RAM retention failure

[Pero Krivic]

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. 

Fullscreen 2086.main.c Download

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 */

#include <stdint.h>
#include <string.h>
#include "app_timer.h"
#include "bsp_btn_ble.h"
#include "nrf_pwr_mgmt.h"

#if defined (UART_PRESENT)
#include "nrf_uart.h"
#endif
#if defined (UARTE_PRESENT)
#include "nrf_uarte.h"
#endif

#include "nrf_log.h"
#include "nrf_log_ctrl.h"
#include "nrf_log_default_backends.h"
#include "nrf_delay.h"

#include "MERS_BLE.h"
#include "MERS_LoRaWAN.h"
#include "MERS_fstorage.h"


/* Project global variables */
extern uint8_t key_cnt;
extern bool keys_received;
extern bool ble_connected;
static uint32_t ble_activate __attribute__((section(".non_init")));


/**@brief Function for initializing the timer module.
 */
static void timers_init(void){
    ret_code_t err_code = app_timer_init();
    APP_ERROR_CHECK(err_code);
}



/**@brief Function for handling events from the BSP module.
 *
 * @param[in]   event   Event generated by button press.
 */
void bsp_event_handler(bsp_event_t event){
    uint32_t err_code;
    switch (event)
    {
        case BSP_EVENT_SLEEP:
            sleep_mode_enter();
            break;

        case BSP_EVENT_DISCONNECT:
            //err_code = sd_ble_gap_disconnect(m_conn_handle, BLE_HCI_REMOTE_USER_TERMINATED_CONNECTION);
            //if (err_code != NRF_ERROR_INVALID_STATE)
            //{
            //    APP_ERROR_CHECK(err_code);
            //}
            break;

        case BSP_EVENT_WHITELIST_OFF:
            //if (m_conn_handle == BLE_CONN_HANDLE_INVALID)
            //{
            //    err_code = ble_advertising_restart_without_whitelist(&m_advertising);
            //    if (err_code != NRF_ERROR_INVALID_STATE)
            //    {
            //        APP_ERROR_CHECK(err_code);
            //    }
            //}
            break;

        default:
            break;
    }
}

/**@brief   Function for handling app_uart events.
 *
 * @details This function will receive a single character from the app_uart module and append it to
 *          a string. The string will be be sent over BLE when the last character received was a
 *          'new line' '\n' (hex 0x0A) or if the string has reached the maximum data length.
 */
/**@snippet [Handling the data received over UART] */
void uart_event_handle(app_uart_evt_t * p_event){
    static uint8_t data_array[BLE_NUS_MAX_DATA_LEN];
    static uint8_t index = 0;
    uint32_t       err_code;

    switch (p_event->evt_type)
    {
        case APP_UART_DATA_READY:
            UNUSED_VARIABLE(app_uart_get(&data_array[index]));
            index++;

            //if ((data_array[index - 1] == '\n') ||
            //    (data_array[index - 1] == '\r') ||
            //    (index >= m_ble_nus_max_data_len))
            //{
            //    if (index > 1)
            //    {
            //        NRF_LOG_DEBUG("Ready to send data over BLE NUS");
            //        NRF_LOG_HEXDUMP_DEBUG(data_array, index);

            //        do
            //        {
            //            uint16_t length = (uint16_t)index;
            //            err_code = ble_nus_data_send(&m_nus, data_array, &length, m_conn_handle);
            //            if ((err_code != NRF_ERROR_INVALID_STATE) &&
            //                (err_code != NRF_ERROR_RESOURCES) &&
            //                (err_code != NRF_ERROR_NOT_FOUND))
            //            {
            //                APP_ERROR_CHECK(err_code);
            //            }
            //        } while (err_code == NRF_ERROR_RESOURCES);
            //    }

            //    index = 0;
            //}
            break;

        case APP_UART_COMMUNICATION_ERROR:
            APP_ERROR_HANDLER(p_event->data.error_communication);
            break;

        case APP_UART_FIFO_ERROR:
            APP_ERROR_HANDLER(p_event->data.error_code);
            break;

        default:
            break;
    }
}
/**@snippet [Handling the data received over UART] */



