How-To use UART7/8 on i.MX6UL

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How-To use UART7/8 on i.MX6UL

How-To use UART7/8 on i.MX6UL

       There are 8 UART ports on i.mx6ul and one uniform Linux driver for these UARTs. Form UART1~UART6, there is no special operation or attention to use them. But for UART7/UART8, there is a special rule to enable them.

      According to i.mx6ul RM, we can see UART7/8 RTS pins are muxed with ENET TX_CLK pins. When SION bit of ENET_TX_CLK is set, we need switch to other MUX mode as input signal for UARTx_RTS. Otherwise, UARTx_RTS will be interrupted by loopback ENET clock signal. So we should set IOMUXC_UART7_RTS_B_SELECT_INPUT and IOMUXC_UART8_RTS_B_SELECT_INPUT registers to 0x2/03 to avoid ENET clock's conflict no matter whether we enable UART7/8 RTS/CTS function or not.

Let's summarize the different scenarios to enable UART7/8 as follows:

1. ENET driver is disabled and UART7/8 is enabled. There is no special operation to do, just use UART7/8 like other UARTs

2. ENET and UART7/8 are both enabled. There are two use models, RTS/CTS enabled or disabled.

    2a. If we enable RTS/CTS feature and configure RTS/CTS pins in the device tree, of course, we should avoid the conflict between UART CTS/RTS pins and ENET TX_CLK pins. There is no special operation to do becuase your RTS/CTS device tree would automatically set  IOMUXC_UART7_RTS_B_SELECT_INPUT/ IOMUXC_UART8_RTS_B_SELECT_INPUT register to correct value.

    2b. If we don't enable RTS/CTS feature and no RTS/CTS pin configuration in devcie tree, we should manually add code to set  IOMUXC_UART7_RTS_B_SELECT_INPUT/  IOMUXC_UART8_RTS_B_SELECT_INPUT register because the default value is 0x0(ENETx_TX_CLK_ALT1)

Here is an example to show how to use UART7 on EVK board in scenario 2b.

1. modify imx6ul-14x14-evk.dts to enable UART7

    a. remove all  LCD settings to disable lcdif because we configure UART7 TX/RX pin pad to LCD data line

    b. add UART7 related settings

               &uart7 {

                    pinctrl-names = "default";

                    pinctrl-0 = <&pinctrl_uart7>;

                   status = "okay";

                };

              &iomuxc {

                  pinctrl-names = "default";

                  pinctrl-0 = <&pinctrl_hog_1>;

                  ....

                          pinctrl_uart7: uart7grp {

                          fsl,pins = <

                                      MX6UL_PAD_LCD_DATA16__UART7_DCE_TX 0x1b0b1

                                      MX6UL_PAD_LCD_DATA17__UART7_DCE_RX 0x1b0b1

                          >;

                 };

2. add code to set IOMUXC_UART7_RTS_B_SELECT_INPUT register in arch/arm/mach-imx/mach-imx6ul.c


         static void __init imx6ul_init_machine(void)

         {

              struct device *parent;

              void __iomem *iomux;

              struct device_node *np;

              ...........

              imx6ul_pm_init();

              np = of_find_compatible_node(NULL,NULL,"fsl,imx6ul-iomuxc");

              iomux = of_iomap(np, 0);

              writel_relaxed(0x2,iomux+0x650);

           }

3. build zImage and imx6ul-14x14-evk.dtb

4. Test in linux console

     root@imx6ulevk: ls /dev/ttymxc*                      //you can see ttymxc6 is in the list

    root@imx6ulevk: echo hello > /dev/ttymxc6    

    root@imx6ulevk:

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thanks your infomation.

but we want to use the

pinctrl_uart7: uart7grp {

                        fsl,pins = <

                              MX6UL_PAD_ENET2_RX_EN__UART7_DCE_TX     0x1b0b1

                              MX6UL_PAD_ENET2_TX_DATA0__UART7_DCE_RX  0x1b0b1

                        > ;

                };

and disable the ENET2 , we already done that .

but it seemed no TX out signal , i don't know why , could you help me with that , thank you .

Thank you for posting this information. I have a really simple question that I can't seem to find the answer too. How do I build imx6ul-14x14-evk.dtb? I modify the dts and attempt to "make" but it never rebuilds. Can you please enlighten me. I'm new to all of this.  

Thank you for posting this information.You mean the LCD and uart7/8 conflict?

Hi Sir,

We are not using LCD but wants to use both Ethernets and UART7 and UART8. I followed your steps.

UART7 is working but UART8 is not working. When I echo on UART8 , board hangs.

Please let me know what could be wrong .... We are stuck .. Please help ...

As per the instructions if we are using UART7/UART8 CTS/RTS in DTS nothing needs to be added in the code.

I have also tried adding the below lines

writel_relaxed(0x3, iomux + 0x650);
writel_relaxed(0x3, iomux + 0x658);

UART7 and UART8 DTS IO MUXING..

&uart7 {
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_uart7>;
fsl,uart-has-rtscts;
linux,rs485-enabled-at-boot-time;
status = "okay";
};

&uart8 {
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_uart8>;
fsl,uart-has-rtscts;
linux,rs485-enabled-at-boot-time;
status = "okay";
};

pinctrl_uart7: uart7grp {
fsl,pins = <
MX6UL_PAD_LCD_DATA16__UART7_DCE_TX 0x0001B0B1
MX6UL_PAD_LCD_DATA17__UART7_DCE_RX 0x0001B0B1
MX6UL_PAD_LCD_DATA06__UART7_DCE_CTS 0x0001B0B1
MX6UL_PAD_LCD_DATA07__UART7_DCE_RTS 0x0001B0B1
>;
};

pinctrl_uart8: uart8grp {
fsl,pins = <
MX6UL_PAD_LCD_DATA20__UART8_DCE_TX 0x0001B0B1
MX6UL_PAD_LCD_DATA21__UART8_DCE_RX 0x0001B0B1
MX6UL_PAD_LCD_DATA04__UART8_DCE_CTS 0x0001B0B1
MX6UL_PAD_LCD_DATA05__UART8_DCE_RTS 0x0001B0B1
>;
};

Hi,
your answer was helpful but I am stuck on a particular region.
I have a Connect Core 6UL SBC Express board. I want to enable the other UARTs.
UART 4 is enabled on the expansion connector and UART 5 is routed to console.
I want to enable any other UARTs.

Thanks in advance.

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Last update:
‎01-06-2016 07:44 PM
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