Getting started with development

Programming the Crazyflie

In this tutorial we show the steps needed to change the software running in the Crazyflie, often called firmware. We will show how to modify the source code , how to build it and finally download and flash it to your Crazyflie. These are the necessary steps to write your own code and change the behaviour of your Crazyflie.

This tutorial is based on the virtual machine where all the tools you need are installed, configured and set up to make this really easy.

We assume that you have basic knowledge of the C-programming language.


For this tutorial you need:

  • A Crazyflie
  • A Crazyradio 2.0  or Crazyradio PA
  • A computer with the Virtual Machine (VM) installed.

For details on how to install the VM and Crazyradio see Getting started with the Crazyflie 2.X.

Note: Since the VM is an AMD64 install of Linux, it does not work on Apple-silicon Mac (M1/2/… processors). On an apple silicon mac you need to install the tools natively.

start the VM

Fire up the virtual machine to get started. It comes with all tools you need pre-installed and configured to make programming simple.

From this point on in the tutorial, all steps refer to actions in the virtual machine.

update source code

Double click the “update all projects” icon on the desktop. This pulls down the latest source code from GitHub for all projects.

Update all projects icon

Modify the source code

We will start out by modifying the source code. The update of the code is minimalistic, we will change the color of the front right LED from red to green.

start the editor

The pre-installed IDE (Integrated Development Environment) is Visual Studio Code. Double click the “Visual Studio Code” icon on the desktop to start it.

vscode icon

open the file

Use the File menu to select “Open Folder…” and navigate to the “projects” folder and then select the “crazyflie-firmware” folder and open it.

Project explorer

Navigate to or search (CTRL + p) for src/drivers/interface/led.h and click to open it.

change the code

Find the line

#define SYS_LED          LED_RED_R

and change it to

#define SYS_LED          LED_GREEN_R


Save the file through the File menu or by pressing CTRL + S

Build the source code

Now it’s time to build the source code into binary files that can be downloaded to the Crazyflie.

For more, and more detailed, information about developing the Crazyflie firmware you can go to the repository documentation here.

start the build

If there is no command line terminal at the bottom of the vscode window you can use the Terminal menu and select “New Terminal” to get access to a bash terminal window.

The build system for the Crazyflie firmware is based on make.

First navigate to the rootfolder of the crazyflie-firmware repository. Then you will need to create an default configuration file for the firmware:

$ make cf2_defconfig

If you want to build firmware for a different platform, please checkout the build instructions of the crazyflie-firmware.

Then you can start a build by issuing the following command in the terminal window in Visual Studio Code:

$ make

Or have the build go faster by using more cpu’s

$ make -j 12

To build the firmware. You should see something like the below on a successful build:

$ make
  CC    sensors_mpu9250_lps25h.o
  CC    sensors_bmi088_bmp388.o
  CC    main.o
  CC    nvic.o
  CC    led.o
  CC    usblink.o
  CC    ledseq.o
  CC    freeRTOSdebug.o
  CC    pm_stm32f4.o
  CC    radiolink.o
  CC    system.o
  CC    usddeck.o
  CC    cfassert.o
  VTMPL version.c
  CC    version.o
  LD    cf2.elf
  COPY  cf2.hex
  COPY  cf2.bin
  DFUse cf2.dfu
Build for the CF2 platform!
Build 11:0864ef92245a (2021.03 +11) MODIFIED
Version extracted from git
Crazyloader build!
Flash |  242184/1032192 (23%),  790008 free | text: 236372, data: 5812, ccmdata: 0
RAM   |   71128/131072  (54%),   59944 free | bss: 65316, data: 5812
CCM   |   58380/65536   (89%),    7156 free | ccmbss: 58380, ccmdata: 0

Flash the Crazyflie

Now we have the binary files and it is time to download them to the Crazyflie and save them in the flash memory, often called flashing. Our new modified version of the firmware will replace what ever version you currently have installed. If you want to go back to the official firmware just re-flash the Crazyflie with an official release.

prepare the Crazyflie

Turn your Crazyflie 2.X off.

Start it in bootloader mode by pressing and holding the power button for 3 seconds. Both blue LEDs will blink.


In the terminal window type:

$ make cload

Printouts in the “Console” window shows the progress and the LEDs on the Crazyflie flicker.

$ make cload
python3 -m cfloader  flash  cf2.bin stm32-fw
Restart the Crazyflie you want to bootload in the next
 10 seconds ...
Connected to bootloader on the Crazyflie (version=0x10)
Target info: nrf51 (0xFE)
Flash pages: 232 | Page size: 1024 | Buffer pages: 1 | Start page: 88
144 KBytes of flash available for firmware image.
Target info: stm32 (0xFF)
Flash pages: 1024 | Page size: 1024 | Buffer pages: 10 | Start page: 16
1008 KBytes of flash available for firmware image.
Flashing 1 of 1 to stm32 (fw): 242639 bytes (237 pages) ..........10..........10..........10..........10..........10..........10..........10..........10..........10..........10..........10..........10..........10..........10..........10..........10..........10..........10..........10..........10..........10..........10..........10.......7
Reset in firmware mode ...

That's it!

The Crazyfile should restart when the flashing is complete and the front right LED of your Crazyflie should now be green instead of the normal red.

Congratulations to your first Crazyflie hack!

Next steps

Debugging using GDB

For a guide on debugging the Crazyflie firmware using GDB, see the firmware documentation here.

Alternatives to the VM

In this tutorial we used the VM, mainly because it is the easiest way to get started. However there two other ways to compile the code; installing the toolchain on your machine or using the Toolbelt. All solutions have their pros and cons but it is probably worth looking into all options if you plan to do some serious development.