RAM retention failure

Question

Hello 
 I am trying to figure out the ram retention on my nRF52-DK using SES and SDK v17.1.0. I've run through the example ram_retention , and studied a topic in Nordic's documentation, as well as a couple of threads here in DevZone, like this one , and this one . I adapted my code to implement RAM retention using the given examples, but it didn't work for me. 
 I did all the mentioned steps: 
 
 declared the variable I want to retain in the .non_init section ( static uint32_t ble_activate __attribute__((section(".non_init"))); ) 
 turned the RAM powered on during the SystemOFF sleepmode: // Configure the RAM retention parameters
uint8_t i;
for(i = 0; i < 8; i++) // Retain RAM 0 - RAM 7
{
 sd_power_ram_power_set(i, (POWER_RAM_POWER_S0POWER_On << POWER_RAM_POWER_S0POWER_Pos) |
 (POWER_RAM_POWER_S1POWER_On << POWER_RAM_POWER_S1POWER_Pos) |
 (POWER_RAM_POWER_S0RETENTION_On << POWER_RAM_POWER_S0RETENTION_Pos) |
 (POWER_RAM_POWER_S1RETENTION_On << POWER_RAM_POWER_S1RETENTION_Pos));
}
// Delay for one second 
nrf_delay_ms(1000); 
 And checking up the NRF_POWER->GPREGRET for a pre-set value upon every wakeup. 
 
 However, I see that value is not preserved since I am outputting it using printf and it returns back as a nonsense number. Please, find my main.c attached. The crucial steps are implemented in void mers_ram_retention(void) . The code is loosely based on ble_app_uart example, that is, in configures BLE stack as per original method and then starts advertising, and finally, goes to SystemOFF. 
 
 Could you please tell me what went wrong? 
 Best, 
 W

user4240 · Accepted Answer

Excellent 
 user74012 said: Is that a right way to do things here? Check the variable in RAM, and turn the BLE depending on it? 
 Yes, this will work. 
 user74012 said: Can you tell me how to find out where my variable actually is, and how to pick a proper RAM region accordingly? 
 You can see where the .non_init section is located in RAM from the memory usage view in SES here (or from the *.map output): 
 
 And when you know the address, you can look up the which RAM slave and section it belongs to by referring to figure 1 in the Memory chapter of the PS. Each 4K section consumes about 30 nA when retention is enabled. 
 Important: the .non_init section does not start at a fixed address. So it may change between builds. E.g. when you turn off or enable compiler optimization.

RAM retention failure

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