How to put the UART to sleep (low power mode)

[GameCodingNinja]

I believe it started with SDK 2.0.0 but the board config files now define different ways to specify how hardware is to run.

&pinctrl {

    uart1_default: uart1_default {
		group1 {
			psels = <NRF_PSEL(UART_TX, 0, 26)>,
				<NRF_PSEL(UART_RTS, 0, 29)>;
		};
		group2 {
			psels = <NRF_PSEL(UART_RX, 0, 27)>,
				<NRF_PSEL(UART_CTS, 0, 28)>;
			bias-pull-up;
		};
	};

	uart1_sleep: uart1_sleep {
		group1 {
			psels = <NRF_PSEL(UART_TX, 0, 26)>,
				<NRF_PSEL(UART_RX, 0, 27)>,
				<NRF_PSEL(UART_RTS, 0, 29)>,
				<NRF_PSEL(UART_CTS, 0, 28)>;
			low-power-enable;
		};
	};
	
&uart1 {
	status = "okay";
	pinctrl-0 = <&uart1_default_alt>;
	pinctrl-1 = <&uart1_sleep_alt>;
	pinctrl-names = "default", "sleep";
};

I took this to mean that I can dynamically toggle these configurations from "uart1_default" to "uart1_sleep" from perhaps a function call. Did find the pinctrl_apply_state() function call but it's return a -2 that state id doesn't exist even though it is defined. Here's my code.

uart = device_get_binding("UART_1");

int err = pinctrl_apply_state(uart->config, PINCTRL_STATE_SLEEP); // Returns -2

Any ideas?

[GameCodingNinja]

I was able to code it out. Looks to be working. These crazy macro will be the death of me.

void ble_reset()
{
    if(!device_is_ready(gpio_dev))
    {
		LOG_ERR("nrf52840_reset is not ready");
        return;
	}

    // Configure pin as output and initialize it to inactive state.
	int err = gpio_pin_configure(gpio_dev, GPIO_BLE_RESET_PIN, 0 | GPIO_OUTPUT_INACTIVE);
	if(err)
    {
		LOG_ERR("gpio_pin_configure() failed (err: %d)", err);
		return;
	}

    // Assert the reset line
	err = gpio_pin_set(gpio_dev, GPIO_BLE_RESET_PIN, 1);
	if(err)
    {
		LOG_ERR("gpio_pin_set() failed (err: %d)", err);
		return;
	}
    
    k_sleep(K_MSEC(10));

	// Release reset line
	err = gpio_pin_set(gpio_dev, GPIO_BLE_RESET_PIN, 0);
	if(err)
    {
		LOG_ERR("gpio_pin_set() failed (err: %d)", err);
		return;
	}

	printk("nrf52840 is reset\n");
}

[Vidar Berg]

Excellent, thanks for the update. Regarding the macro errors, if you have the time, there was a great talk about this topic by Marti at the Zephyr developer summit where he explains the "macrobatics," as he called it. Link to the recording if you are interested: https://www.youtube.com/watch?v=w8GgP3h0M8M.  

[GameCodingNinja]

I wasn't able to get past the macro errors which is why I coded it. Thanks for the video. I now understand why macros are used but I'll need to watch the video a few times. macros to this degree is very complicated. Would like to understand it better.

Thanks got all your help! I greatly appreciate it!

[Vidar Berg]

I agree it's complicated (when it doesn't work). But I think I know why it did not work for you. I was building for the 'nrf9160dk_nrf9160' board which includes the device tree binding for 'nrf52840_reset' node: https://github.com/nrfconnect/sdk-zephyr/commit/71223ad0d0e6f152912f314ea2df3fa656995bb6 . This may not be included if you have created a custom board.