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diff --git a/embassy-mcxa/src/clocks/periph_helpers.rs b/embassy-mcxa/src/clocks/periph_helpers.rs
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+//! Peripheral Helpers
+//!
+//! The purpose of this module is to define the per-peripheral special handling
+//! required from a clocking perspective. Different peripherals have different
+//! selectable source clocks, and some peripherals have additional pre-dividers
+//! that can be used.
+//!
+//! See the docs of [`SPConfHelper`] for more details.
+
+use super::{ClockError, Clocks, PoweredClock};
+use crate::pac;
+
+/// Sealed Peripheral Configuration Helper
+///
+/// NOTE: the name "sealed" doesn't *totally* make sense because its not sealed yet in the
+/// embassy-mcxa project, but it derives from embassy-imxrt where it is. We should
+/// fix the name, or actually do the sealing of peripherals.
+///
+/// This trait serves to act as a per-peripheral customization for clocking behavior.
+///
+/// This trait should be implemented on a configuration type for a given peripheral, and
+/// provide the methods that will be called by the higher level operations like
+/// `embassy_mcxa::clocks::enable_and_reset()`.
+pub trait SPConfHelper {
+    /// This method is called AFTER a given MRCC peripheral has been enabled (e.g. un-gated),
+    /// but BEFORE the peripheral reset line is reset.
+    ///
+    /// This function should check that any relevant upstream clocks are enabled, are in a
+    /// reasonable power state, and that the requested configuration can be made. If any of
+    /// these checks fail, an `Err(ClockError)` should be returned, likely `ClockError::BadConfig`.
+    ///
+    /// This function SHOULD NOT make any changes to the system clock configuration, even
+    /// unsafely, as this should remain static for the duration of the program.
+    ///
+    /// This function WILL be called in a critical section, care should be taken not to delay
+    /// for an unreasonable amount of time.
+    ///
+    /// On success, this function MUST return an `Ok(freq)`, where `freq` is the frequency
+    /// fed into the peripheral, taking into account the selected source clock, as well as
+    /// any pre-divisors.
+    fn post_enable_config(&self, clocks: &Clocks) -> Result<u32, ClockError>;
+}
+
+/// Copy and paste macro that:
+///
+/// * Sets the clocksel mux to `$selvar`
+/// * Resets and halts the div, and applies the calculated div4 bits
+/// * Releases reset + halt
+/// * Waits for the div to stabilize
+/// * Returns `Ok($freq / $conf.div.into_divisor())`
+///
+/// Assumes:
+///
+/// * self is a configuration struct that has a field called `div`, which
+///   is a `Div4`
+///
+/// usage:
+///
+/// ```rust
+/// apply_div4!(self, clksel, clkdiv, variant, freq)
+/// ```
+///
+/// In the future if we make all the clksel+clkdiv pairs into commonly derivedFrom
+/// registers, or if we put some kind of simple trait around those regs, we could
+/// do this with something other than a macro, but for now, this is harm-reduction
+/// to avoid incorrect copy + paste
+macro_rules! apply_div4 {
+    ($conf:ident, $selreg:ident, $divreg:ident, $selvar:ident, $freq:ident) => {{
+        // set clksel
+        $selreg.modify(|_r, w| w.mux().variant($selvar));
+
+        // Set up clkdiv
+        $divreg.modify(|_r, w| {
+            unsafe { w.div().bits($conf.div.into_bits()) }
+                .halt()
+                .asserted()
+                .reset()
+                .asserted()
+        });
+        $divreg.modify(|_r, w| w.halt().deasserted().reset().deasserted());
+
+        while $divreg.read().unstab().is_unstable() {}
+
+        Ok($freq / $conf.div.into_divisor())
+    }};
+}
+
+// config types
+
+/// This type represents a divider in the range 1..=16.
+///
+/// At a hardware level, this is an 8-bit register from 0..=15,
+/// which adds one.
+///
+/// While the *clock* domain seems to use 8-bit dividers, the *peripheral* domain
+/// seems to use 4 bit dividers!
