Merge pull request #3310 from Ecco/lptim

stm32: Add a first Lptim driver

10 files changed, 491 insertions, 9 deletions

diff --git a/embassy-stm32/Cargo.toml b/embassy-stm32/Cargo.toml
index 9a6a5908e..3c6484c96 100644
--- a/embassy-stm32/Cargo.toml
+++ b/embassy-stm32/Cargo.toml
@@ -72,7 +72,7 @@ rand_core = "0.6.3"
 sdio-host = "0.5.0"
 critical-section = "1.1"
 #stm32-metapac = { version = "15" }
-stm32-metapac = { git = "https://github.com/embassy-rs/stm32-data-generated", tag = "stm32-data-5ef354f3e49f790e47f5c818f243459742c9b83b" }
+stm32-metapac = { git = "https://github.com/embassy-rs/stm32-data-generated", tag = "stm32-data-ad00827345b4b758b2453082809d6e3b634b5364" }
 
 vcell = "0.1.3"
 nb = "1.0.0"
@@ -99,7 +99,7 @@ proc-macro2 = "1.0.36"
 quote = "1.0.15"
 
 #stm32-metapac = { version = "15", default-features = false, features = ["metadata"]}
-stm32-metapac = { git = "https://github.com/embassy-rs/stm32-data-generated", tag = "stm32-data-5ef354f3e49f790e47f5c818f243459742c9b83b", default-features = false, features = ["metadata"] }
+stm32-metapac = { git = "https://github.com/embassy-rs/stm32-data-generated", tag = "stm32-data-ad00827345b4b758b2453082809d6e3b634b5364", default-features = false, features = ["metadata"] }
 
 [features]
 default = ["rt"]
diff --git a/embassy-stm32/build.rs b/embassy-stm32/build.rs
index 1984a1420..19cf193d9 100644
--- a/embassy-stm32/build.rs
+++ b/embassy-stm32/build.rs
@@ -1015,6 +1015,9 @@ fn main() {
         (("hrtim", "CHE2"), quote!(crate::hrtim::ChannelEComplementaryPin)),
         (("hrtim", "CHF1"), quote!(crate::hrtim::ChannelFPin)),
         (("hrtim", "CHF2"), quote!(crate::hrtim::ChannelFComplementaryPin)),
+        (("lptim", "CH1"), quote!(crate::lptim::Channel1Pin)),
+        (("lptim", "CH2"), quote!(crate::lptim::Channel2Pin)),
+        (("lptim", "OUT"), quote!(crate::lptim::OutputPin)),
         (("sdmmc", "CK"), quote!(crate::sdmmc::CkPin)),
         (("sdmmc", "CMD"), quote!(crate::sdmmc::CmdPin)),
         (("sdmmc", "D0"), quote!(crate::sdmmc::D0Pin)),
diff --git a/embassy-stm32/src/adc/mod.rs b/embassy-stm32/src/adc/mod.rs
index 2ac0c0083..4ab82c1d9 100644
--- a/embassy-stm32/src/adc/mod.rs
+++ b/embassy-stm32/src/adc/mod.rs
@@ -4,7 +4,7 @@
 #![allow(missing_docs)] // TODO
 #![cfg_attr(adc_f3_v2, allow(unused))]
 
-#[cfg(not(adc_f3_v2))]
+#[cfg(not(any(adc_f3_v2, adc_u5)))]
 #[cfg_attr(adc_f1, path = "f1.rs")]
 #[cfg_attr(adc_f3, path = "f3.rs")]
 #[cfg_attr(adc_f3_v1_1, path = "f3_v1_1.rs")]
@@ -19,14 +19,16 @@ mod _version;
 use core::marker::PhantomData;
 
 #[allow(unused)]
-#[cfg(not(adc_f3_v2))]
+#[cfg(not(any(adc_f3_v2, adc_u5)))]
 pub use _version::*;
 #[cfg(any(adc_f1, adc_f3, adc_v1, adc_l0, adc_f3_v1_1))]
 use embassy_sync::waitqueue::AtomicWaker;
 
+#[cfg(not(any(adc_u5)))]
 pub use crate::pac::adc::vals;
-#[cfg(not(any(adc_f1, adc_f3_v2)))]
+#[cfg(not(any(adc_f1, adc_f3_v2, adc_u5)))]
 pub use crate::pac::adc::vals::Res as Resolution;
+#[cfg(not(any(adc_u5)))]
 pub use crate::pac::adc::vals::SampleTime;
 use crate::peripherals;
 
