Why I can get "Message from SPE R5 UART" in UARTC?

The uart.md of SPE sample document mentions that
5.2 Use a wire to connect UARTC TX and Rx (in Jetson TX2 carrier board, they
are pin 5 and 4 in J17), then the following message will output from
SPE firmware debug UART port, i.e. UARTG:
Message from SPE R5 UART

But I get “Message from SPE R5 UART” message which should be printed out through J10(UARTG) when I use a usb connect to J17(UARTC). And I can’t get “GPIO input irq triggered” message when I follow the steps of gpio.md in the same UARTC.

Beware that J17’s default UART function is the serial console. Serial console will also have certain error messages echoed to it (a lot echoes to this UART during boot, and then after boot some errors or other conditions may echo to this UART…not because it is a UART, but instead because it is an admin console).

I don’t know about the specifics of the SPE messages, e.g., I don’t know what might cause this to log something at an error level.

Hello, garretzou:
Would you please take a look at https://devtalk.nvidia.com/default/topic/1062575/freertos-spe-fw-help-for-pin-control-
Some detailed information about UART/GPIO app in SPE firmware are pasted in that thread.

Let me know if you still have any problem.