Adafruit feather nRF52840 development board printf to USB

[zazas321]

Hello. I have recently ordered a few official samples from Nordic as well as few small samples from Adafruit.

I have realized that Adafruit Feather nRF52840 does not have built in USB->UART converter so that makes it very difficult to troubleshoot the code (not able to do any printf statements directly to the console or any serial terminal). The only way to debug this is to connect the J-Link debugger which is ok but not very convenient when you need to quickly check something.

I have tried to run the zephyr/samples/subsys/usb/cdc_acm and also zephyr_samples/subsys/usb/console but could not get any printf statements to print anything to serial console. I have tried both of these sample projects on Adafruit Feather nRF52840 board as well as nRF8540DK nRF52840 development board from nordic.

Could someone point me in the right direction how can I achieve this? Thanks in advance.

[Raoul]

Hi Lukas,

Could someone point me in the right direction how can I achieve this?

May I point you to the following two cases, to begin with?

 printk on USB port nrf dongle 

 How to config Zephyr if want to output debug message through USB port on nrf52840 dongle

Alternatively, if you have a DK lying around, you might also be able to pipe data over the SWD pins (if you have the connector for that) through your DK, by configuring printk/logging to occur over RTT.

Let me know if that doesn't get you anywhere!

Apologies for the delay and hurried answer.

Best regards,

Raoul

[zazas321]

I have managed to get console over usb sample project to print to serial terminal. There was one crucial step missing in the instructions or documentation.

The sample project will only work if the serial terminal has flow control enabled

By default, I never use flow control for any of the devices that I use serial communication hence I thought I did not need it.

I have decided to change it just for curiosity and I started seeing messages on the console right away:

It would probably be good idea to include this in README as it is not obvious that you have enable flow control

If you do not want to use flow control, you can just comment out the following code in the console sample project:

	 while (!dtr) {
	 	uart_line_ctrl_get(dev, UART_LINE_CTRL_DTR, &dtr);
	 	/* Give CPU resources to low priority threads. */
	 	k_sleep(K_MSEC(100));
	 }

Moreover, I would like to understand what are the differences between console and cdc_acm projects.  By adding 

/ {
	chosen {
		zephyr,console = &cdc_acm_uart0;
	};
};

I can also get the cdc_acm project to print to console. 

cdc_acm seems to be quite a bit more complex compared to console sample project. Could you help me understand what are the differences?

[Raoul]

Hi Lukas,

Thanks a lot for sharing your findings! I will pass your notes on to the docs team as feedback.

Regarding those differences between the two apps, I'll take a closer look and get back to you soon.

Best regards,

Raoul

[Simonr]

Hi Lukas

Raoul asked me to take a look at this case.

The Console over CDC ACM UART sample is just a simple "Hello World" type sample to show the required config options for a console output via the CDC ACM UART. The USB CDC ACM sample is more a full demonstration of the CDC ACM driver provided by Zephyr, and echoes received data back to the same port. Did you have anything more specific in mind regarding the difference(s) between the two samples?

As for the flow control being documented. The recommended console settings are documented in the working with nRF52 series getting started guide, as the Zephyr samples are not specific to the nRF series, and HW setup will differ between the chips used.

Best regards,

Simon

[zazas321]

Thanks for clarifying. It is a little bit more clear now :)