RTIC applications are written in RTIC's Domain Specific Language (DSL). The DSL extends Rust syntax with custom attributes like `#[init]` and `#[idle]`.
RTIC makes a clearer distinction between the application's initialization phase, the `#[init]` function, and the application's main loop or main logic, the `#[idle]` function. The initialization phase runs with interrupts disabled and interrupts are re-enabled before the `idle` function is executed.
`rtic::app` is a procedural macro that generates extra Rust code, in addition to the user's functions. The fully expanded version of the macro can be found in the file `target/rtic-expansion.rs`. This file will contain the expansion of the procedural macro for the last compiled RTIC application.