Programming the nRF52840 via UART

[Rakhsh]

Greetings.  I am on a mission to upgrade the BLE Firmware of nRF52840 via UART and ultimately via the UART communication between our main Micro (Microchip PIC) and nrf52840.  I reviewed the link at (https://github.com/jimmywong2003/nrf-slim-serial-uart-dfu-host-c-code) and have made the App to do what is intended via Windows 10.  It works as described if I do it using the Nordic’s DK board for nRf52840 (PCA10056 V0.9.0).  That is, I can program Softdevice (ver 6.1.1) and the SecureBootloader and then the App (ble_app_uart).  These are all under SDK 15.3.0.   However, if I were to do the same operation using Nordic DK connected to “our” hardware that has Fanstel BT840 (nrf52840), it doesn’t work!  I can program the SoftDevice and the App and that works fine.  However, if I program the Bootloader prior to programming the App, then it fails!  Any thoughts why it doesn’t work if I load the Bootloader prior to the App?

 Thank you.

[hmolesworth]

I don't think the BT840 has a 32kHz low-frequency crystal so maybe that's the issue; a firmware build is required which doesn't rely on that clock source, including an App which uses instead the low-spec RC oscillator instead of that crystal. Search the devzone for plenty of discussions on this topic, with details of workarounds for not using the crystal

[Rakhsh]

Thank you for your comment.  I don't think that's the issue.  As I said, if I program SoftDevice followed by the App, everything works. However, If I program Softdevice followed by "SecureBootloader" and then the App, it fails.  If the issue was the Crystal, then in the first case (Softdevice and App) would have failed too.  

[hmolesworth]

Perhaps try an explicit "erase all" first, if not already tried? Maybe the BT840 pre-programmed firmware has some awkward register settings in flash

[Rakhsh]

Yes, I had already done that in all cases.  I have done full erase and even sector erase, but same result.