LIS2DW12: FIFO-Threshold-Interrupt Jitters at 1.6kHz

[Loris Wyss]

Hello ST-Community!

When I'm using the LIS2DW12 at ODR=1.6kHz, the Interrupt for reaching the FIFO-Threshold is jittering with 1/ODR, but only if the threshold is greater than 12. If it's less or equal, everything is working fine.

The buffer-Mode is set to FIFO-Mode, but this behaviour also occurs in Continous-Mode.

The Power-Mode is set to High-Performance/Low-Noise.

The Interrupt is routed to the INT1-Pin

The two images show the rising edge on the pin INT1. The time between the two cursors "a" and "b" is 624us (almost 625us), which would equal to 1/ODR (1/1600 = 625E-6)

As written, this only happens if ODR is set to 1.6kHz and the FIFO-Threshold is greater than 12.

Does anyone have some further informations regarding this issue?

Thanks in advance for your answers!

Greetings,

Loris

[Loris Wyss]

Hi Eleon

The PCB was shipped today, so it will probably arrive by the end of the week.

If you have any questions, just let me know.

Regards,

Loris

[Eleon BORLINI]

​Just at the beginning of the Christmas holidays ;) ok, let's see what we can do

Regards

[Loris Wyss]

Yeah, I know.

Timing at it's best... ;)

Thanks for your efforts!

[Eleon BORLINI]

Hi Loris, just received your board, thank you for your effort. I have some other question about the issue you are facing:

• you are acquiring data at 1.6kHz, filling the FIFO at that speed, and when the FIFO is full you read the data together, checking the interrupt and its jitter. At which speed do you read the data (e.g. SPI 1Mbit)?
• are you using the FIFO stop filling mode (FMode[2:0] 001 in FIFO_CTRL (2Eh))? There can be the possibility that, if this mode is not selected, the FIFO updates while you are emptying it and the interrupt raises not after 12 new samples but after only 11 samples (the 1st samples already in FIFO during you are reading it, so the interrupt raises only after ODR*11 seconds). I don't know if I made myself be understood...
• can you try to do the same test at higher SPI speeds and/or lower ODR, and maybe with the STOP filling enabled, and check in time if the jitter is still there?

Regards

[Loris Wyss]

Hi Eleon

Regarding speeds:

• The SPI clock speed was set to 7.5 MHz
• Due to the clock configuration in the STM32, I can't increase the SPI speed and also decreasing it doesn't help
• When decreasing the ODR to 800 MHz or lower, the Jitter is gone as well

The Sensor is running in FIFO-Mode (FMode[2:0] 001), so that doesn't solve the problem. But as far as I understand the Datasheet, in FIFO Mode the Sensor stops collecting Data as soon as there are 32 unread samples in the FIFO. But for me It's not really clear if this happens as well when the FIFO Threshold is reached (In my case 24).

I hope this helped you.

Regards,

Loris

[Loris Wyss]

Hi @Eleon BORLINI​ 

Have you got any Updates for me?

Were you able to put the board in operation?

Thanks and Regards

Loris

[Eleon BORLINI]

Hi @Loris Wyss​ , unfortunately not yet, or, better, I'm still not able to reproduce the jitter failure...

Let me check again other configurations before coming back to you

Regards

[Loris Wyss]

Ok, thanks for the update.

Just for clarity: Can you see the described behaviour with the Hardware i sent you?

Regards

[Loris Wyss]

Hi @Eleon BORLINI​ 

Have you found out anything regarding this Issue?

And have you been able to reproduce the described behaviour with the PCB i sent you?

Regards

[Eleon BORLINI]

Hi @Loris Wyss​ , I'm very sorry to come back to you without a news on your PCB... But I can ship back it to you, if you want. Btw, can you please check if your issue is somehow related to this other thread? Regards