Uart3's Rx pin is not working with imx8 Nano evk board

[shilesh_babu]

Dear NXP,

I am using uart3 for a serial communication, for testing i am connecting serial-usb converter to send some data from my laptop to Nano board uart for debugging propose only.

from the evk board side i am sending this data 

$echo "testing" >> /dev/ttymxc2 

and on the laptop side receiving this 

$cat /dev/ttyUSB2

$testing

from laptop side  

$echo "testing" >>  /dev/ttyUSB2  

and on the evk board side receiving nothing............. 

$cat /dev/ttymxc2

so it means only Tx pin is working on the evk board side, Rx is not working.

Even if i check in uart loop-back, nothing is showing on evk terminal, is this can be the kernel issue.

$uname -a

5.4.24-2.1.0+gbabac008e5cf #1 SMP PREEMPT Mon Jul 27 19:49:53 UTC 2020 aarch64 aarch64 aarch64 GNU/Linu

Best Regards,

S Babu

[weidong_sun]

Hello shilesh,

Below is from device tree in L5.4.24_2.1.0:

...

        pinctrl_uart3: uart3grp {
            fsl,pins = <
                MX8MN_IOMUXC_ECSPI1_SCLK_UART3_DCE_RX        0x140
                MX8MN_IOMUXC_ECSPI1_MOSI_UART3_DCE_TX        0x140
                MX8MN_IOMUXC_ECSPI1_SS0_UART3_DCE_RTS_B        0x140
                MX8MN_IOMUXC_ECSPI1_MISO_UART3_DCE_CTS_B    0x140
            >;
        };

....

It means that you will used ECSPI1_SCLK pin and ECSPI1_MOSI pin to connect PC via UART to USB bridge.

Connections like below:

ECSPI1_SCLK(DCE_RX)------->TX of UART_TO_USB BRIDGE---->PC USB

ECSPI1_MOSI(DCE_TX)------->RX of UART_TO_USB BRIDGE---->PC USB

BUT you should pay attention to UART3 node in device tree:  RTS_B & CTS_B are supported, which means communications via UART3 will use Hardware Flow Control.

......

&uart3 {
    pinctrl-names = "default";
    pinctrl-0 = <&pinctrl_uart3>;
    assigned-clocks = <&clk IMX8MN_CLK_UART3>;
    assigned-clock-parents = <&clk IMX8MN_SYS_PLL1_80M>;
    fsl,uart-has-rtscts;
    status = "okay";
};

......

So if you want to used it , you have 2 ways like below:

(1) Disabling RTS & CTS

Remove the line from above node:

 /*fsl,uart-has-rtscts;*/

(2) Using Hardware Flow Control for your test

In DCE mode:

RTS_B is input:  it should be connected to CTS_B of UART_TO_USB BRIDGE.

CTS_B is output: it should be connected to RTS_B of UART_TO_USB BRIDGE.

Hope above information is helpful to you!

Have a nice day!

B.R,

Weidong

[shilesh_babu]

Hi Wigros Sun, 

thanks for your support, but after doing all these changes facing the same issue uart rx pin is not working.....

My device tree configuration for uart3 is 

&uart3 {

        pinctrl-names = "default";

        pinctrl-0 = <&pinctrl_uart3>;

        /assigned-clocks = <&clk IMX8MN_CLK_UART3>;

        assigned-clock-parents = <&clk IMX8MN_SYS_PLL1_80M>;

        /* fsl,uart-has-rtscts; */ //commented this line

        status = "okay";

};

 what can be the issue ??

[weidong_sun]

Hello shilesh,

You can also test it with loopback.
1. Pin7 & Pin11 are connected together.
2. Pin 8 & Pin10 are connected togeter.
3. Writing a simple app with hardware flow control function.

J1003 on i.MX8MN-EVK board is interface for Raspberry Pi Module B+ , UART3 has been tested.

Have  a nice day!

B.R,

Weidong