Storing variable values in system off mode.

[Anand Ramashetty]

Hi,

I need to store few variables values(long a = 4568;) to RAM (might be some other place) when the system went to sytem off mode .

How I can achieve in the nRF 51822 version 3.1 controller with SDK 6 and SD S110 .

Regards, Anand

[Susheel Nuguru]

Hi Anand,

I am assuming that you are asking on how to put RAM in retention mode just before system off.

// Switch on both RAM banks when in System OFF mode.
NRF_POWER->RAMON |= (POWER_RAMON_OFFRAM0_RAM0On << POWER_RAMON_OFFRAM0_Pos) | 
                    (POWER_RAMON_OFFRAM1_RAM1On << POWER_RAMON_OFFRAM1_Pos);

// Enter System OFF and wait for wake up from GPIO detect signal.
NRF_POWER->SYSTEMOFF = 0x1;

This will put both the RAM banks into retention and your stored values in ram will retain their values after the system wakes up from OFF mode.

I would also recommend you to use latest SDK available for your projects. developer.nordicsemi.com/.../

Also do not initialize RAM at every system restart

[Susheel Nuguru]

static void display_failure(void) { while (true) { LEDS_INVERT(LEDS_MASK); nrf_delay_ms(1000); } }

void HardFault_Handler()
{
		display_failure();
    LEDS_ON(LEDS_MASK);

    // Loop forever.
    while (true)
    {
 
    }
}

int main(void)
{
		uint8_t ManufacturerData[30] ;
		uint32_t count = 0;
		uint8_t * p_ram_test;	
		
		p_ram_test = (uint8_t *)&ManufacturerData[0];
    LEDS_CONFIGURE(LEDS_MASK);
    LEDS_OFF(LEDS_MASK);

    // This pin is used for waking up from System OFF and is active low, enabling sense capabilities.
    nrf_gpio_cfg_sense_input(PIN_GPIO_WAKEUP, BUTTON_PULL, NRF_GPIO_PIN_SENSE_LOW);
	
    // Workaround for PAN_028 rev1.1 anomaly 22 - System: Issues with disable System OFF mechanism
    nrf_delay_ms(1);

    // Check if the system woke up from System OFF mode by reading the NRF_POWER->GPREGRET register which has
    // retained the value written before going to System OFF. Below is the layout for usage for
    // NRF_POWER->GPREGRET register.
    //  BITS |   7   |   6   |   5   |   4   |   3   |   2   |   1   |   0
    //  --------------------------------------------------------------------
    //       |        SPECIAL_SEQUENCE       
    //  --------------------------------------------------------------------
    ///

    if (NRF_POWER->GPREGRET  == RESET_MEMORY_TEST_BYTE)
    {
			// We can be here only after we woken up from system off after pressing the button.
			// clear GPREGRET register before exit.
			NRF_POWER->GPREGRET = 0;

			for(count = 0; count < sizeof(ManufacturerData); count++)
			{
				if(*p_ram_test++ != count)
				{
					display_failure();	// This means the contents of RAM were not the same that we wrote just before system off
				}
			}

			LEDS_ON(1 << SUCCESS_PIN_NUMBER); // RAM retention worked for our variable
			
			while (true)
			{
					// Do nothing.
			}
    }

    // Write the known sequence to the GPREGRET register.
    NRF_POWER->GPREGRET = RESET_MEMORY_TEST_BYTE;

    // Write the known value to the known address in RAM, enable RAM retention, set System OFF, and wait
    // for GPIO wakeup from external source.

    LEDS_ON(1 << READY_PIN_NUMBER);
    nrf_delay_ms(1000);

    // Switch on both RAM banks when in System OFF mode.
    NRF_POWER->RAMON |= (POWER_RAMON_OFFRAM0_RAM0On << POWER_RAMON_OFFRAM0_Pos) |
                        (POWER_RAMON_OFFRAM1_RAM1On << POWER_RAMON_OFFRAM1_Pos);

		// Write a sequence of numbers to the RAM addresses to be tested
		for(count = 0; count < sizeof(ManufacturerData); count++)
		{
			*p_ram_test++ = count;
		}
					

    // Enter System OFF and wait for wake up from GPIO detect signal.
    NRF_POWER->SYSTEMOFF = 0x1;

		while(1);	// This is useful to debug systemoff mode

}