Developing a custom bootloader

[Norbert]

Hello Nordic team,

I am faced with the problem of developing a custom bootloader which actively pulls FW from an external mass-storage. AFAIK, the SDK only supports OTA or UART where the nRF device is slave to a host device which pushes the FW.

What would you recommend as a best way to tackle the problem? Do I need to dissect the SDK to see how the different functions need to be implemented? Could the nrfx driver set be of any help here? Ideally you could point me to a sample implementation.

Thanks and with best regards,

Norbert

[Norbert]

P.S.: I came across the document Bootloader_External_Flash_Modifications.pdf (/cfs-file/__key/communityserver-discussions-components-files/4/Bootloader_5F00_External_5F00_Flash_5F00_Modifications.pdf) which was an attachment to a forum post. The document looks quite promising even though it is not clear to which SDK version it refers to.

[Marjeris Romero]

Hi,

I am sorry for the late reply. This document refers to nRF5 SDK. Have you come far with your custom bootloader?

Another idea is to replace the pstorage calls in the bootloader, i.e, instead of using pstorage to write it to internal flash you use a function that takes some parametrers but writes to external flash instead. See this thread for more information.

[Norbert]

Hi,

Marjeris Romero said:

I am sorry for the late reply.

No problem...

I am still fighting with the latest libraries to get access to the external memory so I have not yet touched the core of the bootloader. The nRF52 SDK is fine as I am using an nRF52840.

Marjeris Romero said:

Another idea is to replace the pstorage calls in the bootloade

This is not quite what I want to achieve. How the image arrives in the external memory does not concern the nRF. I just need to read the image in the bootloader and write it to the internal Flash.

[Marjeris Romero]

Hi Norbert,

Norbert said:

This is not quite what I want to achieve. How the image arrives in the external memory does not concern the nRF. I just need to read the image in the bootloader and write it to the internal Flash.

I see, if you only one to read from the external flash and write to the internal then it should be easier and you don't need to change pstorage. In your bootloader example you will need to add SPI or QSPI drivers to read the image from the external flash.

Something similar is done in the USB MSC example in nRF5 SDK, where the file system on QSPI memory is manupulated from the application. You can take a look at that: https://infocenter.nordicsemi.com/topic/sdk_nrf5_v17.1.0/usbd_msc_example.html

[Norbert]

Hi,

Just to give some final feedback and maybe clues to other people intending to do something similar. I got my bootloader apparently working, even though I do not have an application yet which is fit to run.

The document Bootloader_External_Flash_Modifications.pdf (/cfs-file/__key/communityserver-discussions-components-files/4/Bootloader_5F00_External_5F00_Flash_5F00_Modifications.pdf) is pure gold. A couple of points to watch out for:

• Choose a suitable format for the file containing the firmware you want to install. You need to have access to the init record while the bootloader is running. I modified the pc_nrfutil script to be able to write a stream of instructions to a file. This way, the bootloader has everything it needs, even to do the block CRC verification on-the-fly.
• You might want to install SD and APP at the same time if there is ever an incompatibility between the ones already installed and the new FW package. To handle multiple updates, I commented out the call to nrf_dfu_settings_write_and_backup() in nrf_dfu_req_handler.c and let that part execute after all updates have been performed.

[Marjeris Romero]

Thanks for your update!