Jumping to bootloader without DFU

[CodeLoader]

Hello! We have an app with bootloader on SDK 15.3.0. Is there a way to jump from application into bootloader without setting byte 0 of GPREGRET register? I.e. without this: 

sd_power_gpregret_set(0, BOOTLOADER_DFU_SKIP_CRC)

The reason is: app has several ways to go into firmware update.
One is the standard Nordic DFU way, which triggers GPREGRET before resetting the device. The other way is receiving the firmware in the application.

If the firmware was received in the app, it replaces the old firmware in the modified bootloader before nrf_bootloader_init. So the application is valid, and it's the new firmware.
However it still gets stuck in the BLE DFU because of this check in nrf_bootloader.c, function dfu_enter_check():

if (NRF_BL_DFU_ENTER_METHOD_GPREGRET &&
(nrf_power_gpregret_get() & BOOTLOADER_DFU_START))
{
NRF_LOG_DEBUG("DFU mode requested via GPREGRET.");
return true;
}

We just need to enter the bootloader without triggering DFU advertising here. Maybe there's a way to jump directly to a bootloader address or something different?

[Vidar Berg]

Hello,

The bootloader will always run before the application after reset, so it is sufficient to just call NVIC_SystemReset() without setting the retention register first. The bootloader will only enter DFU mode if one of the "DFU_ENTER_METHOD" checks return true. 

[CodeLoader]

Why do I see different behavior if I set GPREGRET and don't set it before calling

nrf_pwr_mgmt_shutdown(NRF_PWR_MGMT_SHUTDOWN_GOTO_DFU)?

With  NVIC_SystemReset() it seems to enter the bootloader

[Vidar Berg]

nrf_pwr_mgmt_shutdown(NRF_PWR_MGMT_SHUTDOWN_GOTO_DFU) calls NVIC_SystemReset() at the end of its shutdown procedure.

CodeLoader said:

Why do I see different behavior if I set GPREGRET and don't set it before calling

It should be cleared before you call NVIC_SystemReset()/nrf_pwr_mgmt_shutdown() if you don't want the bootloader to enter DFU mode.

    /* Clear POWER->GPREGRET0 */
    err_code = sd_power_gpregret_clr(0, 0xffffffff);
    VERIFY_SUCCESS(err_code);