/**@brief  Function for initializing the UART module.
 */
/**@snippet [UART Initialization] */
static void uart_init(void){
    uint32_t                     err_code;
    app_uart_comm_params_t const comm_params =
    {
        .rx_pin_no    = RX_PIN_NUMBER,
        .tx_pin_no    = TX_PIN_NUMBER,
        .rts_pin_no   = 0,
        .cts_pin_no   = 0,
        .flow_control = APP_UART_FLOW_CONTROL_DISABLED,
        .use_parity   = false,
#if defined (UART_PRESENT)
        .baud_rate    = NRF_UART_BAUDRATE_115200
#else
        .baud_rate    = NRF_UARTE_BAUDRATE_115200
#endif
    };

    APP_UART_FIFO_INIT(&comm_params,
                       UART_RX_BUF_SIZE,
                       UART_TX_BUF_SIZE,
                       uart_event_handle,
                       APP_IRQ_PRIORITY_LOWEST,
                       err_code);
    APP_ERROR_CHECK(err_code);
}
/**@snippet [UART Initialization] */



/**@brief Function for initializing buttons and leds.
 *
 * @param[out] p_erase_bonds  Will be true if the clear bonding button was pressed to wake the application up.
 */
static void buttons_leds_init(bool * p_erase_bonds){
    bsp_event_t startup_event;

     uint32_t err_code = bsp_init(BSP_INIT_LEDS | BSP_INIT_BUTTONS, bsp_event_handler);
     APP_ERROR_CHECK(err_code);

     err_code = bsp_btn_ble_init(NULL, &startup_event);
     APP_ERROR_CHECK(err_code);

    *p_erase_bonds = (startup_event == BSP_EVENT_CLEAR_BONDING_DATA);
}


/**@brief Function for initializing the nrf log module.
 */
static void log_init(void){
    ret_code_t err_code = NRF_LOG_INIT(NULL);
    APP_ERROR_CHECK(err_code);

    NRF_LOG_DEFAULT_BACKENDS_INIT();
}


/**@brief Function for initializing power management.
 */
static void power_management_init(void){
    ret_code_t err_code;
    err_code = nrf_pwr_mgmt_init();
    APP_ERROR_CHECK(err_code);
}


/**@brief Function for handling the idle state (main loop).
 *
 * @details If there is no pending log operation, then sleep until next the next event occurs.
 */
static void idle_state_handle(void){
    if (NRF_LOG_PROCESS() == false)
    {
        nrf_pwr_mgmt_run();
    }
}


/**@brief A function to fetch LoRaWAN keys
*/
mers_ble_keys_t mers_ble_obtain_keys(void){
    /* Check if the LoRa keys have been received and store them in the Flash */
    if (keys_received){
        NRF_LOG_INFO("Received 4 keys.");
        NRF_LOG_FLUSH();
        mers_store_lora_keys();
        ble_activate = false;
        /* Keys are received, we can disconnect and disable BLE */
        //mers_ble_disconnect();       // <--- Leave the disconnect decision to the Smartphone 
        ble_connected = false;
        return MERS_KEYS_RECEIVED_OK;
    }
    else
        return MERS_KEYS_RECEIVED_NOT_OK;
}


void mers_ram_retention(void){
    // Check if chip is waking up after a SoftReset.
    if(NRF_POWER->GPREGRET == 0xBB){  
        printf("\n\rble_activate value: %d", ble_activate);
        // Reset GPREGRET register
        // NRF_POWER->GPREGRET = 0x00;        
    }
    else {
        ble_activate = 0x01UL;            
        // Store magic number in GPREGRET register to indicate that the content should be checked upon reset. 
        NRF_POWER->GPREGRET = 0xBB;
    }

    // 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);
}


/**@brief Application main function.
 */
int main(void){

    bool erase_bonds;

    // Initialize.
    uart_init();
    log_init();
    timers_init();
    buttons_leds_init(&erase_bonds);
    power_management_init();
    fstorage_init();

