SDK12.2 Secure DFU Timeout

Question

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 · Accepted Answer

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: 
");
 }
 
 //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: 
");
 }
 
 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;

SDK12.2 Secure DFU Timeout

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