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?

[SaeedZadeh]

Hi Naeem,

I appreciate your consideration.

This project involves receiving data from the IMU and ADC and transferring it via BLE. The IMU has two interrupts: INT1 for FIFO ready and INT2 for special events like taps.

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. This is with the first overlay-debug.conf configuration.

I followed Edvin's advice and changed the overlay-debug.conf. After the IMU initialization, neither INT1 nor INT2 triggered, and the IMU shut down.

CONFIG_LOG=y
CONFIG_LOG_MODE_DEFERRED=n
CONFIG_LOG_MODE_IMMEDIATE=y
CONFIG_USE_SEGGER_RTT=y
CONFIG_CONSOLE=y
CONFIG_UART_CONSOLE=n
CONFIG_RTT_CONSOLE=y
CONFIG_LOG_BACKEND_RTT=y
CONFIG_LOG_BACKEND_UART=n
CONFIG_LOG_PRINTK=n

# Troubleshooting
CONFIG_ASSERT=y
CONFIG_RESET_ON_FATAL_ERROR=n


CONFIG_MAIN_THREAD_PRIORITY=8

I then applied the following configuration, which allows INT1 to trigger on time even when RTT is disconnected. However, INT2 does not trigger and remains inactive.

CONFIG_LOG=y
CONFIG_LOG_MODE_DEFERRED=n
CONFIG_LOG_MODE_IMMEDIATE=y
CONFIG_USE_SEGGER_RTT=y
CONFIG_CONSOLE=y
CONFIG_UART_CONSOLE=n
CONFIG_RTT_CONSOLE=n
CONFIG_LOG_BACKEND_RTT=n
CONFIG_LOG_BACKEND_UART=n
CONFIG_LOG_PRINTK=n

# Troubleshooting
CONFIG_ASSERT=y
CONFIG_RESET_ON_FATAL_ERROR=n


CONFIG_MAIN_THREAD_PRIORITY=8

I don't believe the issue lies with the IMU itself, as the only changes I made were to the overlay-debug.conf.

You canjust download the latest file that I uploaded here and build. Please note that the SDK version is v2.5.2.

Thank you,

[Naeem Maroof]

Are there any special things with the INT2?

I see that there are 3 modes in which  sensor could be connected,

and the role of INT1 is same for all the modes, but INT2 is different.

I have not used this sensor, but just pointing if that is something to look at.

[SaeedZadeh]

The problem doesn't seem to be with the sensor configuration since I haven't changed anything on the sensor side and get the proper result while the RTT is connected. However, changing the overlay_debug alters the sensor's behavior. I believe there might be an issue with my nRF configuration. What are your thoughts?

Thsnk you,

[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):

[SaeedZadeh]

Hi Naeem,

Thank you for your consideration.

Could you please clarify what the "overlay-debug.conf" configuration entails? As I mentioned earlier, in a setup where everything functions correctly, as you indicated, the INT2 of the IMU does not trigger. However, in a setup where the timing and RTT are problematic, INT2 triggers perfectly. I'm trying to understand the relationship between these configurations. 

In the following configuration, the sensor's part works perfectly, but the timing is correct while RTT is connected:

# Debug configuration

# Logging
CONFIG_LOG=y
CONFIG_LOG_MODE_DEFERRED=n
CONFIG_LOG_MODE_IMMEDIATE=y
CONFIG_USE_SEGGER_RTT=y
CONFIG_CONSOLE=y
CONFIG_UART_CONSOLE=n
CONFIG_RTT_CONSOLE=n
CONFIG_LOG_BACKEND_RTT=n
CONFIG_LOG_BACKEND_UART=n
CONFIG_LOG_PRINTK=n

# Troubleshooting
CONFIG_ASSERT=y
CONFIG_RESET_ON_FATAL_ERROR=n


CONFIG_MAIN_THREAD_PRIORITY=8

Thank you.

[Naeem Maroof]

Hi Sid,

I have this in the overlay-debug conf:

# Debug configuration

# Logging
CONFIG_LOG=y
CONFIG_LOG_MODE_DEFERRED=n
CONFIG_LOG_MODE_IMMEDIATE=y
CONFIG_USE_SEGGER_RTT=y
CONFIG_CONSOLE=y
CONFIG_UART_CONSOLE=n
CONFIG_RTT_CONSOLE=y
CONFIG_LOG_BACKEND_RTT=y
CONFIG_LOG_BACKEND_UART=n
CONFIG_LOG_PRINTK=n

# Troubleshooting
CONFIG_ASSERT=y
CONFIG_RESET_ON_FATAL_ERROR=n

and now I can see what you mean.

When I connect the RTT, I see logs on the 52DK side coming ~20ms apart

and without the RTT I see logs on the 52DK side coming ~200ms apart

I am not sure what is causing this.

Where have you set the timing parameters that captures samples after fix amount of time? Is it fixed in terms of clock cycles or in terms of time units?

I also see that ble_send is called in different function, can they (or their callbacks) be somehow dependent upon some other things, like I see that button handler is one that submits imu tap and imu data works.