AN4650 datasheet(85/102 Pages) STMICROELECTRONICS

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AN4650

First-in first-out (FIFO) buffer

102

Follow these steps for Continuous-to-FIFO mode configuration (if the

accelerometer/gyroscope data-ready is used as the FIFO trigger):

Configure one of the events as previously described;

Choose the decimation factor for each sensor through the decimation bits in the

FIFO_CTRL3 and FIFO_CTRL4 registers (see Section 8.3 for details);

Choose the FIFO ODR through the ODR_FIFO_[3:0] bits in the FIFO_CTRL5 register;

Set the FIFO_MODE_[2:0] bits in the FIFO_CTRL5 register to 011b to enable FIFO

Continuous-to-FIFO mode.

In Continuous-to-FIFO mode the FIFO buffer continues filling; when the buffer is full, the

FIFO_FULL bit is set high.

If the STOP_ON_FTH bit of the CTRL4_C register is set to 1, the FIFO size is limited to the

value of the FTH_[11:0] bits in the FIFO_CTRL1 and FIFO_CTRL2 registers: in this case,

the FIFO_FULL bit of the FIFO_STATUS2 register is set high when the number of samples

in FIFO will reach or exceed the FTH_[11:0] value on the next FIFO write operation.

When the trigger event occurs, two different cases can be observed:

If the FIFO buffer is already full (FIFO_FULL = 1), it stops collecting data at the first

sample after the event trigger. The FIFO content is composed of the samples collected

before the event.

If FIFO buffer is not full yet (initial transient), it continues filling until it becomes full

(FIFO_FULL = 1) and then, if the trigger is still present, it stops collecting data.

Continuous-to-FIFO can be used in order to analyze the history of the samples which have

generated an interrupt; the standard operation is to read the FIFO content when the FIFO

mode is triggered and the FIFO buffer is full and stopped.

8.2.5

Bypass-to-Continuous mode

This mode is a combination of the Bypass and Continuous modes previously described. In

Bypass-to-Continuous mode, the FIFO buffer starts operating in Bypass mode and switches

to Continuous mode when a trigger condition occurs.

The event condition can be one of the following:



Significant Motion: event detection has to be configured and the INT1_SIG_MOT bit of

the INT1_CTRL register has to be set to 1;



Tilt: event detection has to be configured and the INT2_TILT bit of the MD2_CFG



Step detection: event detection has to be configured and the INT1_STEP_DETECTOR

bit of the INT1_CTRL register has to be set to 1;



Single tap: event detection has to be configured and the INT2_SINGLE_TAP bit of

MD2_CFG register has to be set to 1;



Double tap: event detection has to be configured and the INT2_DOUBLE_TAP bit of

the MD2_CFG register has to be set to 1;



Free-fall: event detection has to be configured and the INT2_FF bit of the MD2_CFG



Wake-up: event detection has to be configured and the INT2_WU bit of the MD2_CFG



6D: event detection has to be configured and the INT2_6D bit of the MD2_CFG register

has to be set to 1.

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