diff --git a/src/rcc.rs b/src/rcc.rs
index 09ccb5c..78a16d5 100644
--- a/src/rcc.rs
+++ b/src/rcc.rs
@@ -1,2 +1,188 @@
+//! Reset and Clock Control
+//!
+
+use crate::stm32::RCC;
+use crate::time::Hertz;
+
+#[cfg(feature = "log")]
+use log::debug;
+
 mod core_clocks;
 mod reset_reason;
+
+pub use core_clocks::CoreClocks;
+pub use reset_reason::ResetReason;
+
+/// Configuration of the core clocks
+pub struct Config {
+    hse: Option<u32>,
+    bypass_hse: bool,
+    lse: Option<u32>,
+    sys_ck: Option<u32>,
+    per_ck: Option<u32>,
+    audio_ck: Option<u32>,
+    rcc_hclk: Option<u32>,
+    rcc_pclk1: Option<u32>,
+    rcc_pclk2: Option<u32>,
+    rcc_pclk3: Option<u32>,
+    #[cfg(feature = "rm0481")]
+    rcc_pclk4: Option<u32>,
+}
+
+/// Extension trait that constrains the `RCC` peripheral
+pub trait RccExt {
+    /// Constrains the `RCC` peripheral so it plays nicely with the
+    /// other abstractions
+    fn constrain(self) -> Rcc;
+}
+
+impl RccExt for RCC {
+    fn constrain(self) -> Rcc {
+        Rcc {
+            config: Config {
+                hse: None,
+                bypass_hse: false,
+                lse: None,
+                sys_ck: None,
+                per_ck: None,
+                audio_ck: None,
+                rcc_hclk: None,
+                rcc_pclk1: None,
+                rcc_pclk2: None,
+                rcc_pclk3: None,
+                #[cfg(feature = "rm0481")]
+                rcc_pclk4: None,
+            },
+            rb: self,
+        }
+    }
+}
+
+/// Constrained RCC peripheral
+///
+/// Generated by calling `constrain` on the PAC's RCC peripheral.
+///
+/// ```rust
+/// let dp = stm32::Peripherals::take().unwrap();
+/// let rcc = dp.RCC.constrain();
+/// ```
+pub struct Rcc {
+    config: Config,
+    pub(crate) rb: RCC,
+}
+
+impl Rcc {
+    /// Gets and clears the reason of why the mcu was reset
+    pub fn get_reset_reason(&mut self) -> ResetReason {
+        reset_reason::get_reset_reason(&mut self.rb)
+    }
+}
+
+/// Core Clock Distribution and Reset (CCDR)
+///
+/// Generated when the RCC is frozen. The configuration of the Sys_Ck `sys_ck`,
+/// AHB clocks `hclk`, APB clocks `pclkN` and PLL outputs `pllN_X_ck` are
+/// frozen. However the distribution of some clocks may still be modified and
+/// peripherals enabled / reset by passing this object to other implementations
+/// in this stack.
+pub struct Ccdr {
+    /// A record of the frozen core clock frequencies
+    pub clocks: CoreClocks,
+}
+
+const MAX_SYSCLK_FREQ_HZ: u32 = 250_000_000;
+
+/// Setter defintion for pclk 1 - 4
+macro_rules! pclk_setter {
+    ($($name:ident: $pclk:ident,)+) => {
+        $(
+            /// Set the peripheral clock frequency for APB
+            /// peripherals.
+            #[must_use]
+            pub fn $name(mut self, freq: Hertz) -> Self {
+                assert!(freq.raw() <= MAX_SYSCLK_FREQ_HZ,
+                    "Max frequency is {MAX_SYSCLK_FREQ_HZ}Hz");
+                self.config.$pclk = Some(freq.raw());
+                self
+            }
+        )+
+    };
+}
+
+impl Rcc {
