diff --git a/src/rcc.rs b/src/rcc.rs
index 53b67fa..09ccb5c 100644
--- a/src/rcc.rs
+++ b/src/rcc.rs
@@ -1 +1,2 @@
+mod core_clocks;
 mod reset_reason;
diff --git a/src/rcc/core_clocks.rs b/src/rcc/core_clocks.rs
new file mode 100644
index 0000000..e65036f
--- /dev/null
+++ b/src/rcc/core_clocks.rs
@@ -0,0 +1,146 @@
+//! Structure to represent frozen core clock frequencies
+
+use crate::time::Hertz;
+
+/// Frozen core clock frequencies
+///
+/// The existence of this value indicates that the core clock
+/// configuration can no longer be changed
+#[derive(Clone, Copy)]
+pub struct CoreClocks {
+    pub(super) hclk: Hertz,
+    pub(super) pclk1: Hertz,
+    pub(super) pclk2: Hertz,
+    pub(super) pclk3: Hertz,
+    pub(super) ppre1: u8,
+    pub(super) ppre2: u8,
+    pub(super) ppre3: u8,
+    pub(super) csi_ck: Option<Hertz>,
+    pub(super) hsi_ck: Option<Hertz>,
+    pub(super) hsi48_ck: Option<Hertz>,
+    pub(super) lsi_ck: Option<Hertz>,
+    pub(super) per_ck: Option<Hertz>,
+    pub(super) hse_ck: Option<Hertz>,
+    pub(super) lse_ck: Option<Hertz>,
+    pub(super) audio_ck: Option<Hertz>,
+    pub(super) mco1_ck: Option<Hertz>,
+    pub(super) mco2_ck: Option<Hertz>,
+    pub(super) pll1_p_ck: Option<Hertz>,
+    pub(super) pll1_q_ck: Option<Hertz>,
+    pub(super) pll1_r_ck: Option<Hertz>,
+    pub(super) pll2_p_ck: Option<Hertz>,
+    pub(super) pll2_q_ck: Option<Hertz>,
+    pub(super) pll2_r_ck: Option<Hertz>,
+    pub(super) timx_ker_ck: Hertz,
+    pub(super) timy_ker_ck: Hertz,
+    pub(super) sys_ck: Hertz,
+}
+
+/// Getters for pclk and ppre
+macro_rules! pclk_ppre_getter {
+    ($(($pclk:ident, $ppre:ident),)+) => {
+        $(
+            /// Returns the frequency of the APBn
+            pub fn $pclk(&self) -> Hertz {
+                self.$pclk
+            }
+            /// Returns the prescaler of the APBn
+            pub fn $ppre(&self) -> u8 {
+                self.$ppre
+            }
+        )+
+    };
+}
+
+/// Getters for optional clocks
+macro_rules! optional_ck_getter {
+    ($($opt_ck:ident: $doc:expr,)+) => {
+        $(
+            /// Returns `Some(frequency)` if
+            #[doc=$doc]
+            /// is running, otherwise `None`
+            pub fn $opt_ck(&self) -> Option<Hertz> {
+                self.$opt_ck
+            }
+        )+
+    };
+}
+
+/// Getters for pll clocks
+macro_rules! pll_getter {
+    ($($pll_ck:ident,)+) => {
+        $(
+            /// Returns `Some(frequency)` if the PLLx output is running,
+            /// otherwise `None`
+            pub fn $pll_ck(&self) -> Option<Hertz> {
+                self.$pll_ck
+            }
+        )+
+    };
+}
+
+#[allow(dead_code)]
+impl CoreClocks {
+    /// Returns the frequency of AHB1,2,3 busses
+    pub fn hclk(&self) -> Hertz {
+        self.hclk
+    }
+
+    pclk_ppre_getter! {
+        (pclk1, ppre1),
+        (pclk2, ppre2),
+        (pclk3, ppre3),
+    }
+
+    optional_ck_getter! {
+        csi_ck: "csi_ck",
+        hsi_ck: "hsi_ck",
+        hsi48_ck: "hsi48_ck",
+        per_ck: "per_ck",
+        hse_ck: "hse_ck",
+        lse_ck: "lse_ck",
+        lsi_ck: "lsi_ck",
+        audio_ck: "audio_ck",
+    }
+
+    /// Returns `Some(frequency)` if the MCO1 output is running, otherwise
+    /// `None`
+    pub fn mco1_ck(&self) -> Option<Hertz> {
+        self.mco1_ck
+    }
+
+    /// Returns `Some(frequency)` if the MCO2 output is running, otherwise
+    /// `None`
+    pub fn mco2_ck(&self) -> Option<Hertz> {
+        self.mco2_ck
+    }
+
+    pll_getter! {
+        pll1_p_ck,
+        pll1_q_ck,
+        pll1_r_ck,
+        pll2_p_ck,
+        pll2_q_ck,
+        pll2_r_ck,
+    }
+
+    /// Returns the input frequency to the SCGU
+    pub fn sys_ck(&self) -> Hertz {
+        self.sys_ck
+    }
+
+    /// Returns the input frequency to the SCGU - ALIAS
+    pub fn sysclk(&self) -> Hertz {
+        self.sys_ck
+    }
+
+    /// Returns the CK_INT frequency for timers on APB1
+    pub fn timx_ker_ck(&self) -> Hertz {
+        self.timx_ker_ck
+    }
+
+    /// Returns the CK_INT frequency for timers on APB2
+    pub fn timy_ker_ck(&self) -> Hertz {
+        self.timy_ker_ck
+    }
+}