@@ -36,7 +38,7 @@ dma_trait!(RxDma, Instance);
 pub struct Adc<'d, T: Instance> {
     #[allow(unused)]
     adc: crate::PeripheralRef<'d, T>,
-    #[cfg(not(any(adc_f3_v2, adc_f3_v1_1)))]
+    #[cfg(not(any(adc_f3_v2, adc_f3_v1_1, adc_u5)))]
     sample_time: SampleTime,
 }
 
@@ -57,7 +59,7 @@ impl State {
 trait SealedInstance {
     #[allow(unused)]
     fn regs() -> crate::pac::adc::Adc;
-    #[cfg(not(any(adc_f1, adc_v1, adc_l0, adc_f3_v2, adc_f3_v1_1, adc_g0)))]
+    #[cfg(not(any(adc_f1, adc_v1, adc_l0, adc_f3_v2, adc_f3_v1_1, adc_g0, adc_u5)))]
     #[allow(unused)]
     fn common_regs() -> crate::pac::adccommon::AdcCommon;
     #[cfg(any(adc_f1, adc_f3, adc_v1, adc_l0, adc_f3_v1_1))]
@@ -163,7 +165,7 @@ foreach_adc!(
                 crate::pac::$inst
             }
 
-            #[cfg(not(any(adc_f1, adc_v1, adc_l0, adc_f3_v2, adc_f3_v1_1, adc_g0)))]
+            #[cfg(not(any(adc_f1, adc_v1, adc_l0, adc_f3_v2, adc_f3_v1_1, adc_g0, adc_u5)))]
             fn common_regs() -> crate::pac::adccommon::AdcCommon {
                 return crate::pac::$common_inst
             }
@@ -200,7 +202,7 @@ macro_rules! impl_adc_pin {
 /// Get the maximum reading value for this resolution.
 ///
 /// This is `2**n - 1`.
-#[cfg(not(any(adc_f1, adc_f3_v2)))]
+#[cfg(not(any(adc_f1, adc_f3_v2, adc_u5)))]
 pub const fn resolution_to_max_count(res: Resolution) -> u32 {
     match res {
         #[cfg(adc_v4)]
diff --git a/embassy-stm32/src/lib.rs b/embassy-stm32/src/lib.rs
index 98695e738..451f595e0 100644
--- a/embassy-stm32/src/lib.rs
+++ b/embassy-stm32/src/lib.rs
@@ -89,6 +89,8 @@ pub mod i2s;
 pub mod ipcc;
 #[cfg(feature = "low-power")]
 pub mod low_power;
+#[cfg(lptim)]
+pub mod lptim;
 #[cfg(ltdc)]
 pub mod ltdc;
 #[cfg(opamp)]
diff --git a/embassy-stm32/src/lptim/channel.rs b/embassy-stm32/src/lptim/channel.rs
new file mode 100644
index 000000000..17fc2fb86
--- /dev/null
+++ b/embassy-stm32/src/lptim/channel.rs
@@ -0,0 +1,18 @@
+/// Timer channel.
+#[derive(Clone, Copy)]
+pub enum Channel {
+    /// Channel 1.
+    Ch1,
+    /// Channel 2.
+    Ch2,
+}
+
+impl Channel {
+    /// Get the channel index (0..1)
+    pub fn index(&self) -> usize {
+        match self {
+            Channel::Ch1 => 0,
+            Channel::Ch2 => 1,
+        }
+    }
+}
diff --git a/embassy-stm32/src/lptim/mod.rs b/embassy-stm32/src/lptim/mod.rs
new file mode 100644
index 000000000..1649cc5b4
--- /dev/null
+++ b/embassy-stm32/src/lptim/mod.rs
@@ -0,0 +1,48 @@
+//! Low-power timer (LPTIM)
+
+pub mod pwm;
+pub mod timer;
+
+use crate::rcc::RccPeripheral;
+
+/// Timer channel.
+#[cfg(any(lptim_v2a, lptim_v2b))]
+mod channel;
+#[cfg(any(lptim_v2a, lptim_v2b))]
+pub use channel::Channel;
+
+pin_trait!(OutputPin, BasicInstance);
+pin_trait!(Channel1Pin, BasicInstance);
+pin_trait!(Channel2Pin, BasicInstance);
+
+pub(crate) trait SealedInstance: RccPeripheral {
+    fn regs() -> crate::pac::lptim::Lptim;
+}
+pub(crate) trait SealedBasicInstance: RccPeripheral {}
+
+/// LPTIM basic instance trait.
+#[allow(private_bounds)]
+pub trait BasicInstance: SealedBasicInstance + 'static {}
+
+/// LPTIM instance trait.
+#[allow(private_bounds)]
+pub trait Instance: BasicInstance + SealedInstance + 'static {}
+
+foreach_interrupt! {
+    ($inst:ident, lptim, LPTIM, GLOBAL, $irq:ident) => {
+        impl SealedInstance for crate::peripherals::$inst {
+            fn regs() -> crate::pac::lptim::Lptim {
