diff --git a/rp2040-hal/Cargo.toml b/rp2040-hal/Cargo.toml
index 782adb1..b0c0238 100644
--- a/rp2040-hal/Cargo.toml
+++ b/rp2040-hal/Cargo.toml
@@ -14,3 +14,4 @@ cortex-m = "0.7.1"
 embedded-hal = "0.2.4"
 nb = "1.0.0"
 rp2040-pac = "0.1.1"
+embedded-time = "0.10.1"
diff --git a/rp2040-hal/src/lib.rs b/rp2040-hal/src/lib.rs
index e8d96e2..8fb2aba 100644
--- a/rp2040-hal/src/lib.rs
+++ b/rp2040-hal/src/lib.rs
@@ -10,6 +10,8 @@
 extern crate cortex_m;
 extern crate embedded_hal as hal;
 extern crate nb;
+extern crate embedded_time;
+
 pub extern crate rp2040_pac as pac;
 
 pub mod adc;
@@ -24,3 +26,4 @@ pub mod timer;
 pub mod uart;
 pub mod usb;
 pub mod watchdog;
+pub mod xosc;
diff --git a/rp2040-hal/src/xosc.rs b/rp2040-hal/src/xosc.rs
new file mode 100644
index 0000000..2f07acf
--- /dev/null
+++ b/rp2040-hal/src/xosc.rs
@@ -0,0 +1,192 @@
+//! Crystal Oscillator (XOSC)
+// See [Chapter 2 Section 16](https://datasheets.raspberrypi.org/rp2040/rp2040_datasheet.pdf) for more details
+
+use core::{
+    convert::Infallible,
+    ops::RangeInclusive
+};
+
+use embedded_time::{
+    fraction::Fraction,
+    fixed_point::FixedPoint,
+    rate::{
+        Hertz,
+        Megahertz,
+    },
+    duration::{
+        Seconds,
+        Milliseconds,
+        Duration
+    }
+};
+
+use nb::Error::WouldBlock;
+
+/// State of the Crystal Oscillator (typestate trait)
+pub trait State {}
+
+/// XOSC is disabled (typestate)
+pub struct Disabled;
+
+/// XOSC is initialized, ie we've given parameters (typestate)
+pub struct Initialized {
+    freq_hz: Hertz<u64>
+}
+
+/// Stable state (typestate)
+pub struct Stable{
+    freq_hz: Hertz<u64>
+}
+
+/// XOSC is disabling (typestate)
+pub struct Disabling;
+
+/// XOSC is in dormant mode (see Chapter 2, Section 16, §5)
+pub struct Dormant;
+
+impl State for Disabled {}
+impl State for Initialized {}
+impl State for Stable {}
+impl State for Disabling {}
+impl State for Dormant {}
+
+/// Possible errors when initializing the CrystalOscillator
+pub enum Error {
+    /// Frequency is out of the 1-15MHz range (see datasheet)
+    FrequencyOutOfRange,
+
+    /// Argument is bad : overflows, ...
+    BadArgument
+}
+
+/// A Crystal Oscillator.
+pub struct CrystalOscillator<S: State> {
+    device: rp2040_pac::XOSC,
+    state: S
+}
+
+impl<S: State> CrystalOscillator<S> {
+    /// Transitions the oscillator to another state.
+    fn transition<To: State>(self, state: To) -> CrystalOscillator<To> {
+        CrystalOscillator {
+            device: self.device,
+            state: state
+        }
+    }
+
+    /// Releases the underlying device.
+    pub fn free(self) -> rp2040_pac::XOSC {
+        self.device
+    }
+}
+
+impl CrystalOscillator<Disabled> {
+
+    /// Creates a new CrystalOscillator from the underlying device.
+    pub fn new(dev: rp2040_pac::XOSC) -> Self {
+        CrystalOscillator {
+            device: dev,
+            state: Disabled
+        }
+    }
+
+    /// Initializes the XOSC : frequency range is set, startup delay is calculated and set.
+    pub fn initialize(self, frequency: Megahertz<u32>) -> Result<CrystalOscillator<Initialized>, Error> {
+
+        const ALLOWED_FREQUENCY_RANGE: RangeInclusive<Megahertz<u32>> = Megahertz(1)..=Megahertz(15);
+        const STABLE_DELAY: Milliseconds<u64> = Milliseconds(1_u64);
+        const DIVIDER: Fraction = Fraction::new(1, 256);
+
+        if !ALLOWED_FREQUENCY_RANGE.contains(&frequency) {
+            return Err(Error::FrequencyOutOfRange)
+        }
+
+        self.device.ctrl.write(|w| {
+            w.freq_range()._1_15mhz();
+            w
+        });
+
+        let freq_hz: Hertz<u64> = frequency.into();
+        let delay_sec: Seconds<u64> = STABLE_DELAY.into();
+
+        //let startup_delay = ((freq_hz / 1000) + 128) / 256;
+        let startup_delay = delay_sec.
+            checked_mul(freq_hz.integer()).and_then(|r|
+                 r.to_generic::<u64>(DIVIDER).ok()
+             ).
+            ok_or(Error::BadArgument)?;
+
+        self.device.startup.write(|w| unsafe {
+            w.delay().bits(*startup_delay.integer() as u16);
+            w
+        });
+
+        self.device.ctrl.write(|w| {
+            w.enable().enable();
+            w
+        });
+
+        Ok(self.transition(Initialized {
+            freq_hz: freq_hz
+        }))
+    }
+}
+
+/// A token that's given when the oscillator is stablilzed, and can be exchanged to proceed to the next stage.
+pub struct StableOscillatorToken {
+    _private : ()
+}
+
+impl CrystalOscillator<Initialized> {
+
+    /// One has to wait for the startup delay before using the oscillator, ie awaiting stablilzation of the XOSC
+    pub fn await_stabilization(&self) -> nb::Result<StableOscillatorToken, Infallible> {
+
+        if self.device.status.read().stable().bit_is_clear() {
+            return Err(WouldBlock)
+        }
+
+        Ok(StableOscillatorToken {
+            _private: ()
+        })
+    }
+
+    /// Returns the stablilzed oscillator
+    pub fn get_stable(self, _token: StableOscillatorToken) -> CrystalOscillator<Stable> {
+        let freq_hz = self.state.freq_hz;
+        self.transition(Stable {
+            freq_hz:freq_hz
+        })
+    }
+}
+
+impl CrystalOscillator<Stable> {
+
+    /// Operating frequency of the XOSC in hertz
+    pub fn operating_frequency(&self) -> Hertz<u64> {
+        self.state.freq_hz
+    }
+
+    /// Disables the XOSC
+    pub fn disable(self) -> CrystalOscillator<Disabling> {
+        self.device.ctrl.modify(|_r,w| {
+            w.enable().disable();
+            w
+        });
+
+        self.transition(Disabling)
+    }
+
+    /// Put the XOSC in dormant state
+    pub fn dormant(self) -> CrystalOscillator<Dormant> {
+        //taken from the C SDK
+        const XOSC_DORMANT_VALUE: u32 = 0x636f6d61;
+
+        self.device.dormant.write(|w| unsafe {
+            w.bits(XOSC_DORMANT_VALUE);
+            w
+        });
+
+        self.transition(Dormant)
+    }
+}