Add top level docs explaining how to get access to rcc, afio, clocks and flash

Author: TheZoq2

src/lib.rs

@@ -44,6 +44,26 @@
 //! * C, D, E => `high` feature
 //! * F, G => `xl` feature
 //!
+//! ## Commonly used setup
+//! Almost all peripherals require references to some registers in `RCC` and `AFIO`. The following
+//! code shows how to set up those registers
+//!
+//! ```rust
+//! // Get access to the device specific peripherals from the peripheral access crate
+//! let dp = pac::Peripherals::take().unwrap();
+//!
+//! // Take ownership over the raw flash and rcc devices and convert them into the corresponding
+//! // HAL structs
+//! let mut flash = dp.FLASH.constrain();
+//! let mut rcc = dp.RCC.constrain();
+//!
+//! // Freeze the configuration of all the clocks in the system and store the frozen frequencies in
+//! // `clocks`
+//! let clocks = rcc.cfgr.freeze(&mut flash.acr);
+//!
+//! // Prepare the alternate function I/O registers
+//! let mut afio = dp.AFIO.constrain(&mut rcc.apb2);
+//! ```
 //!
 //! ## Usage examples
 //!

src/rcc.rs

@@ -203,6 +203,19 @@ impl CFGR {
         self
     }
 
+    /// Applies the clock configuration and returns a `Clocks` struct that signifies that the
+    /// clocks are frozen, and contains the frequencies used. After this function is called,
+    /// the clocks can not change
+    ///
+    /// Usage:
+    ///
+    /// ```rust
+    /// let dp = pac::Peripherals::take().unwrap();
+    /// let mut flash = dp.FLASH.constrain();
+    /// let mut rcc = dp.RCC.constrain();
+    /// let clocks = rcc.cfgr.freeze(&mut flash.acr);
+    /// ```
+
     pub fn freeze(self, acr: &mut ACR) -> Clocks {
         let pllsrcclk = self.hse.unwrap_or(HSI / 2);
 
@@ -456,6 +469,7 @@ impl BKP {
 /// ```rust
 /// let dp = pac::Peripherals::take().unwrap();
 /// let mut rcc = dp.RCC.constrain();
+/// let mut flash = dp.FLASH.constrain();
 ///
 /// let clocks = rcc.cfgr.freeze(&mut flash.acr);
 /// ```