+                crate::pac::$inst
+            }
+        }
+        impl SealedBasicInstance for crate::peripherals::$inst {
+        }
+        impl BasicInstance for crate::peripherals::$inst {}
+        impl Instance for crate::peripherals::$inst {}
+    };
+    ($inst:ident, lptim, LPTIM_BASIC, GLOBAL, $irq:ident) => {
+        impl SealedBasicInstance for crate::peripherals::$inst {
+        }
+        impl BasicInstance for crate::peripherals::$inst {}
+    };
+}
diff --git a/embassy-stm32/src/lptim/pwm.rs b/embassy-stm32/src/lptim/pwm.rs
new file mode 100644
index 000000000..1f43eb6ee
--- /dev/null
+++ b/embassy-stm32/src/lptim/pwm.rs
@@ -0,0 +1,168 @@
+//! PWM driver.
+
+use core::marker::PhantomData;
+
+use embassy_hal_internal::{into_ref, PeripheralRef};
+
+use super::timer::Timer;
+#[cfg(not(any(lptim_v2a, lptim_v2b)))]
+use super::OutputPin;
+#[cfg(any(lptim_v2a, lptim_v2b))]
+use super::{channel::Channel, timer::ChannelDirection, Channel1Pin, Channel2Pin};
+use super::{BasicInstance, Instance};
+use crate::gpio::{AfType, AnyPin, OutputType, Speed};
+use crate::time::Hertz;
+use crate::Peripheral;
+
+/// Output marker type.
+pub enum Output {}
+/// Channel 1 marker type.
+pub enum Ch1 {}
+/// Channel 2 marker type.
+pub enum Ch2 {}
+
+/// PWM pin wrapper.
+///
+/// This wraps a pin to make it usable with PWM.
+pub struct PwmPin<'d, T, C> {
+    _pin: PeripheralRef<'d, AnyPin>,
+    phantom: PhantomData<(T, C)>,
+}
+
+macro_rules! channel_impl {
+    ($new_chx:ident, $channel:ident, $pin_trait:ident) => {
+        impl<'d, T: BasicInstance> PwmPin<'d, T, $channel> {
+            #[doc = concat!("Create a new ", stringify!($channel), " PWM pin instance.")]
+            pub fn $new_chx(pin: impl Peripheral<P = impl $pin_trait<T>> + 'd) -> Self {
+                into_ref!(pin);
+                critical_section::with(|_| {
+                    pin.set_low();
+                    pin.set_as_af(
+                        pin.af_num(),
+                        AfType::output(OutputType::PushPull, Speed::VeryHigh),
+                    );
+                });
+                PwmPin {
+                    _pin: pin.map_into(),
+                    phantom: PhantomData,
+                }
+            }
+        }
+    };
+}
+
+#[cfg(not(any(lptim_v2a, lptim_v2b)))]
+channel_impl!(new, Output, OutputPin);
+#[cfg(any(lptim_v2a, lptim_v2b))]
+channel_impl!(new_ch1, Ch1, Channel1Pin);
+#[cfg(any(lptim_v2a, lptim_v2b))]
+channel_impl!(new_ch2, Ch2, Channel2Pin);
+
+/// PWM driver.
+pub struct Pwm<'d, T: Instance> {
+    inner: Timer<'d, T>,
+}
+
+#[cfg(not(any(lptim_v2a, lptim_v2b)))]
+impl<'d, T: Instance> Pwm<'d, T> {
+    /// Create a new PWM driver.
+    pub fn new(tim: impl Peripheral<P = T> + 'd, _output_pin: PwmPin<'d, T, Output>, freq: Hertz) -> Self {
+        Self::new_inner(tim, freq)
+    }
+
+    /// Set the duty.
+    ///
+    /// The value ranges from 0 for 0% duty, to [`get_max_duty`](Self::get_max_duty) for 100% duty, both included.
+    pub fn set_duty(&mut self, duty: u16) {
+        assert!(duty <= self.get_max_duty());
+        self.inner.set_compare_value(duty)
+    }
+
+    /// Get the duty.
+    ///
+    /// The value ranges from 0 for 0% duty, to [`get_max_duty`](Self::get_max_duty) for 100% duty, both included.
+    pub fn get_duty(&self) -> u16 {
+        self.inner.get_compare_value()
+    }
+
+    fn post_init(&mut self) {}
+}
+
