Enabling debug UART for Jetpack6.0

This guide documents the steps to enable debug UART and route UARTC on Neousys NRU-51V+ by modifying both the hardware routing and device tree (DTS / pinmux / GPIO) configuration.

🖥️ Development Environment

Item	Version / Model
Host OS	Ubuntu 20.04
L4T	L4T 36.3
Board	Neousys NRU-51V+
BSP Package	nru50+_JP60PROD_MP_2025-02-17_1116.tar.g
USB-to-TTL Cable	OP-1010C18V-PBAM04D1 (1.8 V level) — OnePing

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1. 🪛 Hardware Routing (TX/RX Wiring)

• On the NRU-51V+ carrier board, UART2_TXD (pin 236) and UART2_RXD (pin 238) are routed through 0 Ω resistors R478 (TX) and R470 (RX).

• Solder jumper wires from these resistor pads to the desired external connector.

✅ Result: UART2_V2X_TXD and UART2_V2X_RXD are now physically accessible.

2. 🧪 USB-to-TTL Adapter Connection

Use OP-101X USB-to-TTL cable (1.8 V version) on the host PC to monitor and interact with UARTC:

Signal	Jetson Pin (after routing)	USB-TTL Pin	Notes
TX	R478 pad	RX	Cross TX→RX
RX	R470 pad	TX	Cross RX→TX
GND	System ground	GND	Common ground required

⚠️ Important:

• This cable supports 1.8 V logic levels — this matches the Jetson UARTC IO voltage, so no level shifter is required.

• Do not use 5 V or 3.3 V cables directly on 1.8 V pins.

On the host PC, verify the device after plugging in:

ls /dev/ttyUSB*

For example, it may show:

/dev/ttyUSB0

Then open with:

sudo minicom -D /dev/ttyUSB0 -b 115200

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3. 📝 Pinmux Configuration

Edit:

Linux_for_Tegra/bootloader/generic/BCT/Orin-nru50+-pinmux.dtsi

uart3_tx_pcc5 {
    nvidia,pins = "uart3_tx_pcc5";
    nvidia,function = "uartc";
    nvidia,pull = <TEGRA_PIN_PULL_DOWN>;
    nvidia,tristate = <TEGRA_PIN_PULL_NONE>;
    nvidia,enable-input = <TEGRA_PIN_DISABLE>;
    nvidia,io-high-voltage = <TEGRA_PIN_DISABLE>;
    nvidia,lpdr = <TEGRA_PIN_DISABLE>;
};

uart3_rx_pcc6 {
    nvidia,pins = "uart3_rx_pcc6";
    nvidia,function = "uartc";
    nvidia,enable-input = <TEGRA_PIN_ENABLE>;
    nvidia,pull = <TEGRA_PIN_PULL_UP>;
    nvidia,tristate = <TEGRA_PIN_ENABLE>;
    nvidia,io-high-voltage = <TEGRA_PIN_DISABLE>;
    nvidia,lpdr = <TEGRA_PIN_DISABLE>;
};

✅ Result: PCC5/PCC6 pins mapped to UARTC with correct electrical characteristics.

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4. 🧭 DTS: Enabling UARTC Node

Edit:

Linux_for_Tegra/sources/hardware/nvidia/t23x/nv-public/nru_50_pcba.dtsi

		mttcan@c310000 {
			status = "okay";
		};
// --------------- Add ------------------
		serial@c280000 {  // UART C
		 	compatible = "nvidia,tegra194-hsuart";						
		 	reg = <0x0 0xc280000 0x0 0x10000>;
		 	interrupts = <0 TEGRA234_IRQ_UARTC 0x04>;			
		 	clocks = <&bpmp TEGRA234_CLK_UARTC>;
		 	resets = <&bpmp TEGRA234_RESET_UARTC>;	
		 	clock-names = "serial";
		 	reset-names = "serial";		
		 	status = "okay";
		 };
// --------------- Add ------------------
		uarte: serial@3140000 {  //UART E
		 	compatible = "nvidia,tegra194-hsuart";						
		 	reg = <0x0 0x03140000 0x0 0x10000>;
		 	interrupts = <0 TEGRA234_IRQ_UARTE 0x04>;			
		 	clocks = <&bpmp TEGRA234_CLK_UARTE>;
		 	resets = <&bpmp TEGRA234_RESET_UARTE>;	
		 	clock-names = "serial";
		 	reset-names = "serial";		
		 	status = "okay";
		};

✅ Result: UARTC is now registered as a serial device at boot.

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5. ⚡ GPIO Configuration

Edit:

Linux_for_Tegra/bootloader/generic/BCT/Orin-nru50+-gpio-default.dtsi

gpio-output-high = <
    TEGRA234_MAIN_GPIO(X, 6)
    TEGRA234_MAIN_GPIO(P, 0)
    TEGRA234_MAIN_GPIO(Q, 3)
    TEGRA234_MAIN_GPIO(H, 0)
    TEGRA234_MAIN_GPIO(A, 0)
    /* add */
    TEGRA234_MAIN_GPIO(Q, 5)
    /* add */
>;

✅ Result: Power rail for uart3 is enabled at boot.

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6. 🧪 Verification Steps

1. Updated DTB:

   cd Linux_for_Tegra
   sudo ./build_clean.sh && sudo ./build_device_tree.sh

2. Flash NRU-51V

   sudo ./flash_nru50p_dtb+pinmux.sh

3. Boot the system and check device:

   dmesg | grep ttyTHS

   Expected output:

   0xc280000.serial: ttyTHS2 at MMIO 0xc280000 (irq = 37) is a TEGRA_HSUART

4. Connect to UART via USB-TTL adapter on Host PC:

   sudo minicom -D /dev/ttyUSB0 -b 115200

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✅ Summary Table

Step	Description	File Path / Item
1	Hardware routing	R470 / R478 pads
2	USB-to-TTL connection	OP-1010C18V-PBAM04D1 1.8 V cable
3	Pinmux configuration	Orin-nru50+-pinmux.dtsi
4	Enable UARTC node	nru_50_pcba.dtsi
5	GPIO default output enable	Orin-nru50+-gpio-default.dtsi
6	Verification	Accessible through host UART terminal