Flash protection nrf52840 SDK: 14.0.0

[VoidGreen]

I am trying to implement a bootloader with rewrite protection on nrf52840 with SDK: 14.0.0. But it seems that there is no flash write protection registers in nrf52840. So is there a way to implement a flash rewrite protection?

Thanks.

[Sigurd]

Hi,

The BPROT peripheral that is found in the nRF52832, has been replaced with the ACL peripheral on the nRF52840. ACL works similar to the BPROT(erase/write protection), but also adds support for protection against reading the flash.

You can find more information about the ACL here.

[Sigurd]

Are you testing this in an active debug session? I think the current implementation of ACL is that erase/write is allowed while debugging.

Here is the code I used to test this. LED3 will light if the data is successfully deleted, and re-written. If tested in non-debug mode session, the LED3 and LED4 will not light, indicating that the device hardfaults because there is an attempt to erase/write to protected flash.

#include <stdbool.h>
#include <stdint.h>

#include "boards.h"
#include "nordic_common.h"
#include "nrf.h"
#include "nrf_nvmc.h"

#define LED_PIN1 13 // Pin P0.13
#define LED_PIN2 14 // Pin P0.14
#define LED_PIN3 15 // Pin P0.15
#define LED_PIN4 16 // Pin P0.16

#define PAGE_SIZE 4096

#define REGION1_START 0xF0000  //0xF0000 
#define REGION1_SIZE PAGE_SIZE*10 //PAGE_SIZE*10





void led_off(uint8_t led)
{
    NRF_GPIO->OUTSET = (1UL << led);
}

void led_on(uint8_t led)
{
    NRF_GPIO->OUTCLR = (1UL << led);
}

void configure_leds(void)
{
    uint8_t led_pins[4] = {LED_PIN1, LED_PIN2, LED_PIN3, LED_PIN4};
    for (int i = 0; i < sizeof(led_pins); i++)
    {
        // setup led gpio in output mode
        led_off(led_pins[i]);
        NRF_GPIO->PIN_CNF[led_pins[i]] = (GPIO_PIN_CNF_SENSE_Disabled << GPIO_PIN_CNF_SENSE_Pos) | (GPIO_PIN_CNF_DRIVE_S0S1 << GPIO_PIN_CNF_DRIVE_Pos) | (GPIO_PIN_CNF_PULL_Disabled << GPIO_PIN_CNF_PULL_Pos) | (GPIO_PIN_CNF_INPUT_Disconnect << GPIO_PIN_CNF_INPUT_Pos) | (GPIO_PIN_CNF_DIR_Output << GPIO_PIN_CNF_DIR_Pos);
    }
}

int test_writeProtect(void)
{
    uint32_t errcode = 0;

    // Start by erasing region 1
    nrf_nvmc_page_erase(REGION1_START);

    //Writing to region 1
    nrf_nvmc_write_word(REGION1_START, 0xABBA1234);

    // Read before ACL region is configured
    uint32_t orig_data = 0;
    orig_data          = *((uint32_t *)REGION1_START);

    // Disable write/erase for region 1 with ACL
    NRF_ACL->ACL[0].ADDR = REGION1_START;
    NRF_ACL->ACL[0].SIZE = REGION1_SIZE;
    NRF_ACL->ACL[0].PERM = ACL_ACL_PERM_WRITE_Disable << ACL_ACL_PERM_WRITE_Pos;

    
    //Try to erase region 1
    nrf_nvmc_page_erase(REGION1_START);

    // Write to region 1
    nrf_nvmc_write_word(REGION1_START, 0xABBADEAD);

    // Try to read from region using CPU
    uint32_t new_data = 0;
    new_data          = *((uint32_t *)REGION1_START);

    if (new_data == 0xABBADEAD) // data successfully deleted, and re-written
    { 
        errcode = 1;
        led_on(LED_PIN3);
    }
    return errcode;
}

int main(void)
{
    configure_leds();
    led_on(LED_PIN1); // Start

    test_writeProtect();
    
    led_on(LED_PIN4);

    while (true)
    {
        // Do nothing.
    }
}
/** @} */