+#[cfg(any(lptim_v2a, lptim_v2b))]
+impl<'d, T: Instance> Pwm<'d, T> {
+    /// Create a new PWM driver.
+    pub fn new(
+        tim: impl Peripheral<P = T> + 'd,
+        _ch1_pin: Option<PwmPin<'d, T, Ch1>>,
+        _ch2_pin: Option<PwmPin<'d, T, Ch2>>,
+        freq: Hertz,
+    ) -> Self {
+        Self::new_inner(tim, freq)
+    }
+
+    /// Enable the given channel.
+    pub fn enable(&mut self, channel: Channel) {
+        self.inner.enable_channel(channel, true);
+    }
+
+    /// Disable the given channel.
+    pub fn disable(&mut self, channel: Channel) {
+        self.inner.enable_channel(channel, false);
+    }
+
+    /// Check whether given channel is enabled
+    pub fn is_enabled(&self, channel: Channel) -> bool {
+        self.inner.get_channel_enable_state(channel)
+    }
+
+    /// Set the duty for a given channel.
+    ///
+    /// The value ranges from 0 for 0% duty, to [`get_max_duty`](Self::get_max_duty) for 100% duty, both included.
+    pub fn set_duty(&mut self, channel: Channel, duty: u16) {
+        assert!(duty <= self.get_max_duty());
+        self.inner.set_compare_value(channel, duty)
+    }
+
+    /// Get the duty for a given channel.
+    ///
+    /// The value ranges from 0 for 0% duty, to [`get_max_duty`](Self::get_max_duty) for 100% duty, both included.
+    pub fn get_duty(&self, channel: Channel) -> u16 {
+        self.inner.get_compare_value(channel)
+    }
+
+    fn post_init(&mut self) {
+        [Channel::Ch1, Channel::Ch2].iter().for_each(|&channel| {
+            self.inner.set_channel_direction(channel, ChannelDirection::OutputPwm);
+        });
+    }
+}
+
+impl<'d, T: Instance> Pwm<'d, T> {
+    fn new_inner(tim: impl Peripheral<P = T> + 'd, freq: Hertz) -> Self {
+        let mut this = Self { inner: Timer::new(tim) };
+
+        this.inner.enable();
+        this.set_frequency(freq);
+
+        this.post_init();
+
+        this.inner.continuous_mode_start();
+
+        this
+    }
+
+    /// Set PWM frequency.
+    ///
+    /// Note: when you call this, the max duty value changes, so you will have to
+    /// call `set_duty` on all channels with the duty calculated based on the new max duty.
+    pub fn set_frequency(&mut self, frequency: Hertz) {
+        self.inner.set_frequency(frequency);
+    }
+
+    /// Get max duty value.
+    ///
+    /// This value depends on the configured frequency and the timer's clock rate from RCC.
+    pub fn get_max_duty(&self) -> u16 {
+        self.inner.get_max_compare_value() + 1
+    }
+}
diff --git a/embassy-stm32/src/lptim/timer/channel_direction.rs b/embassy-stm32/src/lptim/timer/channel_direction.rs
new file mode 100644
index 000000000..a38df63cd
--- /dev/null
+++ b/embassy-stm32/src/lptim/timer/channel_direction.rs
@@ -0,0 +1,18 @@
+use crate::pac::lptim::vals;
+
+/// Direction of a low-power timer channel
+pub enum ChannelDirection {
+    /// Use channel as a PWM output
+    OutputPwm,
+    /// Use channel as an input capture
+    InputCapture,
+}
+
+impl From<ChannelDirection> for vals::Ccsel {
+    fn from(direction: ChannelDirection) -> Self {
+        match direction {
+            ChannelDirection::OutputPwm => vals::Ccsel::OUTPUTCOMPARE,
+            ChannelDirection::InputCapture => vals::Ccsel::INPUTCAPTURE,
+        }
+    }
+}
diff --git a/embassy-stm32/src/lptim/timer/mod.rs b/embassy-stm32/src/lptim/timer/mod.rs
new file mode 100644
index 000000000..e62fcab49
--- /dev/null
