Is there a way to setup device tree to use a pin for UART and as GPIO?

[denis]

I am interfacing with a part that uses the same pin, P0.6, for two purposes:

1) The pin is used for UART communication.  MCU RX input.

2) The pin is used as a GPIO.  MCU GPIO output.

I am using runtime power management.  What I would like is that when the UART driver is in the default state then the pin is connected to the UART.  When the UART driver is in the sleep state then the pin is used as a GPIO.  Is this possible?

What I have right now in my dts as a (incorrect) starting point is:

arduino_serial: &uart0 {

  pinctrl-0 = <&uart0_default>;

  pinctrl-1 = <&uart0_sleep>;

  pinctrl-names = "default", "sleep";

...

};

 

uart0_default: uart0_default {

  group1 {

    psels = <NRF_PSEL(UART_RX, 0, 6)>;

    bias-pull-up;

  };

  group2 {

    psels = <NRF_PSEL(UART_TX, 0, 20)>;

  };

};

uart0_sleep: uart0_sleep {

  group1 {

    psels = <NRF_PSEL(UART_RX, 0, 6)>, <NRF_PSEL(UART_TX, 0, 20)>;

    low-power-enable;

  };

};

interface_ctl {

  compatible = "gpio-leds";

  uart_log_txd: uart_log_txd {

    gpios = <&gpio0 6 GPIO_PULL_UP>;

    label = "UART LOG TXD";

  };

};

[Vidar Berg]

Hello,

This should not be a problem as long you make sure to suspend the UART driver through the power management API before you re-configure the RX pin.

Best regards,

Vidar

[denis]

Won't putting the uart to sleep, with the dts above, still retain control of P0.6?

Is there a way, via the dts, to have the uart not retain control of P0.6 when to goes to sleep?  Some dts NRF constant for no connection?

Seems like the pin control API is meant to do this kind of thing in a portable manner.  I read through the docs online, but still a bit unclear to me how the pin control API is intended to be used for this specific type of situation.

[Vidar Berg]

Yes, the pin assignments are retained in the peripheral registers after you have run the PM_DEVICE_ACTION_SUSPEND action. But this action will also disable and power down the UARTE (the power down sequence is outlined in the Low power section of the UARTE chapter). Thus, freeing the UART pins.

pinctrl currently does not provide a way to clear the PSEL registers.