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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?
Parents
  • 0

    Hello,

    You are correct, 'pin control' was introduced in v2.0.0. However, it only controls the pin state. To get the UART to a low power state, you need to use it via the power management subsystem. The code snippet below shows an example of how you can use the API to power down your UART.

    prj.conf

    # Device power management
CONFIG_PM_DEVICE=y

    Code 

    #include <zephyr/pm/device.h>

...

void some_function(void) 
{
    int err;
    /* Power down the UART device */
    err = pm_device_action_run(<uart_dev>, PM_DEVICE_ACTION_SUSPEND);
    if (err) {
        printk("pm_device_action_run() failed (%d)\n", err);
    }
    
    ...
    /* Power it on again */
    err = pm_device_action_run(<uart_dev>, PM_DEVICE_ACTION_RESUME);
    if (err) {
        printk("pm_device_action_run() failed (%d)\n", err);
    }

    Best regards,

    Vidar

  • 0 in reply to Vidar Berg

    Sweet, I got it to compile! Will let you know. Big thanks!

  • 0 in reply to GameCodingNinja

    Assume you meant 0x00000002. Either way, if there is a problem with the pin configurations, you should see that when you measure the current draw.

  • 0 in reply to Vidar Berg

    This is working really well and we are getting the reduced power as per the datasheet.

    The next problem is I need to be able to restart the 52840 from the 9160. Spent a day trying to figure this out to no avail. Not sure what I need to do. Info online seems old and unrelated. Our 9160 pin 31 is what's connected to the 52840 pin 18 but not sure how to define that and activate it.

  • 0 in reply to GameCodingNinja

    The SDK examples enable the pinreset functionality on P0.18 by default (you can read the PSELRESET[n] register to confirm this). So, I assume the problem you're experiencing is with toggling of the IO from the 9160? 

    The bt_hci_transport_setup() function in https://github.com/nrfconnect/sdk-zephyr/blob/main/boards/arm/nrf9160dk_nrf9160/nrf52840_reset.c demonstrates one way you can assign a GPIO to control the reset line to the 52840.

    Example

    C code:

    #include <zephyr/drivers/gpio.h>

#define RESET_NODE DT_NODELABEL(nrf52840_reset)


#define RESET_GPIO_CTRL  DT_GPIO_CTLR(RESET_NODE, gpios)
#define RESET_GPIO_PIN   DT_GPIO_PIN(RESET_NODE, gpios)
#define RESET_GPIO_FLAGS DT_GPIO_FLAGS(RESET_NODE, gpios)

void reset_nrf52840(void)
{
	int err;
	const struct device *port = DEVICE_DT_GET(RESET_GPIO_CTRL);

	if (!device_is_ready(port)) {
		printk("nrf52840_reset is not ready\n");
	}

	/* Configure pin as output and initialize it to inactive state. */
	err = gpio_pin_configure(port, RESET_GPIO_PIN,
				 RESET_GPIO_FLAGS | GPIO_OUTPUT_INACTIVE);
	if (err) {
		printk("gpio_pin_configure() failed (err: %d)\n", err);
		return;
	}

	/* Assert the reset line */
	err = gpio_pin_set(port, RESET_GPIO_PIN, 1);
	if (err) {
		printk("gpio_pin_set() failed (err: %d)\n", err);
		return;
	}
    
    k_sleep(K_MSEC(10));

	/* Release reset line */
	err = gpio_pin_set(port, RESET_GPIO_PIN, 0);
	if (err) {
		printk("gpio_pin_set() failed (err: %d)\n", err);
		return;
	}

	printk("nrf52840 is reset\n");

}


void main(void)
{
	reset_nrf52840();
	...

    DTS overlay:

    &nrf52840_reset {
	status = "okay";
	gpios = <&gpio0 31 GPIO_ACTIVE_LOW>;
};

  • 0 in reply to Vidar Berg

    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");
}

  • 0 in reply to GameCodingNinja

    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.  

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