How to disable APPROTECT permanently? DFU is needed

[TitanDaniel]

Hi,

I have been using nrf52840 chip for a while and now the new revision of the chip has APPROTECT feature that locks the writing until nrfjprog --recover is run and the whole chip is erased. This is my chip revision

I am using S340 (ANT_s340_nrf52840_6.1.1.hex)

I followed the instruction to disable APPROTECT using this code and called it in main function

void approtect_hw_disable(void)
{
    if ((NRF_UICR->APPROTECT & UICR_APPROTECT_PALL_Msk) 
       == (UICR_APPROTECT_PALL_Msk))
    {
        NRF_NVMC->CONFIG = NVMC_CONFIG_WEN_Wen << NVMC_CONFIG_WEN_Pos;
        while (NRF_NVMC->READY == NVMC_READY_READY_Busy) {}
        NRF_UICR->APPROTECT = (UICR_APPROTECT_PALL_HwDisabled << UICR_APPROTECT_PALL_Pos);
        while (NRF_NVMC->READY == NVMC_READY_READY_Busy) {}
        NRF_NVMC->CONFIG = NVMC_CONFIG_WEN_Ren << NVMC_CONFIG_WEN_Pos;
        while (NRF_NVMC->READY == NVMC_READY_READY_Busy) {}
        NVIC_SystemReset();
    }  
}

The chip is unlock but if I do a reset or power cycle, the chip will be locked again. 

I want to ask if there is a way to permanently disable APPROTECT feature,, which mean it will work as old revision chips.

Edit:

Problem solved! I must use the latest MDK (8.44.1) and recompile everything. I hope this will help others who looking for a solution!

Thank you so much!

[Hung Bui]

Hi Daniel, 
Thanks for letting us know. Please be aware that with the enchanced APPROTECT from revision 3 of the chip  you need to disable APPROTECT in both hardware and software. I would assume the older MDK doesn't have the software disable part enabled. 

Note that DFU and the bootloader is not affected by APPROTECT. APPROTECT only disconnects the chip from SWD interface (from the programmer) not the bootloader. 

[TitanDaniel]

Hi Hung,

I am now disable it with software only, can you please show me how to disable it on hardware?

Regards,

Daniel

[Hung Bui]

The code you provided in your question is actually disabling APPROTECT in the hardware. It's the code that written to UICR to disable APPROTECT. 
Please see here: https://infocenter.nordicsemi.com/topic/ps_nrf52840/dif.html?cp=5_0_0_3_7_1#concept_udr_mns_1s
In addition to hardware (write to UICR in flash, this only need to be done once) you need to disable it in firmware (write to  APPROTECT.DISABLE in the firmware, this need to be performed on every boot)