How do you use the Debug UART feature as a regular UART on the Xavier NX board?

Robotics & Edge Computing Jetson & Embedded Systems Jetson Xavier NX
1

We designed a custom carrier board using the Xavier NX module.

We have to use all UART ports on the Xavier NX board.

Therefore, we need a way to disable the debug function in UART2 and use it as a normal UART.
(pin 236 , 238)

What are some ways to use that function?

3

hello bluesky4663 ,

please check this topic, NX change console to other uart - #11 by JerryChang
thanks

4

Hi, Jerry

I modified the code as follows.

$OUT/Linux_for_Tegra/bootloader/t186ref/BCT/tegra194-mb1-bct-misc-l4t.cfg

-enable_combined_uart = 1;
+enable_combined_uart = 0;
-spe_uart_instance = 0x2;
+spe_uart_instance = 0xff;

$OUT/Linux_for_Tegra/bootloader/t186ref/BCT/tegra194-mb1-soft-fuses-l4t.cfg

-Verbosity = 4; # 0: Disabled: 1: Critical, 2: Error, 3: Warn, 4: Info, 5: Debug
+Verbosity = 0; # 0: Disabled: 1: Critical, 2: Error, 3: Warn, 4: Info, 5: Debug

However, if you change it and flash the board, the board stops during kernel booting.

And I restored only 'tegra194-mb1-bct-misc-l4t.cfg ’ to its original state.

enable_combined_uart = 1;
spe_uart_instance = 0x2;

Then, the OS booting was completed normally.

Is there a part where I missed something?

5

hello bluesky4663,

since you’re going to disable the combined UART (i.e. TCU), please also remove ttyTCU0 in the device tree to configure console.
for example,

--- a/common/tegra194-p3668-common.dtsi
+++ b/common/tegra194-p3668-common.dtsi
@@ -33,7 +33,7 @@
        chosen {
-               bootargs ="console=ttyTCU0,115200";
+               bootargs ="console=none console=tty0";
6

Hi. Jerry

As you said, we revised the code.

$OUT/Linux_for_Tegra/bootloader/t186ref/BCT/tegra194-mb1-bct-misc-l4t.cfg

-enable_combined_uart = 1;
+enable_combined_uart = 0;
-spe_uart_instance = 0x2;
+spe_uart_instance = 0xff;

$OUT/Linux_for_Tegra/bootloader/t186ref/BCT/tegra194-mb1-soft-fuses-l4t.cfg

-Verbosity = 4; # 0: Disabled: 1: Critical, 2: Error, 3: Warn, 4: Info, 5: Debug
+Verbosity = 0; # 0: Disabled: 1: Critical, 2: Error, 3: Warn, 4: Info, 5: Debug

Linux_for_Tegra/source/public/hardware/nvidia/platform/t19x/jakku/kernel-dts/common/tegra194-p3668-common.dtsi

chosen {
- bootargs =“console=ttyTCU0,115200”;
+ bootargs =“console=none console=tty0”;
board-has-eeprom;
nvidia,tegra-joint_xpu_rail;
};

Likewise, if you change it and flash the board, the board stops during kernel booting.

And I restored only 'tegra194-mb1-bct-misc-l4t.cfg ’ to its original state.

Then, the OS booting was completed normally.

What’s the problem?

7

hello bluesky4663,

what did you mean the board stops during kernel booting. there’s nothing output to the console since you’ve disable the logs.
what if you kept enable_combined_uart = 1; and spe_uart_instance = 0x2;, and simply remove ttyTCU0 in the device tree?

8

Hi. Jerry.

That’s mean the screen is not displayed.

We measured Xavier NX pin 236 with an oscilloscope.
(We used a level shifter and measured Non-jetson-nx side.)

Pin 236 confirmed that the signal did not move when booting.

I left it for a long time, but the booting didn’t proceed.

if i kept enable_combined_uart = 1; and spe_uart_instance = 0x2;, ttyTCU0 exists in the device tree.