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub struct Div4(pub(super) u8);
+
+impl Div4 {
+    /// Divide by one, or no division
+    pub const fn no_div() -> Self {
+        Self(0)
+    }
+
+    /// Store a "raw" divisor value that will divide the source by
+    /// `(n + 1)`, e.g. `Div4::from_raw(0)` will divide the source
+    /// by 1, and `Div4::from_raw(15)` will divide the source by
+    /// 16.
+    pub const fn from_raw(n: u8) -> Option<Self> {
+        if n > 0b1111 { None } else { Some(Self(n)) }
+    }
+
+    /// Store a specific divisor value that will divide the source
+    /// by `n`. e.g. `Div4::from_divisor(1)` will divide the source
+    /// by 1, and `Div4::from_divisor(16)` will divide the source
+    /// by 16.
+    ///
+    /// Will return `None` if `n` is not in the range `1..=16`.
+    /// Consider [`Self::from_raw`] for an infallible version.
+    pub const fn from_divisor(n: u8) -> Option<Self> {
+        let Some(n) = n.checked_sub(1) else {
+            return None;
+        };
+        if n > 0b1111 {
+            return None;
+        }
+        Some(Self(n))
+    }
+
+    /// Convert into "raw" bits form
+    #[inline(always)]
+    pub const fn into_bits(self) -> u8 {
+        self.0
+    }
+
+    /// Convert into "divisor" form, as a u32 for convenient frequency math
+    #[inline(always)]
+    pub const fn into_divisor(self) -> u32 {
+        self.0 as u32 + 1
+    }
+}
+
+/// A basic type that always returns an error when `post_enable_config` is called.
+///
+/// Should only be used as a placeholder.
+pub struct UnimplementedConfig;
+
+impl SPConfHelper for UnimplementedConfig {
+    fn post_enable_config(&self, _clocks: &Clocks) -> Result<u32, ClockError> {
+        Err(ClockError::UnimplementedConfig)
+    }
+}
+
+/// A basic type that always returns `Ok(0)` when `post_enable_config` is called.
+///
+/// This should only be used for peripherals that are "ambiently" clocked, like `PORTn`
+/// peripherals, which have no selectable/configurable source clock.
+pub struct NoConfig;
+impl SPConfHelper for NoConfig {
+    fn post_enable_config(&self, _clocks: &Clocks) -> Result<u32, ClockError> {
+        Ok(0)
+    }
+}
+
+//
+// LPI2c
+//
+
+/// Selectable clocks for `Lpi2c` peripherals
+#[derive(Debug, Clone, Copy)]
+pub enum Lpi2cClockSel {
+    /// FRO12M/FRO_LF/SIRC clock source, passed through divider
+    /// "fro_lf_div"
+    FroLfDiv,
+    /// FRO180M/FRO_HF/FIRC clock source, passed through divider
+    /// "fro_hf_div"
+    FroHfDiv,
+    /// SOSC/XTAL/EXTAL clock source
+    ClkIn,
+    /// clk_1m/FRO_LF divided by 12
+    Clk1M,
+    /// Output of PLL1, passed through clock divider,
+    /// "pll1_clk_div", maybe "pll1_lf_div"?
+    Pll1ClkDiv,
+    /// Disabled
+    None,
+}
+
+/// Which instance of the `Lpi2c` is this?
+///
+/// Should not be directly selectable by end-users.
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum Lpi2cInstance {
+    /// Instance 0
+    Lpi2c0,
+    /// Instance 1
+    Lpi2c1,
+    /// Instance 2
+    Lpi2c2,
+    /// Instance 3
+    Lpi2c3,
+}
+
+/// Top level configuration for `Lpi2c` instances.
+pub struct Lpi2cConfig {
+    /// Power state required for this peripheral
+    pub power: PoweredClock,
+    /// Clock source
+    pub source: Lpi2cClockSel,
+    /// Clock divisor
+    pub div: Div4,
+    /// Which instance is this?
