# Introduction to the code
This page is meant to guide you through the source code, so you can find the relevant files for what you're working on.

## FreeRTOS
Infinitime is based on FreeRTOS, a real-time operating system. FreeRTOS provides several quality of life abstractions (for example easy software timers) and most importantly supports multiple tasks. You can sort of imagine them as processes or threads on a full operating system. The main "process" creates at least one task and then starts the FreeRTOS task scheduler. This main "process" is the standard main() function inside main.cpp . The task scheduler is responsible for giving every task enough cpu time. As there is only one core on the SoC of the PineTime, real concurrency is impossible and the scheduler has to swap tasks in and out to emulate it.

### Tasks
Tasks are created by calling `xTaskCreate` and passing a function with the signature `void functionName(void*)`. For more info on task creation see the [FreeRTOS Documentation](https://www.freertos.org/a00125.html).
In our case, main calls `systemTask.Start()`, which creates the **"MAIN" task**. The function running inside that task is `SystemTask::Work()`. Both functions are located inside systemtask/SystemTask.cpp . `SystemTask::Work()` initializes all the driver and controller objects. It also starts the **task "displayapp"**, which is responsible for launching and running apps, controlling the screen and handling touch events (or forwarding them to the active app). You can find the "displayapp" task inside displayapp/DisplayApp.cpp .
There are also other tasks that are responsible for Bluetooth ("ll" and "ble" inside libs/mynewt-nimble/porting/npl/freertos/src/nimble_port_freertos.c) and periodic tasks like heartrate measurements (heartratetask/HeartRateTask.cpp).

## Controllers
Controllers in InfiniTime are singleton objects that can provide access to certain resources to apps. Some of them interface with drivers, others are the driver for the resource. The resources provided don't have to be hardware-based. They are declared in main.cpp and initialized in systemtask/SystemTask.cpp . Some controllers can be passed by reference to apps that need access to the resource (for example vibration motor).
They reside in components inside their own subfolder.

## Apps
For more detail see the [Apps page](./Apps.md)

## Bluetooth
Header files with short documentation for the functions are inside libs/mynewt-nimble/nimble/host/include/host/ .