Enable RTS on UARTC PIN 4

Technical Support
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1

I need to activate altenernate function RTS UART C on PIN 4 IMX6ULL, I’m already using ovelays to activate autodirection on all the uarts, a and b are ok but uartc works but doesn’t have rts pin on PIN 4.

&uart1 {
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_uart1>;
	fsl,uart-has-rtscts;
	fsl,dte-mode;
	linux,rs485-enabled-at-boot-time;
        rs485-rts-active-low;
	status = "okay";
};
&uart2 {
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_uart2>;
	fsl,uart-has-rtscts;
	fsl,dte-mode;
	linux,rs485-enabled-at-boot-time;
        rs485-rts-active-low;
	status = "okay";
};
&uart5 {
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_uart5>;
	fsl,uart-has-rtscts;
	fsl,dte-mode;
	linux,rs485-enabled-at-boot-time;
        rs485-rts-active-low;
	status = "okay";
};
2

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To activate the RTS function for UART C (which corresponds to &uart5 in the device tree for the i.MX6ULL) on PIN 4, you will need to ensure that the pin is correctly configured in the device tree to support RTS functionality. Given that UART A and B are configured and working with RTS, but UART C does not have RTS on PIN 4 as per your description, the issue likely lies in the pin configuration for UART C.

First, verify that PIN 4 is capable of serving as an RTS pin for UART C on the i.MX6ULL. This information can be found in the i.MX6ULL reference manual, which details the pin multiplexing options available. If PIN 4 can indeed function as RTS for UART C, you will need to adjust the pin control settings (pinctrl-0) for &uart5 to include this pin with the correct alternate function setting.

The device tree snippet you provided for &uart5 shows the configuration for enabling RS-485 mode, including RTS/CTS hardware flow control (fsl,uart-has-rtscts;). However, to specifically assign PIN 4 for RTS functionality, you’ll need to define a pin control group (pinctrl) that includes PIN 4 configured for the RTS function. This involves creating or modifying a pin control group in the pinmux settings.

Here is a generalized example of what the pin control group definition might look like, assuming PIN 4 is designated as MX6ULL_PAD_xxx for RTS functionality:

&pinctrl {
    uart5rtsgrp: uart5rtsgrp {
        fsl,pins = <
            MX6ULL_PAD_xxx MX6_PAD_SETTINGS_UART_RTS
        >;
    };
};

&uart5 {
    pinctrl-names = "default";
    pinctrl-0 = <&pinctrl_uart5 &uart5rtsgrp>;
    fsl,uart-has-rtscts;
    fsl,dte-mode;
    linux,rs485-enabled-at-boot-time;
    rs485-rts-active-low;
    status = "okay";
};

In this example, MX6ULL_PAD_xxx should be replaced with the actual pad definition for PIN 4 configured for the RTS function, and MX6_PAD_SETTINGS_UART_RTS should be replaced with the correct pad settings for RTS functionality. These settings typically include the mux mode, pull-up/pull-down configuration, and any

Please, also check if these links can help you solve your problem:

Pin Multiplexing - Changing Pin Functionalities in the Linux Device Tree | Toradex Developer Center.

3

In the datasheet PIN 4 alt function 8 I have uart5.rts_b but I don’t find the names in the overlay
pin 4 is MX6UL_PAD_GPIO1_IO08__GPIO1_IO08 but RTS?

&pinctrl {
uart5rtsgrp: uart5rtsgrp {
fsl,pins = <
MX6UL_PAD_GPIO1_IO08__GPIO1_IO08 MX6UL_PAD_SETTINGS_UART_RTS
>;
};
};

4

Hi @fabrizio.camagna

Try MX6UL_PAD_GPIO1_IO08__UART5_DCE_RTS