DESK-MX6-L/Pheripherals/UART

History
Version	Issue Date	Notes
1.0.0	Oct 2020	First DESK release
2.0.0	Feb 2022	DESK 3.0.0 release

Peripheral UART

Device tree configuration

Here below an example of device tree configuration used on standard DAVE's kit for the AXELLite SOM:

From imx6qdl-sbcx-revb-common.dtsi:

&uart2 {
	fsl,uart-has-rtscts;
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_dwm_uart2_1>;
	status = "okay";
};

From imx6qdl-axelcommon.dtsi:

    uart2 {
        pinctrl_dwm_uart2_1: dwm_uart2_grp-1 {
            fsl,pins = <
                MX6QDL_PAD_SD3_DAT4__UART2_RX_DATA 0x1b0b1
                MX6QDL_PAD_SD3_DAT5__UART2_TX_DATA 0x1b0b1
                MX6QDL_PAD_SD3_CMD__UART2_CTS_B 0x1b0b1
                MX6QDL_PAD_SD3_CLK__UART2_RTS_B 0x1b0b1
            >;
        };

Accessing the peripheral

Linux messages at boot time

...
...
[    1.010016] 21e8000.serial: ttymxc1 at MMIO 0x21e8000 (irq = 78, base_baud = 5000000) is a IMX
[    1.011009] 21ec000.serial: ttymxc2 at MMIO 0x21ec000 (irq = 79, base_baud = 5000000) is a IMX
[    2.198543] 21f0000.serial: ttymxc3 at MMIO 0x21f0000 (irq = 80, base_baud = 5000000) is a IMX
[    2.208297] 21f4000.serial: ttymxc4 at MMIO 0x21f4000 (irq = 81, base_baud = 5000000) is a IMX
...
...
root@imx6qxelk:~#

Configuring the RS232/RS485 mode

When the UART5 (aka /dev/ttymxc4 device in Linux) is properly configured using the hardware jumpers (see Interfaces and Connectors - UART5 EVK page), the MultiProtocol transceiver pins has to be initialized for setting the related user selectable modes: the RS232 or RS485 mode can be selected with the gpio-leds class and the led rs232_on.

From imx6q-sbcx-cb0012.dts or imx6dl-sbcx-cb0012.dts:

    leds {
	compatible = "gpio-leds";
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_rs232_485_422_1>;

	rs232_485_422 {
		gpios = <&gpio7 13 GPIO_ACTIVE_HIGH>;
		linux,default-trigger = "default-on";
	};

	rs232_on {
		gpios = <&gpio5 29 GPIO_ACTIVE_LOW>;
		linux,default-trigger = "default-on";
	};
    };

RS232 mode

This is the default protocol mode; this can be also activated (when different) using the following command:

root@desk-mx6:~# echo 0 > /sys/class/leds/rs232_on/brightness

RS485 mode

This mode can be activated using the following command:

root@desk-mx6:~# echo 255 > /sys/class/leds/rs232_on/brightness

Usage with stty

N.B. UART mapping respect to ttymxcX is the following one:

UART1 <-> ttymxc0
UART2 <-> ttymxc1
UART3 <-> ttymxc2
UART4 <-> ttymxc3
...

root@desk-mx6:~# stty -F /dev/ttymxc3 115200 -echo
root@desk-mx6:~# cat /dev/ttymxc3 &
[2] 555
root@desk-mx6:~# echo "Test loopback" > /dev/ttymxc3
root@desk-mx6:~# Test loopback

Additional information

Serial ports can be used through the standard serial programming API.

For detailed information, please refer to the Serial Programming HOWTO at Serial-Programming-HOWTO

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