LSM6DSM Datasheet, PDF (34/113 Pages) STMicroelectronics – always-on 3D accelerometer and 3D gyroscope

Functionality
LSM6DSM
5.5
5.5.1
FIFO
The presence of a FIFO allows consistent power saving for the system since the host
processor does not need continuously poll data from the sensor, but it can wake up only
when needed and burst the significant data out from the FIFO.
The LSM6DSM embeds 4 kbytes data FIFO to store the following data:
 gyroscope
 accelerometer
 external sensors
 step counter and timestamp
 temperature
Writing data in the FIFO can be configured to be triggered by the:
 accelerometer/gyroscope data-ready signal; in which case the ODR must be lower
than or equal to both the accelerometer and gyroscope ODRs;
 sensor hub data-ready signal;
 step detection signal.
In addition, each data can be stored at a decimated data rate compared to FIFO ODR and it
is configurable by the user, setting the FIFO_CTRL3 (08h) and FIFO_CTRL4 (09h)
registers. The available decimation factors are 2, 3, 4, 8, 16, 32.
The programmable FIFO threshold can be set in FIFO_CTRL1 (06h) and FIFO_CTRL2
(07h) using the FTH [11:0] bits.
To monitor the FIFO status, dedicated registers (FIFO_STATUS1 (3Ah), FIFO_STATUS2
(3Bh), FIFO_STATUS3 (3Ch), FIFO_STATUS4 (3Dh)) can be read to detect FIFO overrun
events, FIFO full status, FIFO empty status, FIFO threshold status and the number of
unread samples stored in the FIFO. To generate dedicated interrupts on the INT1 and INT2
pads of these status events, the configuration can be set in INT1_CTRL (0Dh) and
INT2_CTRL (0Eh).
The FIFO buffer can be configured according to five different modes:
 Bypass mode
 FIFO mode
 Continuous mode
 Continuous-to-FIFO mode
 Bypass-to-continuous mode
Each mode is selected by the FIFO_MODE_[2:0] bits in the FIFO_CTRL5 (0Ah) register. To
guarantee the correct acquisition of data during the switching into and out of FIFO mode,
the first sample acquired must be discarded.
Bypass mode
In Bypass mode (FIFO_CTRL5 (0Ah) (FIFO_MODE_[2:0] = 000), the FIFO is not
operational and it remains empty.
Bypass mode is also used to reset the FIFO when in FIFO mode.
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