Connectivity bridge on NRF52840 based custom board

RE: Connectivity bridge on NRF52840 based custom board

Andrei H. — Thu, 05 Jun 2025 09:02:27 GMT

Hi Kenneth,

1. Attaching trace with the communication, with `uart_passthrough` example:

devzone.nordicsemi.com/.../logic_5F00_analyzer_5F00_UART0.sal

* if I'm trying to send a char to the device it hangs.

2. For comparison, this is the logic analyzer trace with the `usbd_cdc_acm` sample:

devzone.nordicsemi.com/.../USBD_5F00_CDC_5F00_ACM_5F00_sample_5F00_variant.sal

* this variant works fine.

Regards.

RE: Connectivity bridge on NRF52840 based custom board

Kenneth — Wed, 04 Jun 2025 06:49:56 GMT

I suggest to connect a logic analyzer on the 4 pins in questions, so we can see what is actually happening.

Kenneth

RE: Connectivity bridge on NRF52840 based custom board

Andrei H. — Tue, 03 Jun 2025 15:47:25 GMT

Hi Kenneth,

I've modified my custom_board.dts to have those but the result is the same. e.g.:

&pinctrl {
	uart0_default: uart0_default {
		group1 {
			psels = <NRF_PSEL(UART_RX,  0, 25)>,
					<NRF_PSEL(UART_CTS, 0, 15)>;
			bias-pull-up;
		};
		group2 {
			psels = <NRF_PSEL(UART_TX,  0, 11)>,
					<NRF_PSEL(UART_RTS, 0, 27)>;

		};
	};

	uart0_sleep: uart0_sleep {
		group1 {
			psels = <NRF_PSEL(UART_TX,  0, 11)>,
					<NRF_PSEL(UART_RX,  0, 25)>,
					<NRF_PSEL(UART_CTS, 0, 15)>,
					<NRF_PSEL(UART_RTS, 0, 27)>;
			low-power-enable;
		};
	};
...

*** Booting nRF Connect SDK v3.0.0-3bfc46578e42 ***
*** Using Zephyr OS v4.0.99-3e0ce7636fa6 ***
<<o2c: UART error: 0xc>>

Update, I've run this with the delay, this is the result:

*** Delaying boot by 4000ms... ***
*** Booting nRF Connect SDK v3.0.0-3bfc46578e42 ***
*** Using Zephyr OS v4.0.99-3e0ce7636fa6 ***
<<o2c: UART error: 0xc>>

Best regards.

RE: Connectivity bridge on NRF52840 based custom board

Kenneth — Tue, 03 Jun 2025 15:20:35 GMT

Hi,

Floating RXD pin can cause such issue yes. If you don't have the possibility to add an external pull-up, you can use the internal one, something like this (look for 'bias-pull-up;' for the RXD pin):

&pinctrl {
	uart1_default: uart1_default {
		group1 {
			psels = <NRF_PSEL(UART_RX, 1, 1)>;
			bias-pull-up;
		};
		group2 {
			psels = <NRF_PSEL(UART_TX, 1, 2)>;
		};
	};

	uart1_sleep: uart1_sleep {
		group1 {
			psels = <NRF_PSEL(UART_RX, 1, 1)>,
				<NRF_PSEL(UART_TX, 1, 2)>;
			low-power-enable;
		};
	};
};

Kenneth

RE: Connectivity bridge on NRF52840 based custom board

Andrei H. — Tue, 03 Jun 2025 13:37:25 GMT

Hi,

I'm using a custom board and the RXD is connected between the MCU and the peripheral there is no pull-up resistor. The passthrough is suppose to be between the USB-port `cdc_acm_uart0` and UART0 peripheral. For context, the `USBD_CDC_ACM sample` works fine, only the `UART Passthrough` sample (and the `connectivity_bridge` sample) have this problem.

Could be that until USB is initialized some floating pins can cause this issue? so maybe `CONFIG_BOOT_DELAY` could ensure that the USB stack is properly initialized? (although I think I tried this and it didnt help).

Regards.

RE: Connectivity bridge on NRF52840 based custom board

Kenneth — Tue, 03 Jun 2025 11:45:58 GMT

Looks like you experience both an break and framing error, ref:
https://docs.nordicsemi.com/bundle/ps_nrf52840/page/uarte.html#ariaid-title31

Can you add a pull-up resistor on the UART RXD line? Or ensure otherwise it's always high when there is no serial data.

Kenneth

RE: Connectivity bridge on NRF52840 based custom board

Andrei H. — Mon, 02 Jun 2025 18:13:25 GMT

Hi Kenneth,

I've tried that example and it doesnt seem to work, I get this:

*** Booting nRF Connect SDK v3.0.0-3bfc46578e42 ***
*** Using Zephyr OS v4.0.99-3e0ce7636fa6 ***
<<o2c: UART error: 0xc>>

I've added support for CDC_ACM from the original description in this new example:

custom_board.conf:

CONFIG_CONSOLE=y

CONFIG_UART_CONSOLE=y
CONFIG_UART_LINE_CTRL=y

CONFIG_USB_DEVICE_STACK=y
CONFIG_USB_DEVICE_PRODUCT="Zephyr USB console sample"
CONFIG_USB_DEVICE_PID=0x0004
CONFIG_USB_DEVICE_INITIALIZE_AT_BOOT=y

custom_board.overlay:

/ {
	chosen {
		zephyr,console = &cdc_acm_uart0;
        uart,passthrough = &uart0;
	};
};

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

Best regards.

RE: Connectivity bridge on NRF52840 based custom board

Kenneth — Mon, 02 Jun 2025 15:53:29 GMT

Hi,

Can you try this one: https://github.com/martelmy/NCS_examples/tree/main/peripherals/uart_passthrough

Kenneth

RE: Connectivity bridge on NRF52840 based custom board

Andrei H. — Fri, 30 May 2025 06:07:10 GMT

Hi,

[Update]: UART Passthrough behave the same, hangs at some point in communication.

Regards.