nRF52840, How to do buttonless DFU with nrf_power_gpregret_set?

[cpeng]

Hi Devzone:

Where can I find full document on how to use nrf_power_gpregret_set? 

Background: I am planing to do buttonless DFU without BLE but through usb cdc acm.

After digging around devzone I found a post suggesting putting this 2 lines of code into my application in order to enter DFU mode:

nrf_power_gpregret_set(0xB1);

NVIC_SystemReset();

The problem is there's not much info about what that value 0xB1 means.

Here is a screen shot of a document mentioning gpregre_set function:

No explanation on what value to set can be found on this page. Where can I get more info on this?

Thanks!

[bjorn-spockeli]

Hi Cpeng, 

the 0xB1 value is just a "magic number" that is written to the GPREGRET register, which is then checked by the bootloader. The BOOTLOADER_DFU_START number, i.e. 0xB1 is defined in nrf_bootloader_info.h

// from nrf_bootloader_info.h

#define BOOTLOADER_DFU_GPREGRET                 (0xB0)      /**< Magic pattern written to GPREGRET register to signal between main app and DFU. The 3 lower bits are assumed to be used for signalling purposes.*/
#define BOOTLOADER_DFU_START_BIT_MASK           (0x01)      /**< Bit mask to signal from main application to enter DFU mode using a buttonless service. */


#define BOOTLOADER_DFU_START    (BOOTLOADER_DFU_GPREGRET | BOOTLOADER_DFU_START_BIT_MASK)      /**< Magic number to signal that bootloader should enter DFU mode because of signal from Buttonless DFU in main app.*/

It is used when the application wants to enter the bootloader

uint32_t ble_dfu_buttonless_bootloader_start_finalize(void)
{
    uint32_t err_code;

    NRF_LOG_DEBUG("In ble_dfu_buttonless_bootloader_start_finalize\r\n");

    err_code = sd_power_gpregret_clr(0, 0xffffffff);
    VERIFY_SUCCESS(err_code);

    err_code = sd_power_gpregret_set(0, BOOTLOADER_DFU_START);
    VERIFY_SUCCESS(err_code);

    // Indicate that the Secure DFU bootloader will be entered
    m_dfu.evt_handler(BLE_DFU_EVT_BOOTLOADER_ENTER);

    // Signal that DFU mode is to be enter to the power management module
    nrf_pwr_mgmt_shutdown(NRF_PWR_MGMT_SHUTDOWN_GOTO_DFU);

    return NRF_SUCCESS;
}

A nRF52xxx device with a bootloader will always start the bootloader upon a reset. The bootloader will then call the function dfu_enter_check() to check if the nRF52xxx should stay in DFU mode or start the application in nrf_bootloader_init().

static bool dfu_enter_check(void)
{
    if (!app_is_valid(crc_on_valid_app_required()))
    {
        NRF_LOG_DEBUG("DFU mode because app is not valid.");
        return true;
    }

    if (NRF_BL_DFU_ENTER_METHOD_BUTTON &&
       (nrf_gpio_pin_read(NRF_BL_DFU_ENTER_METHOD_BUTTON_PIN) == 0))
    {
        NRF_LOG_DEBUG("DFU mode requested via button.");
        return true;
    }

    if (NRF_BL_DFU_ENTER_METHOD_PINRESET &&
       (NRF_POWER->RESETREAS & POWER_RESETREAS_RESETPIN_Msk))
    {
        NRF_LOG_DEBUG("DFU mode requested via pin-reset.");
        return true;
    }

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

    if (NRF_BL_DFU_ENTER_METHOD_BUTTONLESS &&
       (s_dfu_settings.enter_buttonless_dfu == 1))
    {
        NRF_LOG_DEBUG("DFU mode requested via bootloader settings.");
        return true;
    }

    return false;
}

ret_code_t nrf_bootloader_init(nrf_dfu_observer_t observer)
{
    NRF_LOG_DEBUG("In nrf_bootloader_init");

    ret_code_t                            ret_val;
    nrf_bootloader_fw_activation_result_t activation_result;
    uint32_t                              initial_timeout;
    bool                                  dfu_enter = false;

    m_user_observer = observer;

    if (NRF_BL_DFU_ENTER_METHOD_BUTTON)
    {
        dfu_enter_button_init();
    }

    ret_val = nrf_dfu_settings_init(false);
    if (ret_val != NRF_SUCCESS)
    {
        return NRF_ERROR_INTERNAL;
    }

    #if NRF_BL_DFU_ALLOW_UPDATE_FROM_APP
    // Postvalidate if DFU has signaled that update is ready.
    if (s_dfu_settings.bank_current == NRF_DFU_CURRENT_BANK_1)
    {
        postvalidate();
    }
    #endif

    // Check if an update needs to be activated and activate it.
    activation_result = nrf_bootloader_fw_activate();

    switch (activation_result)
    {
        case ACTIVATION_NONE:
            initial_timeout = NRF_BOOTLOADER_MS_TO_TICKS(NRF_BL_DFU_INACTIVITY_TIMEOUT_MS);
            dfu_enter       = dfu_enter_check();
            break;

        case ACTIVATION_SUCCESS_EXPECT_ADDITIONAL_UPDATE:
            initial_timeout = NRF_BOOTLOADER_MS_TO_TICKS(NRF_BL_DFU_CONTINUATION_TIMEOUT_MS);
            dfu_enter       = true;
            break;

        case ACTIVATION_SUCCESS:
            bootloader_reset(true);
            NRF_LOG_ERROR("Unreachable");
            return NRF_ERROR_INTERNAL; // Should not reach this.

        case ACTIVATION_ERROR:
        default:
            return NRF_ERROR_INTERNAL;
    }

    if (dfu_enter)
    {
        nrf_bootloader_wdt_init();
        scheduler_init();
        dfu_enter_flags_clear();

        // Call user-defined init function if implemented
        ret_val = nrf_dfu_init_user();
        if (ret_val != NRF_SUCCESS)
        {
            return NRF_ERROR_INTERNAL;
        }

        nrf_bootloader_dfu_inactivity_timer_restart(initial_timeout, inactivity_timeout);

        ret_val = nrf_dfu_init(dfu_observer);
        if (ret_val != NRF_SUCCESS)
        {
            return NRF_ERROR_INTERNAL;
        }

        NRF_LOG_DEBUG("Enter main loop");
        loop_forever(); // This function will never return.
        NRF_LOG_ERROR("Unreachable");
    }
    else
    {
        // Erase additional data like peer data or advertisement name
        ret_val = nrf_dfu_settings_additional_erase();
        if (ret_val != NRF_SUCCESS)
        {
            return NRF_ERROR_INTERNAL;
        }

        m_flash_write_done = false;
        nrf_dfu_settings_backup(flash_write_callback);
        ASSERT(m_flash_write_done);

        nrf_bootloader_app_start();
        NRF_LOG_ERROR("Unreachable");
    }

    // Should not be reached.
    return NRF_ERROR_INTERNAL;
}

Best regards

Bjørn

[cpeng]

Thanks for the detailed explanation sir!

So writing 0xB1 will make device enter DFU after reboot. But what values to write to cancel DFU?

[bjorn-spockeli]

Hi cpeng, 

the nRF52xxx will enter the bootloader if GPREGRET is set to 0xB1 and the device is reset. No action will be taken before a reset is performed. So if you do not want to enter DFU mode, then just clear the GPREGRET register before you reset, i.e. 

err_code = sd_power_gpregret_clr(0, 0xffffffff);

[cpeng]

Thanks. What's the diffrence between 

nrf_power_gpregret_set

and

sd_power_gpregret_set

?