nrf51 flashing

[gaalb]

Dear Bitcraze team!

I'd like to attach a u.FL antenna to my crazyflie 2.1. I've read here, that in order to make the crazyflie use this antenna instead of the chip antenna, I need to modify and re-compile the firmware of the nrf51 chip.
To this end, I cloned the latest version of the nrf51 firmware, and after installing the arm-none-eabi toolchain, I could compile the firmware like so:

aimotion-i9@aimotioni9-MS-7D25:~/Projects/crazyflie2-nrf-firmware$ make PLATFORM=cf2 BLE=0
Generating version.h
python3 tools/build/generateVersionHeader.py --crazyflie-base /home/aimotion-i9/Projects/crazyflie2-nrf-firmware --output _build/version.h
/home/aimotion-i9/Projects/crazyflie2-nrf-firmware
Compiling file: main.c
Linking target: _build/cf2_nrf.out

   text	   data	    bss	    dec	    hex	filename
  24844	    164	   4584	  29592	   7398	_build/cf2_nrf.out

Preparing: _build/cf2_nrf.hex
Preparing: _build/cf2_nrf.bin
BLE  Disabled
Built for platform cf2

I flashed this firmware to my crazyflie 2.1 via crazyradio, and it appears to go through fine:

aimotion-i9@aimotioni9-MS-7D25:~/Projects/crazyflie2-nrf-firmware$ make cload
Generating version.h
python3 tools/build/generateVersionHeader.py --crazyflie-base /home/aimotion-i9/Projects/crazyflie2-nrf-firmware --output _build/version.h
/home/aimotion-i9/Projects/crazyflie2-nrf-firmware
Compiling file: main.c
Linking target: _build/cf2_nrf.out

   text	   data	    bss	    dec	    hex	filename
  46012	    256	   6272	  52540	   cd3c	_build/cf2_nrf.out

Preparing: _build/cf2_nrf.bin
python3 -m cfloader flash _build/cf2_nrf.bin nrf51-fw
Restart the Crazyflie you want to bootload in the next
 10 seconds ...
Flashing 1 of 1 to nrf51 (fw): 46267 bytes (46 pages) .1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1

However, after the flashing is over, the drone's M2 blue light stays on, solid without blinking. The drone cannot be turned off via the on/off button, only via unplugging the battery. It cannot connect to my computer using a crazyradio, although I can put it into bootloader mode again by long pressing the on/off button. In order to make it usable again, I need to do a cold boot recovery. Regarding the solid blue light, I read here, that this may indicate corrupted nrf51 firmware, but I'm not sure where it could've got corrupted, as I haven't yet modified anything about the firmware, and used the latest version.
In addition, in order to root out the issue, I tried to build with the bluetooth enabled, and/or flash with the following command, but had the same result:

python3 -m cfloader flash cf2_nrf.bin nrf51-fw

Could you provide some pointers on achieving my goal of using an external u.FL antenna, and compiling/flashing firmware to the nrf51 over crazyradio?

Thanks a lot for your help!
Botond Gaál

[gemenerik]

Have you already attached the antenna, or is this happening with a completely stock Crazyflie—radio, antenna, and firmware (both STM and NRF) unchanged?

It looks like the firmware flashed fully. Does the drone restart normally, or does it go straight into the solid blue LED state? No red blinking bursts indicating an assert?

[gaalb]

This happens whether the antenna is attached or not. I first wanted to make sure I can compile and flash the stock firmware before making any modifications.
The drone does not restart after the flash (or at least I don't think it does, it surely doesn't spin each propeller to imitate a tune). It goes straight into the solid blue LED state, no red blinking.

[ToveRumar]

Hi @gaalb !

Im not sure I understand exactly what is happening.

Before flashing, do you have any modifications done to the FW on the Crazyflie? Its just normal stock FW from the latest release?

Do you think it would be possible for you to submit a short video of the process, from normally working to flashing to unresponsive?

[gaalb]

Hey @ToveRumar !
I will try to clarify what I'm attempting. I want to be able to flash custom firmware to the nrf51, because I'd like to make the crazyflie use an external u.FL antenna. However, before modifying the source code for the nrf51, I want to check whether I can actually compile and flash it. Starting out, I have a newly flashed, unmodified crazyflie 2.1 without the external antenna. I flashed its firmware from cfclient, which as far as I am aware flashes both the nrf51 and the stm32. From here, I followed the Building and Flashing instructions. This means that I:

• cloned the firmware from the github repo as it currently stands (2025.02.04)

• fetched the dependencies: ./tools/fetch-dependencies.sh

• compiled the firmware: make PLATFORM=cf2 BLE=0

• flashed it to the drone: make cload
  The flashing goes through, but from the flashing led state (indicating the process of flashing), the drone goes straight into a solid blue M2 led state. In this state:

• I cannot connect to the drone using cfclient

• I cannot turn the drone on or off using the power button

• I CAN put the drone into bootloader mode again, from where I can do a cold boot recovery to return to a responsive state

As requested, I will attach a video showing this process. It's too large to upload here, so here is a youtube link to it:
https://youtu.be/2ASxVsrh_NM

[ToveRumar]

Hi @gaalb !

Thank you so much for the detailed description and video!

This helped me very much when trying to find your issue!
It looks like your Crazyflie has an old NRF bootloader.

You can update the bootloader by flashing the latest release using cfclient (Connect->Bootloader->From Release)

Once this is done you should (if my hypothesis is correct) be able to flash the nrf software just like you showed in the video.

I hope this solves the issues you are facing!
I will make sure this is properly documented.

[gaalb]

Hey @ToveRumar !
I was flashing myfirmware from cfclient, but I wasn't using the latest release (I was using a release from 2023). This is because I had issues flashing firmware newer than 2024. I wrongly assumed this would not make a difference. The clue was in your picture: the ui of my cfclient was slightly different from yours; I was using an outdated cfclient. I updated my cfclient, and I can now flash the latest release (2024.10.12). Following this, I can now flash the nrf51 and the drone doesn't go unresponsive: I can connect to it in cfclient without issue.
That being said, while trying this, I stumbled upon a possibly related issue: After flashing the firmware compiled from source to the nrf51, and turning off the drone, it cannot be turned on by the power button, only by unplugging the battery and plugging it back in.
To clarify:

1. I flash the drone with the updated cfclient with the latest release (2024.10.12)
2. I compile the nrf51 firmware
3. I flash the nrf51 firmware, and this time it flashes correctly, I am able to connect to the drone in cfclient
4. I turn the drone off using the power button
5. The drone cannot be turned back on using the power button (it CAN be turned on by disconnecting the battery and then re-connecting it).

At first glance, this seems like a hardware issue, but I tried it with two different crazyflies, and both with the 250mAh and 350mAh batteries. I got the same result in all cases. This is not a major progress blocking issue like not being able to flash was, it's just an inconvenience. Shall I mark this thread resolved, or keep it open to investigate this (possibly related) issue?

[ToveRumar]

Hi @gaalb !

Great to hear this solved your issue! I have added a note in the NRF flashing guide about this as well.

Lets close this discussion and I can create and issue on the problem you are seeing.

Thank you again for the detailed description!