UART¶

VAR-SOM-MX8X UART Overview¶

On VAR-SOM-MX8X up to 4 UARTs can be used.
All 4 UARTs are enabled by default.
UART3 is used for the debug console, UART0, UART1 and UART2 are connected to J18 header on Symphony-Board.
UART0 is connected to Bluetooth module on SOM, it can be used on J18 only when BT is disabled.
Only UART0 and UART1 have RTS and CTS lines. Inspect the carrier board datasheet or schematics for the exact pinout.

UART naming under Linux¶

The Linux devices corresponding to UART0 - UART4 are /dev/ttyLP0 - /dev/ttyLP4 respectively.

Testing UART1¶

Short J18.3 and J18.5 pins and run the following commands:

stty -F /dev/ttyLP1 -echo -onlcr 115200
cat /dev/ttyLP1 &
echo hello > /dev/ttyLP1

For each invocation of the echo command the "hello" string should appear on the terminal.

Testing UART2¶

Short J18.7 and J18.9 pins and run the following commands:

stty -F /dev/ttyLP2 -echo -onlcr 115200
cat /dev/ttyLP2 &
echo hello > /dev/ttyLP2

For each invocation of the echo command the "hello" string should appear on the terminal.

Disabling UART1¶

To disable UART1 edit arch/arm64/boot/dts/freescale/fsl-imx8qxp-var-som-common.dtsi in the kernel source directory and modify

&lpuart1 {
        ...
        status = "okay";
};

to

&lpuart1 {
        ...
        status = "disabled";
};

Other UARTs can be disabled in a similar manner.