MX8 UART

VAR-SOM-MX8X UART

VAR-SOM-MX8X UART Overview

All 4 UARTs on VAR-SOM-MX8X are enabled by default.
UART1 is connected to Bluetooth module, UART2 and UART3 are connected to J18 header on VAR-SOM-MX8X carrier board, UART4 is used as a debug console.
On VAR-SOM-MX8X SoMs without WIFI/BT module UART1 is also connected to J18 header.
Inspect the carrier board datasheet or schematics for the exact pinout.
Only UART1 has RTS and CTS lines.

UART naming under Linux

The Linux devices corresponding to UART1 - UART4 are /dev/ttyLP0 - /dev/ttyLP3 respectively.

Testing UART2

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 time you run this echo command the "hello" string should appear on the terminal.

Testing UART3

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 echo command the "hello" string should appear on the terminal.

Disabling UART2

To disable UART2 edit arch/arm64/boot/dts/freescale/fsl-imx8qxp-var-som-common.dtsi under kernel source directory and modify

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

to

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

Other UARTs can be disabled in the similar manner.