J-Link RTT Viewer application receives logs with high latency

RE: J-Link RTT Viewer application receives logs with high latency

Håkon Alseth — Mon, 27 Jul 2020 12:27:16 GMT

Hi,

Unfortunately, you cannot log immediately when using bluetooth, as this will introduce interrupt latency (and thus; might affect the runtime behavior of the BLE stack):

https://github.com/nrfconnect/sdk-zephyr/blob/master/subsys/bluetooth/common/dummy.c#L32-L40

Are you only using printk() to get your logging output, and do not rely on the LOG module? If yes, then you can disable LOG (CONFIG_LOG=n), then use RTT for printk() operations. This shall be printed without a scheduler in the background.

Kind regards,

Håkon

RE: J-Link RTT Viewer application receives logs with high latency

RAlexeev — Fri, 24 Jul 2020 14:05:59 GMT

Thank you, Simon, for suggestions. I tried to set an option CONFIG_LOG_IMMEDIATE

In the case of nRF52840 DK it didn't work because of assertion error:

devzone.nordicsemi.com/.../CONFIG_5F00_LOG_5F00_IMMEDIATE_5F00_error.txt

In the case of nRF5340 PDK I didn't notice any differences in log output speed with CONFIG_LOG_IMMEDIATE or without this option. The same output of printk() function to UART works about immediately, but I see the same log output in J-Link RTT Viewer after a significant delay.

I will read the recommended blogs and try again to cope with slow log output speed.

RE: J-Link RTT Viewer application receives logs with high latency

Simon — Fri, 24 Jul 2020 12:53:39 GMT

If you want faster logging/processing you could enable CONFIG_LOG_IMMEDIATE, however, it has some impacts on the performance:

"It impacts performance of the system since time consuming operations are performed in the context of the log entry (e.g. high priority interrupt)."

These blogs may also be insightful:

If you want to decrease the amount of dropped messages, you could try to follow the tips by Einar in this ticket. Even though it is for the nRF5 SDK and not NCS, I think the tips should still be relevant for you.

Best regards,

Simon