4.4. UART Configuration

Attention

By default UART0 is used as a login terminal. Do not change this, unless there is a compelling reason to do so.

We have made the decision to use UART5 for the telemetry communication with the FCU. UART4 is connected to the debug port of the FCU.

4.4.1. Enable UARTs

Edit the config file

sudo vim /boot/firmware/config.txt

and append the dtoverlay= lines for the required UARTs.

dtoverlay=uart2
dtoverlay=uart4
dtoverlay=uart5

4.4.2. UART-KERNELS-Pin Mapping

The UART functions in the following table depend on whether Raspberry Pi is used in a UUV or for the gantry controlling computer.

UART	KERNELS	Tx/Rx GPIOs
0		`GPIO14/GPIO15`
1
2	`fe201400.serial`	`GPIO0/GPIO1`
3	`fe201600.serial`	`GPIO4/GPIO5`
4	`fe201800.serial`	`GPIO8/GPIO9`
5	`fe201a00.serial`	`GPIO12/GPIO13`

4.4.3. Pinout

4.4.4. UART Rule

Create the file /etc/udev/rules.d/50-serial.rules with the following content:

KERNEL=="ttyAMA[0-9]*", GROUP="dialout", ENV{SERIAL_MARKER}="fcu_serial"

# uart4
ENV{SERIAL_MARKER}=="fcu_serial",  SUBSYSTEM=="tty", KERNELS=="fe201800.serial", SYMLINK+="fcu_debug"
# uart5
ENV{SERIAL_MARKER}=="fcu_serial",  SUBSYSTEM=="tty", KERNELS=="fe201a00.serial", SYMLINK+="fcu_data"

KERNEL=="ttyAMA[0-9]*", GROUP="dialout", ENV{SERIAL_MARKER}="serial_marker"

# uart2
ENV{SERIAL_MARKER}=="serial_marker",  SUBSYSTEM=="tty", KERNELS=="fe201400.serial", SYMLINK+="teensy_data"
# uart4
ENV{SERIAL_MARKER}=="serial_marker",  SUBSYSTEM=="tty", KERNELS=="fe201800.serial", SYMLINK+="fcu_debug"
# uart5
ENV{SERIAL_MARKER}=="serial_marker",  SUBSYSTEM=="tty", KERNELS=="fe201a00.serial", SYMLINK+="fcu_data"

KERNEL=="ttyAMA[0-9]*", GROUP="dialout", ENV{SERIAL_MARKER}="motor_serial"

# uart2
ENV{SERIAL_MARKER}=="motor_serial",  SUBSYSTEM=="tty", KERNELS=="fe201400.serial", SYMLINK+="motor_x"
# uart4
ENV{SERIAL_MARKER}=="motor_serial",  SUBSYSTEM=="tty", KERNELS=="fe201800.serial", SYMLINK+="motor_y"
# uart5
ENV{SERIAL_MARKER}=="motor_serial",  SUBSYSTEM=="tty", KERNELS=="fe201a00.serial", SYMLINK+="motor_z"

You can apply these changes by

$ sudo udevadm control --reload-rules && sudo udevadm trigger

To check, that the rule is applied correctly, you can execute

ls /dev/fcu* -l

ls /dev/motor* -l

The output should show symbolic links for the serial devices:

lrwxrwxrwx 1 root root 7 Dec 11 14:57 /dev/fcu_debug -> ttyAMA1
lrwxrwxrwx 1 root root 7 Dec 11 14:57 /dev/fcu_tele -> ttyAMA2

lrwxrwxrwx 1 root root 7 Aug  7 01:00 /dev/motor_x -> ttyAMA2
lrwxrwxrwx 1 root root 7 Aug  7 01:00 /dev/motor_y -> ttyAMA3
lrwxrwxrwx 1 root root 7 Aug  7 01:00 /dev/motor_z -> ttyAMA4

Note

The ttyAMA numbers might differ, depending on the UARTs you have activated.

4.4.5. Identify KERNELS

To identify the KERNELS paramter of a certain ttyAMA device, execute the following command.

$ udevadm info --name=/dev/ttyAMA1 --attribute-walk

looking at device '/devices/platform/soc/fe201800.serial/tty/ttyAMA1':
KERNEL=="ttyAMA1"
SUBSYSTEM=="tty"
DRIVER==""

looking at parent device '/devices/ platform/soc/fe201800.serial':
KERNELS=="fe201800.serial"
SUBSYSTEMS=="amba"
DRIVERS=="uart-pl011"
ATTRS{driver_override}=="(null)"
ATTRS{id}=="00241011"
ATTRS{irq0}=="14"

looking at parent device '/devices/ platform/soc':
KERNELS=="soc"
SUBSYSTEMS=="platform"
DRIVERS==""
ATTRS{driver_override}=="(null)"

looking at parent device '/devices/ platform':
KERNELS=="platform"
SUBSYSTEMS==""
DRIVERS==""

Attention

The ttyAMAx number is not specific for the UART device and depends on how many UARTs are activated.