Changing REGOUT0 value to 3v3 in a DFU enabled software

[OnurGules]

Hello,

We have an NRF52840 based custom design board where the peripherals run on 3.3v. I based my code on a combination of ble_app_uart and ble_app_buttonless_dfu examples. It has been working great so far. However, recently we designed a new board where we want to use DCDC regulator both for the chip and the peripherals.

From what I can gather, what I need to do in my code is:

NRF_POWER->DCDCEN = 1;
NRF_POWER->DCDCEN0 = 1;

Also, to change the output voltage from REG0 regulator stage, I also need to write 0xFFFFFFFD to NRF_UICR->REGOUT0 register. I did some research on the forums and it seems that writing to UICR registers isn't trivial if you have a bootloader since uicr_bootloader_start_address, and uicr_mbr_params_page are also kept on UICR. So, I decided to modify the bootloader to change the UICR REGOUT0 register with a compile time constant. I listed the changes I made to the bootloader below:

-Added uicr_config.h and included it in main.c

-Defined REGOUT0 3v3 value as a constant like below:

const uint32_t REGOUT0 __attribute__((section(".uicr_regout0"))) = 0xFFFFFFFD;

-Modified flash_placement.xml:

  <MemorySegment name="UICR" start="0x10001000" size="0x308" fill="0xff">
      <ProgramSection alignment="4" keep="yes" load="no" name=".uicr_fill" fill="0xff" size="0x1" />
      <ProgramSection alignment="4" keep="Yes" load="Yes" name=".uicr_regout0" start="0x10001304" size="4"/>
  </MemorySegment>
  <MemorySegment name="uicr_bootloader_start_address" start="0x10001014" size="0x4">
    <ProgramSection alignment="4" keep="Yes" load="Yes" name=".uicr_bootloader_start_address" address_symbol="__start_uicr_bootloader_start_address" end_symbol="__stop_uicr_bootloader_start_address" start = "0x10001014" size="0x4" />
  </MemorySegment>
  <MemorySegment name="uicr_mbr_params_page" start="0x10001018" size="0x4">
    <ProgramSection alignment="4" keep="Yes" load="Yes" name=".uicr_mbr_params_page" address_symbol="__start_uicr_mbr_params_page" end_symbol="__stop_uicr_mbr_params_page" start = "0x10001018" size="0x4" />
  </MemorySegment>

-Modified Project Options->Linker->Memory Segments to

FLASH RX 0x0 0x100000;RAM1 RWX 0x20000000 0x40000;mbr_params_page RX 0x000FE000 0x1000;bootloader_settings_page RX 0x000FF000 0x1000;uicr_bootloader_start_address RX 0x10001014 0x4;uicr_mbr_params_page RX 0x10001018 0x4;UICR RWX 0x10001000 0x308

When I read the REGOUT0, uicr_bootloader_start_address, and uicr_mbr_params_page after flashing with:

nrfjprog --memrd 0x10001304 --w 32 --n 32
nrfjprog --memrd 0x10001014 --w 32 --n 32
nrfjprog --memrd 0x10001018 --w 32 --n 32

all three look correct, so I assume I'm not doing something wrong while writing them. However, if I flash this bootloader, my app, softdevice and a bootloader settings page using Segger Embedded Studio (bootloader, settings and the softdevice are correctly selected as additional load files in Project Options->Loader), the device gets stuck in bootloader as it starts advertising as DfuTarg. I generate the settings with this command:

nrfutil settings generate --family NRF52840 --application app.hex --application-version 0 --bootloader-version 0 --bl-settings-version 2 settings.hex

I am using SDK v17, hence the settings version 2. However, when run this command to read the bootloader settings in the flash with:

nrfjprog --readcode read.hex
nrfutil settings display read.hex

I'm getting this message:

Unknown Bootloader DFU settings version: 4294967295

Other than that, the settings look normal to me. Even if I perform a proper DFU with nRF Toolbox, the device doesn't boot my app and is stuck in bootloader. 

The question became much longer than I anticipated, but I wanted to share everything I did with you so that maybe you can spot my mistakes.

In summary, I would like to have these functionalities:

-Buttonless DFU

-DCDC REG0 output to be 3.3V

Can you please help?

Kind Regards,

Onur Gules.

[OnurGules]

Hi Vidar,

I tried setting it directly with nrfjprog as you described. The device works fine before setting REGOUT0 to 5, and is stuck in bootloader after.

I also found this thread:

https://devzone.nordicsemi.com/f/nordic-q-a/73814/regout0-set-to-3-3v-fail-buttonless-dfu

Not sure how, but their problem was related to their hardware. I have one more board so I'll see if I can make that one work.

Kind regards,

Onur.

[Vidar Berg]

Hi Onur,

Interesting, so it's likely not SW related then. I wonder if you may be running into the same problem as the forum user in the other post reported. Could try to lower the REG0 voltage to 3v0 or less to see if that works?

Kind regards,

Vidar

[OnurGules]

Hi Vidar,

I tried:

nrfjprog --memwr 0x10001304 --val 3
nrfjprog --reset

The device is stuck in bootloader mode after reset.

Kind regards,

Onur.

[Vidar Berg]

Hi Onur,

Have you had any progress on this? As I mentioned in the other post, the board should not really reset unless the supply voltage dips below 2.5v. Do you know if the supply voltage is stable in your case?

Kind regards,

Vidar

[OnurGules]

Hi Vidar,

We were able to find out the issue. I somehow missed that dfu_enter_check() was returning true because of this code:

    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;
    }

So, we were clearing NRF_BL_DFU_ENTER_METHOD_BUTTON_PIN while setting REGOUT 0 to 3V3. We don't actually have any buttons on our board so commenting out this code solved our problem.

Thanks for your help.

Onur Gules.