+++ b/embassy-stm32/src/lptim/timer/mod.rs
@@ -0,0 +1,133 @@
+//! Low-level timer driver.
+mod prescaler;
+
+use embassy_hal_internal::{into_ref, Peripheral, PeripheralRef};
+
+#[cfg(any(lptim_v2a, lptim_v2b))]
+use super::channel::Channel;
+#[cfg(any(lptim_v2a, lptim_v2b))]
+mod channel_direction;
+#[cfg(any(lptim_v2a, lptim_v2b))]
+pub use channel_direction::ChannelDirection;
+use prescaler::Prescaler;
+
+use super::Instance;
+use crate::rcc;
+use crate::time::Hertz;
+
+/// Low-level timer driver.
+pub struct Timer<'d, T: Instance> {
+    _tim: PeripheralRef<'d, T>,
+}
+
+impl<'d, T: Instance> Timer<'d, T> {
+    /// Create a new timer driver.
+    pub fn new(tim: impl Peripheral<P = T> + 'd) -> Self {
+        into_ref!(tim);
+
+        rcc::enable_and_reset::<T>();
+
+        Self { _tim: tim }
+    }
+
+    /// Enable the timer.
+    pub fn enable(&self) {
+        T::regs().cr().modify(|w| w.set_enable(true));
+    }
+
+    /// Disable the timer.
+    pub fn disable(&self) {
+        T::regs().cr().modify(|w| w.set_enable(false));
+    }
+
+    /// Start the timer in single pulse mode.
+    pub fn single_mode_start(&self) {
+        T::regs().cr().modify(|w| w.set_sngstrt(true));
+    }
+
+    /// Start the timer in continuous mode.
+    pub fn continuous_mode_start(&self) {
+        T::regs().cr().modify(|w| w.set_cntstrt(true));
+    }
+
+    /// Set the frequency of how many times per second the timer counts up to the max value or down to 0.
+    pub fn set_frequency(&self, frequency: Hertz) {
+        let f = frequency.0;
+        assert!(f > 0);
+
+        let pclk_f = T::frequency().0;
+
+        let pclk_ticks_per_timer_period = pclk_f / f;
+
+        let psc = Prescaler::from_ticks(pclk_ticks_per_timer_period);
+        let arr = psc.scale_down(pclk_ticks_per_timer_period);
+
+        T::regs().cfgr().modify(|r| r.set_presc((&psc).into()));
+        T::regs().arr().modify(|r| r.set_arr(arr.into()));
+    }
+
+    /// Get the timer frequency.
+    pub fn get_frequency(&self) -> Hertz {
+        let pclk_f = T::frequency();
+        let arr = T::regs().arr().read().arr();
+        let psc = Prescaler::from(T::regs().cfgr().read().presc());
+
+        pclk_f / psc.scale_up(arr)
+    }
+
+    /// Get the clock frequency of the timer (before prescaler is applied).
+    pub fn get_clock_frequency(&self) -> Hertz {
+        T::frequency()
+    }
+
+    /// Get max compare value. This depends on the timer frequency and the clock frequency from RCC.
+    pub fn get_max_compare_value(&self) -> u16 {
+        T::regs().arr().read().arr()
+    }
+}
+
+#[cfg(any(lptim_v2a, lptim_v2b))]
+impl<'d, T: Instance> Timer<'d, T> {
+    /// Enable/disable a channel.
+    pub fn enable_channel(&self, channel: Channel, enable: bool) {
+        T::regs().ccmr(0).modify(|w| {
+            w.set_cce(channel.index(), enable);
+        });
+    }
+
+    /// Get enable/disable state of a channel
+    pub fn get_channel_enable_state(&self, channel: Channel) -> bool {
+        T::regs().ccmr(0).read().cce(channel.index())
+    }
+
+    /// Set compare value for a channel.
+    pub fn set_compare_value(&self, channel: Channel, value: u16) {
+        T::regs().ccr(channel.index()).modify(|w| w.set_ccr(value));
+    }
+
+    /// Get compare value for a channel.
+    pub fn get_compare_value(&self, channel: Channel) -> u16 {
+        T::regs().ccr(channel.index()).read().ccr()
+    }
+
