MX8 UART

UART

UART Overview

On VAR-SOM-MX8 up to 5 UARTS can be used.
By default, UART0, UART1, UART2 and UART4 are enabled, UART3 is disabled as it shares pins with the second Ethernet controller. UART5 is not defined.
UART0 is used for debug console, UART1, UART2 and UART4 are connected to J18 header on Symphony-Board. UART3 is connected to J30 header on Symphony-Board (not assembled by default).
UART1 is connected to Bluetooth module on SOM, it can be used on J18 only when BT is disabled.
Only UART0, UART1 and UART3 have RTS and CTS lines.
Inspect the carrier board datasheet or schematics for the exact pinout.

On SPEAR-MX8 up to 5 UARTS can be used.
By default, UART0, UART1 and UART2 are enabled, and UART3 and UART4 are not defined (UART3 shares pins with the second Ethernet controller).
UART0 is used for debug console, UART0 and UART2 are connected to J26 header on SPEAR-CustomBoard. UART3 and UART4 are connected to J20 header on the SPEAR-CustomBoard.
UART1 is connected to the Bluetooth module on the SOM. it can be used only when BT is disabled (not exported on SPEAR-CustomBoard).
Only UART0, UART1 and UART3 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 UART2 on VAR-SOM-MX8

Short J18.3 and J18.5 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.

Testing UART4 on VAR-SOM-MX8

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

stty -F /dev/ttyLP4 -echo -onlcr 115200
cat /dev/ttyLP4 &
echo hello > /dev/ttyLP4

Testing UART2 on SPEAR-MX8

Short J26.17 and J26.19 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 on VAR-SOM-MX8 edit arch/arm64/boot/dts/freescale/fsl-imx8qxp-var-som-common.dtsi under kernel source directory and modify

&lpuart2 {
        ...
        status = "okay";
};

to

&lpuart2 {
        ...
        status = "disabled";
};

On SPEAR-MX8 modify arch/arm64/boot/dts/freescale/fsl-imx8qxp-var-spear-common.dtsi in the same manner.