mma8652 fifo trigger mode behaviour

[meirsudry]

Hi

i'd like to use FIFO in trigger mode. i'd like to record 10 samples before transient event and the rest (22 samples) after.

i also want the transient event to wake up the device and start sampling at higher rate (800Hz when awake and 50 Hz when sleep).

i saw in the datasheet that FIFO is flushed whenever the DR is switched due to sleep-wake transition. is that includes working with FIFO in trigger mode?

if yes, does it means there is no way to use DR higher than 50 Hz in FIFO trigger mode?

thanks

SUDRY

[TomasVaverka · Accepted solution]

Hi Meir,

I do apologize for this late reply, I had to discuss it with the design team.

So, according to the specification, the FIFO is flushed from sleep to wake transition. The aim being to not save into the FIFO data at different ODR. This includes the FIFO in trigger mode.

But you can trigger the FIFO at any ODR. The triggers are Trig_TRANS, Trig_LNDPRT, Trig_PULSE and Trig_FF_MT (TRIG_CFG reg 0x0A) and are not related to ODR.

Please let me know if you need any further clarification.

Regards,

Tomas

PS: If my answer helps to solve your question, please mark it as "Correct". Thank you.

[meirsudry]

Hi Tomas thanks for the reply. if I got you correct, FIFO trigger mode is irrelevant if sleep mode is enabled. While sensor is in awake mode any of available ODRs can be used. if sleep mode is used, FIFO is flushed in the transition. If I use FIFO interrupt, 32 samples available are all samples that were taken after the selected FIFO trigger event. thanks again Meir