Using USB as virtual com as log with zephyr

[Serafino Convertini]

Hi to all,

I'm developing a beacon application on the nRF52840-DK starting from the example that I found in the VS Code (Zephyr).

I'm designing a custom board with only the nRF onboard (without the interface MCU).

If I insert a USB cable in the USB connector of the nRF micro I cannot see any virtual COM on my PC.

How could I use the USB peripheral of the nRF micro as virtual COM for logging purpose in the Zephyr OS?

Thanks in advance.

[Jared]

Hi,

You can use the USB CDC-Sample as reference,

regards

Jared 

[Serafino Convertini]

Hi,

I tried to build the example "zephyr\samples\subsys\usb\cdc_acm", and I inserted at the end of the code (before return 0) this snippet

while(true){
	LOG_INF("Hello World\n");
	/* Wait 100ms for the host to do all settings */
	k_msleep(100);
}

But nothing happens. If I open a serial terminal with a baudrate of 115200, nothing is printed.

[Jared]

If you go to device manger, do you see the device listed under Ports like this:

[Serafino Convertini]

I see this

COM6 and COM7 is depending on IMCU while COM13 is provided by nRF configured USB-CDC example

[Marte Myrvold]

Hi,

Are you able to get logs from COM13?

Best regards,
Marte

[Serafino Convertini]

Hi Marte,

I cannot see anything from COM13. This is the problem

[Marte Myrvold]

Hi,

When testing the CDC ACM USB sample, I saw that the log is printed on the UART port, but only if the USB is connected. I suspect this is not what you want to achieve, so I made a sample that only uses nRF USB, which I have attached here. It is the Hello World sample from Zephyr, and I only added support for CDC ACM USB, so it is very simple and should be straightforward to incorporate into other projects.

This is what the prj.conf looks like:

CONFIG_USB_DEVICE_STACK=y
CONFIG_USB_DEVICE_REMOTE_WAKEUP=n
CONFIG_USB_DEVICE_PRODUCT="My USB device"
CONFIG_USB_CDC_ACM=y
CONFIG_UART_LINE_CTRL=y
CONFIG_USB_DEVICE_PID=0x0001
CONFIG_USB_CDC_ACM_LOG_LEVEL_OFF=y

CONFIG_LOG=y

And the devicetree overlay:

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

&zephyr_udc0 {
	cdc_acm_uart0: cdc_acm_uart0 {
		compatible = "zephyr,cdc-acm-uart";
	};
};

In main,c you need to include the usb_device.h file and enable USB with usb_enable():

#include <zephyr/kernel.h>
#include <zephyr/usb/usb_device.h>
#include <zephyr/logging/log.h>

LOG_MODULE_REGISTER(app);

int main(void)
{
	usb_enable(NULL);
	printf("Hello World! %s\n", CONFIG_BOARD);
	while(true){
		LOG_INF("Hello World\n");
		/* Wait 100ms for the host to do all settings */
		k_msleep(100);
	}
	return 0;
}

hello_world_usb.zip

Please let me know if this makes it so you can get logs from the USB/COM13 or not

Best regards,
Marte