Serial Port Mapping
This topic shows how to determine the mapping between serial ports (UART), device (e.g. "ttyS0") and specific functions enabled by PX4 (e.g. TELEM1, TELEM2, GPS1, RC SBUS, Debug console).
The instructions are used to generate serial port mapping tables in flight controller documentation. For example: Pixhawk 4 > Serial Port Mapping.
NuttX on STMxxyyy
This section shows how to get the mappings for NuttX builds on STMxxyyy architectures by inspecting the board configuration files. The instructions use FMUv5, but can similarly be extended for other FMU versions/NuttX boards.
default.px4board
The default.px4board lists a number of serial port mappings (search for the text "SERIAL_PORTS").
From /boards/px4/fmu-v5/default.px4board:
Alternatively you can launch boardconfig using make px4_fmu-v5 boardconfig
and access the serial port menu
nsh/defconfig
The nsh/defconfig allows you to determine which ports are defined, whether they are UART or USARTs, and the mapping between USART/UART and device. You can also determine which port is used for the serial/debug console.
Open the board's defconfig file, for example: /boards/px4/fmu-v5/nuttx-config/nsh/defconfig
Search for the text "ART" until you find a section like with entries formatted like CONFIG_STM32xx_USARTn=y
(where xx
is a processor type and n
is a port number). For example:
The entries tell you which ports are defined, and whether they are UART or USART.
Copy the section above and reorder numerically by "n". Increment the device number ttySn alongside (zero based) to get the device-to-serial-port mapping.
To get the DEBUG console mapping we search the defconfig file for SERIAL_CONSOLE
. Below we see that the console is on UART7:
board_config.h
For flight controllers that have an IO board, determine the PX4IO connection from board_config.h by searching for PX4IO_SERIAL_DEVICE
.
For example, /boards/px4/fmu-v5/src/board_config.h:
So the PX4IO is on ttyS6
(we can also see that this maps to UART8, which we already knew from the preceding section).
Putting it all together
The final mapping is:
In the flight controller docs the resulting table is:
UART | Device | Port |
---|---|---|
UART1 | /dev/ttyS0 | GPS |
USART2 | /dev/ttyS1 | TELEM1 (flow control) |
USART3 | /dev/ttyS2 | TELEM2 (flow control) |
UART4 | /dev/ttyS3 | TELEM4 |
USART6 | /dev/ttyS4 | RC SBUS |
UART7 | /dev/ttyS5 | Debug Console |
UART8 | /dev/ttyS6 | PX4IO |
Other Architectures
Contributions welcome!
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