+    /// Uses HSE (external oscillator) instead of HSI (internal RC
+    /// oscillator) as the clock source. Will result in a hang if an
+    /// external oscillator is not connected or it fails to start.
+    #[must_use]
+    pub fn use_hse(mut self, freq: Hertz) -> Self {
+        self.config.hse = Some(freq.raw());
+        self
+    }
+
+    /// Use an external clock signal rather than a crystal oscillator,
+    /// bypassing the XTAL driver.
+    #[must_use]
+    pub fn bypass_hse(mut self) -> Self {
+        self.config.bypass_hse = true;
+        self
+    }
+
+    /// Set SYSCLK frequency
+    #[must_use]
+    pub fn sys_ck(mut self, freq: Hertz) -> Self {
+        assert!(
+            freq.raw() <= MAX_SYSCLK_FREQ_HZ,
+            "Max frequency is {MAX_SYSCLK_FREQ_HZ}Hz"
+        );
+        self.config.sys_ck = Some(freq.raw());
+        self
+    }
+
+    /// Set SYSCLK frequency - ALIAS
+    #[must_use]
+    pub fn sysclk(self, freq: Hertz) -> Self {
+        self.sys_ck(freq)
+    }
+
+    /// Set peripheral clock frequency
+    #[must_use]
+    pub fn per_ck(mut self, freq: Hertz) -> Self {
+        self.config.per_ck = Some(freq.raw());
+        self
+    }
+
+    /// Set low speed external clock frequency
+    pub fn lse_ck(mut self, freq: Hertz) -> Self {
+        self.config.lse = Some(freq.raw());
+        self
+    }
+
+    /// Set external AUDIOCLK frequency
+    #[must_use]
+    pub fn audio_ck(mut self, freq: Hertz) -> Self {
+        self.config.audio_ck = Some(freq.raw());
+        self
+    }
+
+    /// Set the peripheral clock frequency for AHB peripherals.
+    #[must_use]
+    pub fn hclk(mut self, freq: Hertz) -> Self {
+        assert!(
+            freq.raw() <= MAX_SYSCLK_FREQ_HZ,
+            "Max frequency is {MAX_SYSCLK_FREQ_HZ}Hz"
+        );
+        self.config.rcc_hclk = Some(freq.raw());
+        self
+    }
+
+    pclk_setter! {
+        pclk1: rcc_pclk1,
+        pclk2: rcc_pclk2,
+        pclk3: rcc_pclk3,
+    }
+
+    #[cfg(feature = "rm0481")]
+    pclk_setter! {
+        pclk4: rcc_pclk4,
+    }
+}
diff --git a/src/rcc/core_clocks.rs b/src/rcc/core_clocks.rs
index e65036f..3992802 100644
--- a/src/rcc/core_clocks.rs
+++ b/src/rcc/core_clocks.rs
@@ -79,7 +79,6 @@ macro_rules! pll_getter {
     };
 }
 
-#[allow(dead_code)]
 impl CoreClocks {
     /// Returns the frequency of AHB1,2,3 busses
     pub fn hclk(&self) -> Hertz {
diff --git a/src/rcc/reset_reason.rs b/src/rcc/reset_reason.rs
index 1f31097..a05285b 100644
--- a/src/rcc/reset_reason.rs
+++ b/src/rcc/reset_reason.rs
@@ -5,7 +5,6 @@ use core::fmt::Display;
 
 /// Gets and clears the reason of why the mcu was reset
 #[rustfmt::skip]
-#[allow(dead_code)]
 pub fn get_reset_reason(rcc: &mut crate::stm32::RCC) -> ResetReason {
     let reset_reason = rcc.rsr().read();
 
@@ -55,7 +54,6 @@ pub fn get_reset_reason(rcc: &mut crate::stm32::RCC) -> ResetReason {
 
 /// Gives the reason why the mcu was reset
 #[derive(Debug, Copy, Clone)]
-#[allow(dead_code)]
 pub enum ResetReason {
     /// The mcu went from not having power to having power and resetting
     PowerOnReset,