DESK-MX6UL-L/Peripherals/UART

History
Version	Issue Date	Notes
1.0.0	Apr 2021	First DESK release
3.0.0	Feb 2022	3.0.0 DESK release

Contents

Peripheral UARTEdit

Device tree configurationEdit

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

From the Carrier imx6ul-lynx-som0013-cb002f.dts device tree:

[ 1.163365] 2020000.serial: ttymxc0 at MMIO 0x2020000 (irq = 30, base_baud = 5000000) is a IMX

[ 1.923126] 21ec000.serial: ttymxc2 at MMIO 0x21ec000 (irq = 65, base_baud = 5000000) is a IMX

and from imx6ul-lynx-som0013.dtsi

		pinctrl_uart1: uart1grp {
			fsl,pins = <
				MX6UL_PAD_UART1_TX_DATA__UART1_DCE_TX 0x1b0b1
				MX6UL_PAD_UART1_RX_DATA__UART1_DCE_RX 0x1b0b1
			>;
		};

		pinctrl_uart2: uart2grp {
			fsl,pins = <
				MX6UL_PAD_UART2_TX_DATA__UART2_DCE_TX 0x1b0b1
				MX6UL_PAD_UART2_RX_DATA__UART2_DCE_RX 0x1b0b1
			>;
		};

		pinctrl_uart2_flow: uart2grp-flow {
			fsl,pins = <
				MX6UL_PAD_UART2_TX_DATA__UART2_DCE_TX 0x1b0b1
				MX6UL_PAD_UART2_RX_DATA__UART2_DCE_RX 0x1b0b1
				MX6UL_PAD_UART2_CTS_B__UART2_DCE_CTS  0x1b0b1
				MX6UL_PAD_UART2_RTS_B__UART2_DCE_RTS  0x1b0b1
			>;
		};

		pinctrl_uart3: uart3grp {
			fsl,pins = <
				MX6UL_PAD_UART3_TX_DATA__UART3_DCE_TX 0x1b0b1
				MX6UL_PAD_UART3_RX_DATA__UART3_DCE_RX 0x1b0b1
			>;
		};

		pinctrl_uart3_flow: uart3grp-flow {
			fsl,pins = <
				MX6UL_PAD_UART3_TX_DATA__UART3_DCE_TX 0x1b0b1
				MX6UL_PAD_UART3_RX_DATA__UART3_DCE_RX 0x1b0b1
				MX6UL_PAD_UART3_CTS_B__UART3_DCE_CTS  0x1b0b1
				MX6UL_PAD_UART3_RTS_B__UART3_DCE_RTS  0x1b0b1
			>;
		};


		pinctrl_uart3_config: uart3grp-config {
			fsl,pins = <
				MX6UL_PAD_CSI_PIXCLK__GPIO4_IO18	0x80000000 /* MPUART1_ON */
				MX6UL_PAD_SNVS_TAMPER5__GPIO5_IO05	0x80000000 /* MPUART1_DEN */
				MX6UL_PAD_SNVS_TAMPER6__GPIO5_IO06	0x80000000 /* MPUART1_RXEN */
			>;
		};

		pinctrl_uart8: uart8grp {
			fsl,pins = <
				MX6UL_PAD_LCD_DATA20__UART8_DCE_TX      0x1b0b1
				MX6UL_PAD_LCD_DATA21__UART8_DCE_RX      0x1b0b1
			>;
		};

		pinctrl_uart8_flow: uart8grp-1 {
			fsl,pins = <
				MX6UL_PAD_LCD_DATA20__UART8_DCE_TX      0x1b0b1
				MX6UL_PAD_LCD_DATA21__UART8_DCE_RX      0x1b0b1
				MX6UL_PAD_ENET2_RX_ER__UART8_DCE_RTS    0x80000000
				MX6UL_PAD_ENET2_TX_CLK__UART8_DCE_CTS   0x80000000
			>;
		};

		pinctrl_uart8_config: uart8grp-config {
			fsl,pins = <
				MX6UL_PAD_SNVS_TAMPER8__GPIO5_IO08	0x80000000 /* MPUART0_DEN */
				MX6UL_PAD_SNVS_TAMPER9__GPIO5_IO09	0x80000000 /* MPUART0_RXEN */
				MX6UL_PAD_CSI_MCLK__GPIO4_IO17		0x80000000 /* MPUART0_ON */
			>;
		};

Accessing the peripheralEdit

Linux messages at boot timeEdit

...
...
[    1.211906] 2020000.serial: ttymxc0 at MMIO 0x2020000 (irq = 30, base_baud = 5000000) is a IMX
[    1.962230] 2024000.serial: ttymxc7 at MMIO 0x2024000 (irq = 31, base_baud = 5000000) is a IMX
[    1.974074] 21e8000.serial: ttymxc1 at MMIO 0x21e8000 (irq = 65, base_baud = 5000000) is a IMX
[    1.985128] 21ec000.serial: ttymxc2 at MMIO 0x21ec000 (irq = 66, base_baud = 5000000) is a IMX
...
...

Usage with sttyEdit

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-lynx:~# stty -F /dev/ttymxc7 115200 -echo                                                                                                                                                          
root@desk-mx6ul-lynx:~# cat /dev/ttymxc7 &                                                                                                                                                                         
[1] 266
root@desk-mx6ul-lynx:~# echo "Test loopback" > /dev/ttymxc7
Test loopback

Additional informationEdit

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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