DESK-MX8M-L/Peripherals/UART

History
Version	Issue Date	Notes
1.0.0	Jan 2022	First DESK-MX8M release

Peripheral UART

Device tree configuration

Here below an example of device tree modifications to standard DAVE's kit for the ORCA SOM:

From imx8mp-mito8mplus.dtsi:

&uart4 {
        pinctrl-names = "default";
        pinctrl-0 = <&pinctrl_uart4>;
        assigned-clocks = <&clk IMX8MP_CLK_UART4>;
        assigned-clock-parents = <&clk IMX8MP_SYS_PLL1_80M>;
        fsl,uart-has-rtscts;
        status = "okay";
};

&iomuxc {
...
...
        pinctrl_uart4: uart4grp {
                fsl,pins = <
                        MX8MP_IOMUXC_ECSPI2_SCLK__UART4_DCE_RX    0x140
                        MX8MP_IOMUXC_ECSPI2_MOSI__UART4_DCE_TX    0x140
                        MX8MP_IOMUXC_ECSPI2_MISO__UART4_DCE_CTS   0x140
                        MX8MP_IOMUXC_ECSPI2_SS0__UART4_DCE_RTS    0x140
                >;
        };

Accessing the peripheral

Linux messages at boot time

...
...
[    0.755511] 30860000.serial: ttymxc0 at MMIO 0x30860000 (irq = 26, base_baud = 5000000) is a IMX
[    0.762356] 30880000.serial: ttymxc2 at MMIO 0x30880000 (irq = 27, base_baud = 5000000) is a IMX
[    0.771151] 30890000.serial: ttymxc1 at MMIO 0x30890000 (irq = 28, base_baud = 1500000) is a IMX
[    0.779648] printk: console [ttymxc1] enabled
[    0.798672] 30a60000.serial: ttymxc3 at MMIO 0x30a60000 (irq = 35, base_baud = 5000000) is a IMX
...
...
root@desk-mx8mp:~#

Usage with stty

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

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

root@desk-mx8mp:~# stty -F /dev/ttymxc3 115200 -echo
root@desk-mx8mp:~# cat /dev/ttymxc3 &
[2] 555
root@desk-mx8mp:~# echo "Test loopback" > /dev/ttymxc3
root@desk-mx8mp:~# 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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