DESK-MX6UL-L/Peripherals/UART

History
Issue Date	Notes
2021/07/20	First DESK-MX6UL-L release
2022/03/16	DESK-MX6UL-L 3.0.0 release
2023/05/04	DESK-MX6UL-L 4.0.0 release

Peripheral UART

Device tree configuration

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

From the Carrier imx6ul-axelulite-cb003a.dts device tree:

&uart3 {
        pinctrl-names = "default";
        pinctrl-0 = <&pinctrl_uart3>;
        status = "okay";
};
...
...
&iomuxc {
        pinctrl-names = "default";
        pinctrl-0 = <&pinctrl_hog_gpios>;

        imx6ul-axelulite {
...
...
        uart {
                pinctrl_uart3: uart3grp {
                        fsl,pins = <
                                MX6UL_PAD_UART3_RX_DATA__UART3_DCE_RX   0x1b0b1
                                MX6UL_PAD_UART3_TX_DATA__UART3_DCE_TX   0x1b0b1
                        >;
                };
        };
...
...

Accessing the peripheral

Linux messages at boot time

...
...
[    0.569198] 2020000.serial: ttymxc0 at MMIO 0x2020000 (irq = 30, base_baud = 5000000) is a IMX
[    1.344706] 21ec000.serial: ttymxc2 at MMIO 0x21ec000 (irq = 65, base_baud = 5000000) is a IMX
...
...

Usage with stty

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

UART1 <-> ttymxc0
UART2 <-> ttymxc1
UART3 <-> ttymxc2
UART4 <-> ttymxc3
UART5 <-> ttymxc4
UART6 <-> ttymxc5
UART7 <-> ttymxc6
UART8 <-> ttymxc7
...

For example, using a loopback HW connection (RX short circuited to TX on UART232 port) it is possible to test the send and receive data using the ttymxc2 device:

root@desk-mx6ul-axelulite:~# stty -F /dev/ttymxc2 115200 -echo
root@desk-mx6ul-axelulite:~# cat /dev/ttymxc2 &
[1] 267
root@desk-mx6ul-axelulite:~# echo "Test loopback" > /dev/ttymxc2
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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