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
2024/08/07	DESK-MX6UL-L 4.2.x release

Peripheral UART

Device tree configuration

AXEL ULite SOM

Here below is 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
                        >;
                };
        };
...
...

RIALTO SBC

Here below is an example of device tree configuration used on standard DAVE's kit for the RIALTO SBC:

From the SOMimx6ul-lynx-som0022.dtsi device tree:

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

		pinctrl_uart3: uart3grp {
			fsl,pins = <
				MX6UL_PAD_UART3_TX_DATA__UART3_DCE_TX 0x1b0a1
				MX6UL_PAD_UART3_RX_DATA__UART3_DCE_RX 0x1b0a1
			>;
		};
...
...
		pinctrl_uart2: uart2grp {
			fsl,pins = <
				MX6UL_PAD_UART2_TX_DATA__UART2_DCE_TX 0x1b0a1
				MX6UL_PAD_UART2_RX_DATA__UART2_DCE_RX 0x1b0a1
			>;
		};
...
...

From the Carrier imx6ul-lynx-som0022-cb0090.dts device tree:

...
...
/* RS485 on J3 of RTIN add-on */
&uart2 {
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_uart2>;
	status = "okay";
};

/* RS232 on J67 */
&uart3 {
	status = "okay";
};

/* RS485 on J4 of RTIN add-on */
&uart5 {
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_uart5>;
	status = "okay";
};
...
...
&iomuxc {
...
...

		pinctrl_uart5: uart5grp {
			fsl,pins = <
				MX6UL_PAD_GPIO1_IO04__UART5_DCE_TX	0x1b0a1
				MX6UL_PAD_GPIO1_IO05__UART5_DCE_RX	0x1b0a1
			>;
		};
...
...
		pinctrl_uart2: uart2grp {
			fsl,pins = <
				MX6UL_PAD_UART2_TX_DATA__UART2_DCE_TX 0x1b0a1
				MX6UL_PAD_UART2_RX_DATA__UART2_DCE_RX 0x1b0a1
			>;
		};

...
...

Accessing the peripheral in AXEL ULite SOM

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

Accessing the peripheral in RIALTO SBC

Linux messages at boot time

...
...
[    1.332721] 21e8000.serial: ttymxc1 at MMIO 0x21e8000 (irq = 65, base_baud = 5000000) is a IMX
[    1.343551] 21ec000.serial: ttymxc2 at MMIO 0x21ec000 (irq = 66, base_baud = 5000000) is a IMX
[    1.354436] 21f4000.serial: ttymxc4 at MMIO 0x21f4000 (irq = 67, 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, to use UART232, using a loopback HW connection (RX short-circuited to TX on UART232) it is possible to test the send and receive data using the ttymxc2 device:

root@desk-mx6ul-rialto:~# stty -F /dev/ttymxc2 115200 -echo
root@desk-mx6ul-rialto:~# cat /dev/ttymxc2 &
[1] 313
root@desk-mx6ul-rialto:~# echo "Test loopback RS232" > /dev/ttymxc2
root@desk-mx6ul-rialto:~# Test loopback RS232

For example, to use UART485, using a loopback HW connection (RX short-circuited to TX of UART285 on J3 and J4 of RTIN add-on ) it is possible to test the send and receive data using the ttymxc1 and ttymxc4 device:

root@desk-mx6ul-rialto:~# stty -F /dev/ttymxc1 115200 -echo
root@desk-mx6ul-rialto:~# stty -F /dev/ttymxc4 115200 -echo
root@desk-mx6ul-rialto:~# cat /dev/ttymxc4 &
[2] 316
root@desk-mx6ul-rialto:~# cat /dev/ttymxc1 &
[3] 317
root@desk-mx6ul-rialto:~# echo "Send message from ttymxc1 to ttymxc4!" > /dev/ttymxc1
Send message from ttymxc1 to ttymxc4!
root@desk-mx6ul-rialto:~# echo "Send message from ttymxc4 to ttymxc1!" > /dev/ttymxc4
Send message from ttymxc4 to ttymxc1!

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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