Test UART0 (TX and RX shorted) loopback failed.
The oscilloscope measurement shows the UART0 voltage is constantly “0V”.
Test UART1 (TX and RX shorted) loopback is normal.
The oscilloscope measurement shows the UART1 voltage is constantly “1.8V”.
No modifications were made to the UART0 settings. Should adjustments be made in the DTS?
Someone else will probably have to finish answering, but I want to point out some details you might not know about. First, most Jetsons use 3.3 V because they go through a level converter. The output levels at the SoC itself is 1.8 V. Developer kits should have a jumper to the level converter, and the default would be to convert to 3.3 V. You’d have to consult the docs for where the jumper is; the jumper will have no effect if you are looking at the input side of the level converter.
Second, if flow control is enabled, then I would expect a lack of CTS/RTS also being looped back to cause traffic in only one side/direction.
For the case of 1.8 V feeding a 3.3 V input, then this should fail due to levels. For the case of correct levels, then traffic will be visible in one direction without other error.
Also, if you have a custom or third party carrier board and are working on the device tree, then typically you would see each UART listed with an alias like “serial@<some physical address>”. You’d have to customize for any differences from the default dev kit UART. If this is a dev kit, then no change is needed.
The L4T release can be found with “head -n 1 /etc/nv_tegra_release”. You can then go here to find everything you need for that specific release if this is an actual dev kit and not a custom or third party carrier board:
https://developer.nvidia.com/linux-tegra
Thank you for your response.
The issue has been identified.
OS: Linux tegra-ubuntu 5.15.148-rt-tegra
Originally, on the Jetson Orin Nano reference board, UART0 is connected to the M.2 KEY-E (WiFi/Bluetooth).
Since the reference board does not have the UART0 DTS ported, it was not functioning.
The /dev/THS2 is not actually pointing to UART0.
To make it work, we just need to:
Once these changes are made, UART0 will function properly.
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