Bootloader Question

[mpotter1435]

Hello,

We have just developed a custom PCB with the nRF52840 as the main microcontroller.

It is my understanding that these chips when populated from our distributor (Digikey), they do not come with a bootloader on them.

This is probably a stupid question but if there is no bootloader on the chip, are we still able to put it into bootloader mode?

Thanks,

Mike Potter

[khelmutlord]

Hello Mike,

You are correct--since they are bare, unprogrammed chips they will not have a bootloader (MCUboot or the Adafruit .uf2 bootloader, for instance).

You could create your own build of the Adafruit .uf2 bootloader for your specific board or enable MCUboot in your project.

For Adafruit:

https://github.com/adafruit/Adafruit_nRF52_Bootloader

If you intend to update via UART, USB (using SMP), or BLE please check out lesson 8 of the intermediate course on DevAcademy.

https://academy.nordicsemi.com/courses/nrf-connect-sdk-intermediate/lessons/lesson-8-bootloaders-and-dfu-fota/topic/bootloader-basics/

To actually program your boards, you can use the onboard debugger on any Nordic devkit. For info on programming with a 52840-DK, for instance, check here:

https://docs.nordicsemi.com/bundle/ug_nrf52840_dk/page/UG/dk/hw_debug_out.html

Note: for security, I would steer you in the direction of MCUboot since you are able to cryptographically sign the images that are downloaded to your device.

Hope this helps,

Helmut Lord

[Mounty1095]

Hi Helmut,

What needs to be done to cause the chip to enter "bootloader" mode and have it appear as a USB drive on Windows PC since it is a bare chip? Pressing reset twice as per instructions from nrf52840-DK does not cause the device to appear as a USB drive.

Is it because the reset pin (P0.18) is not configured as reset pin by default on a bare chip?

Thanks

[khelmutlord]

The nRF52840 does not have any USB bootloader by default. A nice!nano for instance uses the Adafruit bootloader above. It should be flashed through SWD. 

Do you have the SWDIO and SWCLK pins connected?