SDK12.2 Secure DFU Timeout

[WestCoastDaz]

I want to add a timeout to the secure DFU bootloader if I enter it from the application. I found this post here devzone.nordicsemi.com/.../ but unfortuately I can't use the WDT because my application is using it with a quick timeout. What's the best way to a timeout using the app_timer module?

Cheers, Darren

[bjorn-spockeli]

You are correct, the WDT cannot be re-configured once it has been started. Using the app_timer module for this is overkill, I suggest using the RTC driver instead and then resetting the counter everytime the bootloader is handling a request.

In order to do this you have to add the following snippets to nrf_dfu.c:

#include "nrf_drv_rtc.h"
const nrf_drv_rtc_t rtc = NRF_DRV_RTC_INSTANCE(2);

static void rtc_handler(nrf_drv_rtc_int_type_t int_type)
{
    if (int_type == NRF_DRV_RTC_INT_COMPARE0)
    {
        sd_nvic_SystemReset();
    }
}

static void rtc_init()
{
    uint32_t err_code;

    nrf_drv_rtc_config_t rtc_config = NRF_DRV_RTC_DEFAULT_CONFIG;
    // Set counter frequency to 8, given by (32768/(PRESCALER+1)) 
    rtc_config.prescaler = 4095;

    //Initialize the RTC peripheral 
    err_code = nrf_drv_rtc_init(&rtc,&rtc_config, rtc_handler);
    if (err_code != NRF_SUCCESS)
    {
        NRF_LOG_INFO("Could not initalize RTC: \r\n");
    }
    
    //Set compare channel to trigger interrupt after COMPARE_COUNTERTIME seconds
    err_code = nrf_drv_rtc_cc_set(&rtc, 0, 120*8 , true);
    if (err_code != NRF_SUCCESS)
    {
        NRF_LOG_INFO("Could not initalize CC value: \r\n");
    }
    
    nrf_drv_rtc_enable(&rtc);   
}

After adding the code above you only have to call rtc_init() in nrf_dfu_init().

Resetting the counter is done writing directly by triggering the RTC2 Clear task, i.e. call the following snippet in nrf_dfu_req_handler_on_req() in nrf_dfu_req_handling.c

// Clear the counter variable
NRF_RTC2->TASKS_CLEAR = 1;

[WestCoastDaz]

Bjorn,

Thanks for your help, you solution is great! Would it be a good idea to disable the timer in the rtc_handler() before resetting? I don't want that timer running in the application code.

Thanks, Darren

[bjorn-spockeli]

Yes, that is a good suggestion, call nrf_drv_rtc_disable and then nrf_drv_rtc_uninit in the rtc_handler(). Not sure if you must call nrf_drv_rtc_disable before calling nrf_drv_rtc_uninit, but better safe than sorry.

[Jeff]

I also want to add a timeout in 12.2.0 secure bootloader. I see that all the app_timer files and init is already done in the default project. I just added app_timer_create() and app_timer_start() to timers_init() in nrf_dfu.c and call sd_nvic_SystemReset() when the timer expires. It seems to work. Is there a reason to go through all the trouble of using RTC?

[WestCoastDaz]

Jeff,

It may be due to the fact that it seems like Nordic isn't using the timers in the DFU bootloader. Maybe the are going to remove them in a feature version. Even though there is a call to APP_TIMER_APPSH_INIT I can find app_timer_create() or app_timer_start() used in the bootloader.

[bjorn-spockeli]

@jeff : It is possible to use the application timer to create a one-shot timer, but there is no app_timer API to reset the counter at a regular interval like the WDT does. You could clear the RTC1 counter by writing to the peripheral registers directly, but that might affect the application scheduler. Therefore, I opted to use one of the unused RTCs directly where you can clear the counter without worrying about interfering with the application scheduler.