+    // NOTE: should not be user settable
+    pub(crate) instance: Lpi2cInstance,
+}
+
+impl SPConfHelper for Lpi2cConfig {
+    fn post_enable_config(&self, clocks: &Clocks) -> Result<u32, ClockError> {
+        // check that source is suitable
+        let mrcc0 = unsafe { pac::Mrcc0::steal() };
+        use mcxa_pac::mrcc0::mrcc_lpi2c0_clksel::Mux;
+
+        let (clkdiv, clksel) = match self.instance {
+            Lpi2cInstance::Lpi2c0 => (mrcc0.mrcc_lpi2c0_clkdiv(), mrcc0.mrcc_lpi2c0_clksel()),
+            Lpi2cInstance::Lpi2c1 => (mrcc0.mrcc_lpi2c1_clkdiv(), mrcc0.mrcc_lpi2c1_clksel()),
+            Lpi2cInstance::Lpi2c2 => (mrcc0.mrcc_lpi2c2_clkdiv(), mrcc0.mrcc_lpi2c2_clksel()),
+            Lpi2cInstance::Lpi2c3 => (mrcc0.mrcc_lpi2c3_clkdiv(), mrcc0.mrcc_lpi2c3_clksel()),
+        };
+
+        let (freq, variant) = match self.source {
+            Lpi2cClockSel::FroLfDiv => {
+                let freq = clocks.ensure_fro_lf_div_active(&self.power)?;
+                (freq, Mux::ClkrootFunc0)
+            }
+            Lpi2cClockSel::FroHfDiv => {
+                let freq = clocks.ensure_fro_hf_div_active(&self.power)?;
+                (freq, Mux::ClkrootFunc2)
+            }
+            Lpi2cClockSel::ClkIn => {
+                let freq = clocks.ensure_clk_in_active(&self.power)?;
+                (freq, Mux::ClkrootFunc3)
+            }
+            Lpi2cClockSel::Clk1M => {
+                let freq = clocks.ensure_clk_1m_active(&self.power)?;
+                (freq, Mux::ClkrootFunc5)
+            }
+            Lpi2cClockSel::Pll1ClkDiv => {
+                let freq = clocks.ensure_pll1_clk_div_active(&self.power)?;
+                (freq, Mux::ClkrootFunc6)
+            }
+            Lpi2cClockSel::None => unsafe {
+                // no ClkrootFunc7, just write manually for now
+                clksel.write(|w| w.bits(0b111));
+                clkdiv.modify(|_r, w| w.reset().asserted().halt().asserted());
+                return Ok(0);
+            },
+        };
+
+        apply_div4!(self, clksel, clkdiv, variant, freq)
+    }
+}
+
+//
+// LPUart
+//
+
+/// Selectable clocks for Lpuart peripherals
+#[derive(Debug, Clone, Copy)]
+pub enum LpuartClockSel {
+    /// FRO12M/FRO_LF/SIRC clock source, passed through divider
+    /// "fro_lf_div"
+    FroLfDiv,
+    /// FRO180M/FRO_HF/FIRC clock source, passed through divider
+    /// "fro_hf_div"
+    FroHfDiv,
+    /// SOSC/XTAL/EXTAL clock source
+    ClkIn,
+    /// FRO16K/clk_16k source
+    Clk16K,
+    /// clk_1m/FRO_LF divided by 12
+    Clk1M,
+    /// Output of PLL1, passed through clock divider,
+    /// "pll1_clk_div", maybe "pll1_lf_div"?
+    Pll1ClkDiv,
+    /// Disabled
+    None,
+}
+
+/// Which instance of the Lpuart is this?
+///
+/// Should not be directly selectable by end-users.
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum LpuartInstance {
+    /// Instance 0
+    Lpuart0,
+    /// Instance 1
+    Lpuart1,
+    /// Instance 2
+    Lpuart2,
+    /// Instance 3
+    Lpuart3,
+    /// Instance 4
+    Lpuart4,
+    /// Instance 5
+    Lpuart5,
+}
+
+/// Top level configuration for `Lpuart` instances.