+    /// Set channel direction.
+    #[cfg(any(lptim_v2a, lptim_v2b))]
+    pub fn set_channel_direction(&self, channel: Channel, direction: ChannelDirection) {
+        T::regs()
+            .ccmr(0)
+            .modify(|w| w.set_ccsel(channel.index(), direction.into()));
+    }
+}
+
+#[cfg(not(any(lptim_v2a, lptim_v2b)))]
+impl<'d, T: Instance> Timer<'d, T> {
+    /// Set compare value for a channel.
+    pub fn set_compare_value(&self, value: u16) {
+        T::regs().cmp().modify(|w| w.set_cmp(value));
+    }
+
+    /// Get compare value for a channel.
+    pub fn get_compare_value(&self) -> u16 {
+        T::regs().cmp().read().cmp()
+    }
+}
diff --git a/embassy-stm32/src/lptim/timer/prescaler.rs b/embassy-stm32/src/lptim/timer/prescaler.rs
new file mode 100644
index 000000000..5d2326faf
--- /dev/null
+++ b/embassy-stm32/src/lptim/timer/prescaler.rs
@@ -0,0 +1,90 @@
+//! Low-level timer driver.
+
+use crate::pac::lptim::vals;
+
+pub enum Prescaler {
+    Div1,
+    Div2,
+    Div4,
+    Div8,
+    Div16,
+    Div32,
+    Div64,
+    Div128,
+}
+
+impl From<&Prescaler> for vals::Presc {
+    fn from(prescaler: &Prescaler) -> Self {
+        match prescaler {
+            Prescaler::Div1 => vals::Presc::DIV1,
+            Prescaler::Div2 => vals::Presc::DIV2,
+            Prescaler::Div4 => vals::Presc::DIV4,
+            Prescaler::Div8 => vals::Presc::DIV8,
+            Prescaler::Div16 => vals::Presc::DIV16,
+            Prescaler::Div32 => vals::Presc::DIV32,
+            Prescaler::Div64 => vals::Presc::DIV64,
+            Prescaler::Div128 => vals::Presc::DIV128,
+        }
+    }
+}
+
+impl From<vals::Presc> for Prescaler {
+    fn from(prescaler: vals::Presc) -> Self {
+        match prescaler {
+            vals::Presc::DIV1 => Prescaler::Div1,
+            vals::Presc::DIV2 => Prescaler::Div2,
+            vals::Presc::DIV4 => Prescaler::Div4,
+            vals::Presc::DIV8 => Prescaler::Div8,
+            vals::Presc::DIV16 => Prescaler::Div16,
+            vals::Presc::DIV32 => Prescaler::Div32,
+            vals::Presc::DIV64 => Prescaler::Div64,
+            vals::Presc::DIV128 => Prescaler::Div128,
+        }
+    }
+}
+
+impl From<&Prescaler> for u32 {
+    fn from(prescaler: &Prescaler) -> Self {
+        match prescaler {
+            Prescaler::Div1 => 1,
+            Prescaler::Div2 => 2,
+            Prescaler::Div4 => 4,
+            Prescaler::Div8 => 8,
+            Prescaler::Div16 => 16,
+            Prescaler::Div32 => 32,
+            Prescaler::Div64 => 64,
+            Prescaler::Div128 => 128,
+        }
+    }
+}
+
+impl From<u32> for Prescaler {
+    fn from(prescaler: u32) -> Self {
+        match prescaler {
+            1 => Prescaler::Div1,
+            2 => Prescaler::Div2,
+            4 => Prescaler::Div4,
+            8 => Prescaler::Div8,
+            16 => Prescaler::Div16,
+            32 => Prescaler::Div32,
+            64 => Prescaler::Div64,
+            128 => Prescaler::Div128,
+            _ => unreachable!(),
+        }
+    }
+}
+
+impl Prescaler {
+    pub fn from_ticks(ticks: u32) -> Self {
+        // We need to scale down to a 16-bit range
+        (ticks >> 16).next_power_of_two().into()
+    }
+
+    pub fn scale_down(&self, ticks: u32) -> u16 {
+        (ticks / u32::from(self)).try_into().unwrap()
+    }
+
+    pub fn scale_up(&self, ticks: u16) -> u32 {
+        u32::from(self) * ticks as u32
+    }
+}