- A cross-compiler : [ARM-GCC (10.3-2021.10)](https://developer.arm.com/downloads/-/gnu-rm)
- The NRF52 SDK 15.3.0 : [nRF-SDK v15.3.0](https://developer.nordicsemi.com/nRF5_SDK/nRF5_SDK_v15.x.x/nRF5_SDK_15.3.0_59ac345.zip)
- The Python 3 modules `cbor`, `intelhex`, `click` and `cryptography` modules for the `mcuboot` tool (see [requirements.txt](../tools/mcuboot/requirements.txt))
- To keep the system clean, you can install python modules into a python virtual environment (`venv`)
**BUILD_RESOURCES (\*\*)**| Generate external resource while building (needs [lv_font_conv](https://github.com/lvgl/lv_font_conv) and [python3-pil/pillow](https://pillow.readthedocs.io) module). |`-DBUILD_RESOURCES=1`
By default, this variable is set to *Release*. It compiles the code with size and speed optimizations. We use this value for all the binaries we publish when we [release](https://github.com/InfiniTimeOrg/InfiniTime/releases) new versions of InfiniTime.
The *Debug* mode disables all optimizations, which makes the code easier to debug. However, the binary size will likely be too big to fit in the internal flash memory. If you want to build and debug a *Debug* binary, you can disable some parts of the code that are not needed for the test you want to achieve. You can also apply the *Debug* mode selectively on parts of the application by applying the `DEBUG_FLAGS` only for the part (CMake target) you want to debug. For example, let's say you want to debug code related to LittleFS, simply set the compilation options for the RELEASE configuration of the target to `DEBUG_FLAGS` (in `src/CMakeLists.txt`). This will force the compilation of that target in *Debug* mode while the rest of the project will be built in *Release* mode. Example:
```
target_compile_options(littlefs PRIVATE
${COMMON_FLAGS}
$<$<CONFIG:DEBUG>: ${DEBUG_FLAGS}>
$<$<CONFIG:RELEASE>: ${DEBUG_FLAGS}> # Change from RELEASE_FLAGS to DEBUG_FLAGS
DFU files are the files you'll need to install your build of InfiniTime using OTA (over-the-air) mechanism. To generate the DFU file, the Python tool [adafruit-nrfutil](https://github.com/adafruit/Adafruit_nRF52_nrfutil) is needed on your system. Check that this tool is properly installed before enabling this option.
If you just want to build the project and run it on the Pinetime, using *pinetime-app* is recommended. See [this page](../bootloader/README.md) for more info about bootloader support.