    // Start execution.
    printf("\n\r*********************************");
    printf("\n\r       MarineEye Remote Sensor"   );
    printf("\n\r          Pero, 2022"             );
    printf("\n\r*********************************");
    /*
        Add Git version printout 
    */
    NRF_LOG_INFO("Debug logging for MERS over RTT started.");
    NRF_LOG_FLUSH();
    
    mers_ram_retention();
    printf("\n\rble_activate value: %d", ble_activate);
    printf("\n\rkeys_received value: %d", keys_received);

    /* Activate the BLE radio and start advertising */
    if (ble_activate){
        mers_ble_init();
        printf("\n\rBLE Advertising started.\n\r");
    }
    else{
        printf("\n\rBLE not activated.");
    }
    
    ///* Check for the keys in the Flash */
    //if (mers_read_lora_keys() != LORA_KEYS_IN_FLASH_OK){   

    //      ble_activate = true;
    //      /* Activate BLE radio and get the keys */
    //      mers_ble_obtain_keys();      
    //}
    //else{
    //    NRF_LOG_INFO("\n\rLoRaWAN Keys found.\n\rBLE radio not started.");
    //    /*
    //    Do the job with Lora keys
    //    */
    //}

    //NRF_LOG_INFO("\n\rDevice going to sleep");
    //NRF_LOG_FLUSH();
    uint32_t dummy_cntr = 0;

    while(1){

        if (ble_connected){
            if(mers_ble_obtain_keys() == MERS_KEYS_RECEIVED_OK){
                printf("\n\rLoRaWAN Keys received.");
                sleep_mode_enter();
            }
            ble_activate = 0UL;
        }
        else{
            dummy_cntr++;
            if ((dummy_cntr % 40) == 0)
                printf("\n\rble_activate value: %d", ble_activate);
        }
        
        idle_state_handle();
    }
}


/**
 * @}
 */

Could you please tell me what went wrong?

Best, 

W

[Vidar Berg]

Hello,

The RAM configuration looks to be correct. However, when the noinit section gets corrupted it usually is because there is a bootloader overwriting the section on startup. Could that be the case here? If not, I will try to set up a test tomorrow and see if I can replicate the issue on my side.

Best regards,

Vidar

[Pero Krivic]

Hello Vidor, thanks for the reply. I'm not using the bootloader, as far as I know. I have started from ble_app_uart and built upon it, never including any bootloader. 

Hey, if it helps, I have uploaded you a complete project -  I've stripped down all functionality except ble-uart and ram retention to demonstrate the issue. It should run on PCA10040:

MERS.zip

Best, P

[Pero Krivic]

Hey Vidar, this has worked out! Thanks man, you're awesome!

I've taken your approach with NRF_POWER->RAM[i].POWERSET functions, since I turn SoftDevice on, only after the RAM retention is set, and only if the variable retained in RAM checks out. Is that a right way to do things here? Check the variable in RAM, and turn the BLE depending on it?

Second, I feel it's kinda waste of power to turn on all of the RAM regions, since my 4-byte variable resides only in one of them. Can you tell me how to find out where my variable actually is, and how to pick a proper RAM region accordingly?

Best, 

P

[Vidar Berg]

Excellent

Pero Krivic 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.

Pero Krivic 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.

[Pero Krivic]

Vidar Berg said:

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):

Can you believe, I did exaxtly that last night? I found out that my variable lives at 0x20003F00, i.e in the section RAM 1. When I turned off all sections except that one, it worked just fine! How cool is that?

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.

This is what I also noticed. Is there a way to fix a variable at the given section and make sure it stays there every time?

[Vidar Berg]

Yes, you can specify a fixed start address for the non_init section in your flash_placemecement.xml file.

e.g.

Note that this fixed address must be somewhere between .tbss and   .heap (or .stack if you don't use heap).

[Pero Krivic]

Cool. One last question: in short words, how does the compiler (linker?) determine the addresses of all those sections? I always though it was pregiven in the .ld file (though I never bothered to look it up there)

[Vidar Berg]

The linker starts with the first sections and sequentially works its way up one section at a time. So the start address of a section is usually dependent on the size of previous sections. You may, for instance, notice that .non_init gets shifted up when you add more static zero initialized variables in your code (placed in .bss)

SES generates the actual linker script from the flash_placement.xml file. The generated linker script can be found together with the other output files.

[Pero Krivic]

Awesome! Thanks Vidar!