Any specific configuration for enabling UART between Zephyr boards and Arduino boards?

[alexpaschoaletto]

I'm feeling pretty dumb at the moment for making such a question, but I've ran completely out of ideas and am starting to become desperate.

Here's the thing: I have two boards in a circuit. One is a Raspberry Pi Pico, and the other is an ESP8266. The raspberry is programmed with Zephyr, the ESP8266 with the Arduino "API" thing (for now I can't really change that). And more importantly, both have UART enabled and are connected with one another. Yet... I can't seem to make they communicate. As in: No messages sent by the Pico seem to be received by the ESP, and vice-versa. Some observations:

• if I plug a CH340 USB-to-serial driver on each end separately and simulate the other device, both respond exactly as they should.
• I have double-checked the connections, and they are correct.
• There is guaranteedly no faulty wires in the line. All wires are conducting electricity as intended.
• The ESP is configured with Serial.begin(115200, SERIAL_8N1) to ensure the baud rate, parity, stop bits and data bits.
• The Raspberry Pi Pico uart0 generated dts snippet is configured as below.

&pinctrl {
    test_uart: test_uart {
		group1 {
			pinmux = <UART0_TX_P16>;
		};
		group2 {
			pinmux = <UART0_RX_P17>;
			input-enable;
		};
	};
};

uart0: pico_serial: uart@40034000 {
	compatible = "raspberrypi,pico-uart",
			           "arm,pl011";             
	reg = < 0x40034000 0x1000 >;          
	clocks = < &clocks 0x6 >;             
	resets = < &reset 0x16 >;             
	interrupts = < 0x14 0x3 >;            
	interrupt-names = "uart0";           
	status = "okay";                      
	current-speed = < 115200 >;         
	pinctrl-0 = < &test_uart >;        
	pinctrl-names = "default";            
	parity = "none";                      
	stop-bits = "1";                      
	data-bits = < 0x8 >;               
};

So by any chance does anyone have any idea of what might be possibly happening? I'm so sad right now 🥲
Many many thanks in advance.

[Gerriko]

I have double-checked the connections, and they are correct.

Hmmm. Show us proof, otherwise you could be making an "ass" out of "u" and "me" (i.e. we're having to assume).
E.g. A dumb question, but have you connected GND between the two boards.
Otherwise, have you configured prj.conf correctly?