BLE hrp demo
PART ID =11
//------------------------------
the next output 'Revision ID=05' will go on when you connect this BLE device by mobile.
发生了什么在background?
How to improve my code?
Note: my I2C device is controlled by function ad_i2c_read(), ad_i2c_write() --- they works in async mode.

Thanks