Connectivity bridge on NRF52840 based custom board

[Andrei H.]

Hi,

 Tried to use Connectivity bridge app on a custom board based on NRF52840 and it seems that the UART-USB interface works initially, but after a while it gets stuck at communication level. The goal is to use it in the same way USBD_CDC_ACM sample. Opening a console to that stuck PORT makes it work again for a while. The CDC_ACM / UART control lines are enabled and they should work normally, since, on the same board, the USBD_CDC_ACM sample does not have this problem.

 Configuration:

# Features
CONFIG_BRIDGE_MSC_ENABLE=n
CONFIG_BRIDGE_BLE_ENABLE=n

Overlay file:

&uart1 {
	compatible = "nordic,nrf-uarte";
	status = "okay";
};

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

	cdc_acm_uart1: cdc_acm_uart1 {
		compatible = "zephyr,cdc-acm-uart";
	};

	rtt0: rtt_chan0 {
		compatible = "segger,rtt-uart";
		status = "okay";
	};
};

/ {
	chosen {
		zephyr,console = &rtt0;
		zephyr,shell-uart = &rtt0;
		zephyr,uart-mcumgr = &rtt0;
	};
};

I would like to know what is the cause of this behaviour.

Regards.

[Andrei H.]

Hi,

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

Regards.

[Kenneth]

Hi,

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

Kenneth

[Andrei H.]

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.

[Kenneth]

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

[Andrei H.]

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.

[Kenneth]

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

[Andrei H.]

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.

[Kenneth]

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

Kenneth

[Andrei H.]

Hi Kenneth,

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

logic_analyzer_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:

USBD_CDC_ACM_sample_variant.sal

* this variant works fine.

Regards.