MX8 UART

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VAR-SOM-MX8X UART

1 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 as for 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, UART1 have RTS and CTS lines. Inspect the carrier board datasheet or schematics for the exact pinout.

2 UART naming under Linux

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

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

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

5 Disabling UART1

To disable UART1 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.