Enabling access port protection from code

[Luk3]

Hello,

How reset device from code to take effect of enabling access port protection? NVIC_SystemReset() doesn't work. I can read flash using j-link.

Device: nRF52832

[Edvin]

Hello,

How do you enable the readback protection?

The two following ways seems to work:

You can set it as a const in e.g. your main.c file, outside any function:

const uint32_t approtect_set __attribute__((used,at(0x10001208))) = 0xFFFFFF00;

This will set the readback protection, and you don't need a system reset.

Otherwise, you can set it in the application, e.g. in the top of your main() function. This, however, requires a system reset, which you can do in application. Please use the delay, to prevent a system reset loop (which makes it difficult to reset the chip).

void nrf_nvmc_write_word(uint32_t address, uint32_t value)
{
    // Enable write.
    NRF_NVMC->CONFIG = NVMC_CONFIG_WEN_Wen;
    __ISB();
    __DSB();

    *(uint32_t*)address = value;
    while (NRF_NVMC->READY == NVMC_READY_READY_Busy) {;}

    NRF_NVMC->CONFIG = NVMC_CONFIG_WEN_Ren;
    __ISB();
    __DSB();
}

int main(void)
{
    nrf_delay_ms(1000);
    if (NRF_UICR->APPROTECT == 0xFFFFFFFF)
    {
        nrf_nvmc_write_word((uint32_t)&(NRF_UICR->APPROTECT), 0xFFFFFF00);
        
        NVIC_SystemReset();
    }    
    nrf_gpio_cfg_output(LED_1);
    nrf_gpio_cfg_output(LED_2);
    while (true)
    {
        if (NRF_UICR->APPROTECT != 0xFFFFFFFF)
            nrf_gpio_pin_toggle(LED_1);
        else
            nrf_gpio_pin_toggle(LED_2);
        nrf_delay_ms(100);
    }
}

You can of course remove the lines controlling the LEDs, but if you use a DK, it will show you that the registers are set correct.

Also, using nrfjprog to try to read the memory will give the return:

>nrfjprog --memrd 0x10001208

ERROR: The operation attempted is unavailable due to readback protection in

ERROR: your device. Please use --recover to unlock the device.

Best regards,

Edvin

[Luk3]

Hello,

I will try to add delay at begin. But why is it necessary? Why system can go into reset loop? Isn't APPROTECT register updated before program execution?

My code:

	if ((NRF_UICR->APPROTECT & UICR_APPROTECT_PALL_Msk) != UICR_APPROTECT_PALL_Enabled)
	{
		uint32_t tmp;

		/* Enable access to write to flash */
		NRF_NVMC->CONFIG = NVMC_CONFIG_WEN_Wen;
	    while (NRF_NVMC->READY == NVMC_READY_READY_Busy);

		/* Enable Access Port Protection
		 * Access to CPU registers and memory will be disabled
		 * to disable protection ERASEALL command must be applied. */
		tmp = NRF_UICR->APPROTECT & ~UICR_APPROTECT_PALL_Msk;
		NRF_UICR->APPROTECT = tmp | UICR_APPROTECT_PALL_Enabled;

	    while (NRF_NVMC->READY == NVMC_READY_READY_Busy);

		/* Perform reset to take effect of changes */
		NVIC_SystemReset();
	}

Console:

>nrfjprog --recover
Recovering device. This operation might take 30s.
Erasing user code and UICR flash areas.

>nrfjprog --program "file.hex"
Parsing hex file.
Reading flash area to program to guarantee it is erased.
Checking that the area to write is not protected.
Programing device.

>nrfjprog --memrd 0x10001208
0x10001208: FFFFFFFF                              |....|

>nrfjprog --run
Run.

>nrfjprog --memrd 0x10001208
0x10001208: FFFFFFFF                              |....|

>nrfjprog --reset
Applying system reset.
Run.

>nrfjprog --memrd 0x10001208
ERROR: The operation attempted is unavailable due to readback protection in
ERROR: your device. Please use --recover to unlock the device.

Best regards,
Lukasz

[Edvin]

Sorry. I forgot to include the nrf_nvmc_write_word() function. I updated my previous reply. Please try to use the nrf_nvmc_write_word() function that is included now.

BR,

Edvin