DESK-MX6UL-L/Peripherals/UART

History
Version	Issue Date	Notes
1.0.0	Apr 2021	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 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

...
...
[    0.437613] 2020000.serial: ttymxc0 at MMIO 0x2020000 (irq = 21, base_baud = 5000000) is a IMX
[    1.167221] console [ttymxc0] enabled
[    1.172839] 21ec000.serial: ttymxc2 at MMIO 0x21ec000 (irq = 58, 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 exmaple, using a loopback HW connection (RX shortcircuited to TX on UART232 port) it is possibile 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] 266
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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