Issue with IMU Sensor (LSM6DSV16X) Sample Rate in Sensor Hub Mode

[SaeedZadeh]

I am using an IMU sensor in sensor hub mode (LSM6DSV16X, LIS2MDL) with the FIFO interrupt interval set at 30 Hz. The data is sent over BLE. It works perfectly when using RTT, but when I disable debug mode, the sample rate drops to around 1 Hz.

Could someone please help me resolve this issue?

Thank you.

[SaeedZadeh]

Thank you for your reply. When the IMU's FIFO is full, an interrupt will occur on the interrupt pin. The interrupt rate will decrease to 1 Hz as if something changes or is missed when I disable the RTT configuration.

[Edvin]

So what triggers the IMU readings in the first place? Do you have a timer set up at 30Hz or something?

What HW are you running this on? nRF5340DK? Or do you have a custom board?

[Naeem Maroof]

But this:

SaeedZadeh said:

INT1 should trigger approximately every 10 ms, which it does when the RTT is connected. However, when I disconnect RTT, the trigger time significantly increases to around 170 ms.

does not make sense then, because the RTT is on the DK / MCU side, and the INT1 is generated by sensor which is already configured, right? How changing (logging) behavior can impact the sensor firing interrupt? I do not know about this sensor configurations. 

Can you print system time when interrupt is generated by the sensor, and then from there we see how much time it is taking between interrupts, so we do not see the logging time but rather interrupt firing time.

Can you show the changes you made in the overlay?

[SaeedZadeh]

Thank you for your reply. 

Naeem Maroof said:

does not make sense then, because the RTT is on the DK / MCU side, and the INT1 is generated by sensor which is already configured, right? How changing (logging) behavior can impact the sensor firing interrupt? I do not know about this sensor configurations. 

This is why I am confused, as I don't change anything in the main code or IMU, but I change the overlay_debug and have a different result.

Naeem Maroof said:

Can you print system time when interrupt is generated by the sensor, and then from there we see how much time it is taking between interrupts, so we do not see the logging time but rather interrupt firing time.

Please take a look at the image below. You'll notice that INT1 triggers a ~10 ms interrupt, while INT2 remains high, instead of being low and transitioning to high when an event occurs.

Naeem Maroof said:

Can you show the changes you made in the overlay?

I changed the following line to "n" and got the above result. 

CONFIG_RTT_CONSOLE=y
CONFIG_LOG_BACKEND_RTT=y

Best,

Saeed

[SaeedZadeh]

Hi Naeem,

Have you had a look at my reply by any chance? Please let me know if you need any further information.

Bests,

[Naeem Maroof]

Hi Sid,

Apologies for the delayed response due to high work load.

I have used the 2 zip files that you uploaded last time (one for the NRF52DK and the other for the 5340DK)

I am using those projects as it is (without anything changing):

I can see the output on the console connected to the NRF52DK that is receiving BLE data from the NRF5340DK. I can see that LED and ADC data is printed.

Next, on the 5340DK, in the main code, I put timestamp when we are setting up the tx_ble_buffer.

I can see that LED and ADC data is received after 20ms, which matches with what you were saying and expecting.

Then I connected RTT on 5340DK (using the VS Code Extension-->Connected devices-->5340DK-->RTT)

I can see that the Interface MCU led is blinking fast, which is showing the RTT connection.

I can still see on the output that the LED and ADC data is received after 20ms. Snapshot attached where RTT is connected:

[Naeem Maroof]

As I said I did not change anything (except that timestamping in the ble-tx-buffer),

I am also attaching the console output of 5340DK (which is blank):