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]

Ok, thanks for your quick response. I''ll wait with opening the OLS until I got your results.

If you need support tomorrow, I'm available basically the whole day, so I could give you support here, over E-Mail, or in a phone call.

Regards, Loris

[Eleon BORLINI]

Hi @Loris Wyss​ , what I can see following this procedure is that I can see the interrupt on INT1 (instead of on INT2 as you reported.. I tried to trigger the shot on the INT2 signal but it is always at 0V, see the blue line), and this interrupt is flickering in DURATION of about the quantity you reported. This could cause the jitter. But the distance between the rising edge of two consecutive interrupt pulses seems the same (cursor measure of 15.60ms)...

Single shot screen:

Multiple shots screen:

Did you set the interrupt duration (for example in the INT_DUR (33h) or in the WAKE_UP_DUR (35h) registers?

Regards

[Loris Wyss]

Hi @Eleon BORLINI​ 

Thanks for your feedback, You're right I mixed up the interrupt pins in my instruction-post.

It's strange that you don't see the Jitter on the rising edges. I just tried it again and I can still see the exact same behaviour as described/shown in the first post.

Could you try zooming in at the rising edge, which follows the one you triggered on? If you let the measurement run, you should be able to see that the rising edge is jumping between two positions...

[Eleon BORLINI]

well... after some run I can see the jitter too... Since I didn't see it with the standard STEVAL-MKI109V3 + STEVAL-MKI179V1 tool, to understand if it is a device-related or custom board / FW - related issue I should de-solder it and check it at bench... But I cannot guarantee I'll do it in the short term... :( Regards

[Loris Wyss]

Ok, well that's already some good news!

Could you share the configuration you used with the eval-kits here? Then I could configure the one on my PCB in the same way and check, if the jitter is still here.

From your experience, how fast do I get results, when I open an OLS-request?

Regards, Loris

Edit:

I've just seen you mentioned the Interrupt duration-Registers. I have not set them, because I haven't seen anything related to the Threshold-interrupt being mentioned in the respective register desriptions in the datasheet.

[Loris Wyss]

@Eleon BORLINI​ 

I just discovered something really interesting:

I think it has to do with the SPI readout speed.

As I have already written some time ago, I read data at 7.5MBit/s. When playing around with the prescaler values I found out, that the Issue is gone at 1.875 MBit/s. With half (937.5 KBit/s) or double (3.75 MBit/s) of that value, the interrupt is jittering again!

I suspected from the beginning, that the SPI readout speed might have something to do with it, but this specific behauviour is not what I expected. I mean, why is there a problem with a higher speed (Which is still lower than the specified max. Speed of 10 MBit/s)?

Maybe, you can test that as well with the Eval-Kits?

[Eleon BORLINI]

Hi @Loris Wyss​ , this is an interesting thing. I suspected a correlation with the SPI speed too. I used the examples on Github at this link. Do you think you can manage the issue reducing the SPI speed? Regards

[Loris Wyss]

Hi @Eleon BORLINI​ 

Thanks for the Link.

I think, adjusting the SPI speed might solve the problem in this specific case, but we use the sensor with different configurations and uCs in our company and we have to be sure for all this cases, that this issue doesn't occur.

To get further support, I opened an OLS request.

I thank you for your efforts. I will get back to you when I know, where the PCB has to be shipped to.

Regards, Loris

[Eleon BORLINI]

Thanks for your long patience too... and please let me know the further results.

Best regards, Eleon

[Loris Wyss]

Hi @Eleon BORLINI​ 

My OLS case (https://community.st.com/s/case/5003W000002fTVZQA2) is now supported by Mr. Martin Polacek.

Did he contact you?

Do you still have the PCB I sent you? If so, I think it would make sense to ship this to Mr. Polacek.

Could you please quickly sum up, what the current status is?

Thanks and Regards,

Loris