"usb_cdc_acm: Ring buffer full, drain buffer" repeats on boot

[ZacMid007]

I'm developing code for the xiao_ble board in nRF Connect using Visual Studio, currently working with the ble light_switch example. I'm using the logger module rather than eg printk() as for whatever reason printk() doesn't come through the USB connector (not the point of this question). However, every time I boot the board, I see the following:

The number of messages dropped ranges anywhere from 10 to over 100. I observed these before I enabled the logger module, ie they were already present before I modified any code in the example. I added the following lines to my proj.conf, but this didn't fix anything:

Is there a simple fix? Regular logging works fine after all the "Ring buffer full" messages have finished.

[Håkon Alseth]

Hi,

 

Are you sending and receiving alot of data when this happens?

Can you share a bit more information on how you're using the CDC_ACM module? for instance your event_handler.

 

Kind regards,

Håkon

[ZacMid007]

Hi,

I am not sending any data (the issue persists even when all print/log statements are removed), nor did I include the CDC_ACM module; whatever this is, it's occurring by default within the nrf/samples/bluetooth/mesh/light_switch example

[Håkon Alseth]

Hi,

 

The board "xiao_ble" will by default use USB CDC_ACM for logging and printing on console:

https://github.com/nrfconnect/sdk-zephyr/blob/v3.2.99-ncs2/boards/arm/xiao_ble/xiao_ble.dts#L18-L22

What you can do is to try to adjust the ring buf size:

CONFIG_USB_CDC_ACM_RINGBUF_SIZE=4096

 

Do you get anything else at all on your log interface, or is this the only thing that is printed? Do you see this with other samples, or only the bluetooht/mesh/light_switch sample?

 

Kind regards,

Håkon

[ZacMid007]

If I don't use any other log statements, that screenshot is all that appears on the interface, yes. I tried another example, the mesh chat one, and do not see the same thing:

However, going back to the light_switch example and changing the ring buf size to 4096, now I see this on boot (but not every time, maybe 1 in 3 times when I boot the device):

[Håkon Alseth]

Hi,

 

ZacMid007 said:

However, going back to the light_switch example and changing the ring buf size to 4096, now I see this on boot (but not every time, maybe 1 in 3 times when I boot the device):

Good to hear that the issue is improving.

"device not ready" means that the port hasn't been opened from the PC yet. The logger module will buffer a given amount of strings, which is the reason why you're getting those error prints when it finally has opened up the port. Other log messages should appear, and if you want printk to be processed by the log module, you can set "CONFIG_LOG_PRINTK=y"

 

Kind regards,

Håkon

[ZacMid007]

Other log messages do indeed appear once the port is open, I'm just confused as to why so many strings seem to be attempted to print at boot, as I am not logging anything and cannot see where in the code that volume of messages could be coming from

[Håkon Alseth]

Hi,

 

It highly depends on which modules are enabled in your firmware, and the level of the logger module.

Informational logs can fill up the log queue quite quickly, especially when the backend isn't yet ready.

 

Kind regards,

Håkon