+pub struct LpuartConfig {
+    /// Power state required for this peripheral
+    pub power: PoweredClock,
+    /// Clock source
+    pub source: LpuartClockSel,
+    /// Clock divisor
+    pub div: Div4,
+    /// Which instance is this?
+    // NOTE: should not be user settable
+    pub(crate) instance: LpuartInstance,
+}
+
+impl SPConfHelper for LpuartConfig {
+    fn post_enable_config(&self, clocks: &Clocks) -> Result<u32, ClockError> {
+        // check that source is suitable
+        let mrcc0 = unsafe { pac::Mrcc0::steal() };
+        use mcxa_pac::mrcc0::mrcc_lpuart0_clksel::Mux;
+
+        let (clkdiv, clksel) = match self.instance {
+            LpuartInstance::Lpuart0 => (mrcc0.mrcc_lpuart0_clkdiv(), mrcc0.mrcc_lpuart0_clksel()),
+            LpuartInstance::Lpuart1 => (mrcc0.mrcc_lpuart1_clkdiv(), mrcc0.mrcc_lpuart1_clksel()),
+            LpuartInstance::Lpuart2 => (mrcc0.mrcc_lpuart2_clkdiv(), mrcc0.mrcc_lpuart2_clksel()),
+            LpuartInstance::Lpuart3 => (mrcc0.mrcc_lpuart3_clkdiv(), mrcc0.mrcc_lpuart3_clksel()),
+            LpuartInstance::Lpuart4 => (mrcc0.mrcc_lpuart4_clkdiv(), mrcc0.mrcc_lpuart4_clksel()),
+            LpuartInstance::Lpuart5 => (mrcc0.mrcc_lpuart5_clkdiv(), mrcc0.mrcc_lpuart5_clksel()),
+        };
+
+        let (freq, variant) = match self.source {
+            LpuartClockSel::FroLfDiv => {
+                let freq = clocks.ensure_fro_lf_div_active(&self.power)?;
+                (freq, Mux::ClkrootFunc0)
+            }
+            LpuartClockSel::FroHfDiv => {
+                let freq = clocks.ensure_fro_hf_div_active(&self.power)?;
+                (freq, Mux::ClkrootFunc2)
+            }
+            LpuartClockSel::ClkIn => {
+                let freq = clocks.ensure_clk_in_active(&self.power)?;
+                (freq, Mux::ClkrootFunc3)
+            }
+            LpuartClockSel::Clk16K => {
+                let freq = clocks.ensure_clk_16k_vdd_core_active(&self.power)?;
+                (freq, Mux::ClkrootFunc4)
+            }
+            LpuartClockSel::Clk1M => {
+                let freq = clocks.ensure_clk_1m_active(&self.power)?;
+                (freq, Mux::ClkrootFunc5)
+            }
+            LpuartClockSel::Pll1ClkDiv => {
+                let freq = clocks.ensure_pll1_clk_div_active(&self.power)?;
+                (freq, Mux::ClkrootFunc6)
+            }
+            LpuartClockSel::None => unsafe {
+                // no ClkrootFunc7, just write manually for now
+                clksel.write(|w| w.bits(0b111));
+                clkdiv.modify(|_r, w| {
+                    w.reset().asserted();
+                    w.halt().asserted();
+                    w
+                });
+                return Ok(0);
+            },
+        };
+
+        // set clksel
+        apply_div4!(self, clksel, clkdiv, variant, freq)
+    }
+}
+
+//
+// OSTimer
+//
+
+/// Selectable clocks for the OSTimer peripheral
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum OstimerClockSel {
+    /// 16k clock, sourced from FRO16K (Vdd Core)
+    Clk16kVddCore,
+    /// 1 MHz Clock sourced from FRO12M
+    Clk1M,
+    /// Disabled
+    None,
+}
+
+/// Top level configuration for the `OSTimer` peripheral
+pub struct OsTimerConfig {
+    /// Power state required for this peripheral
+    pub power: PoweredClock,
+    /// Selected clock source for this peripheral
+    pub source: OstimerClockSel,
+}
+
+impl SPConfHelper for OsTimerConfig {
+    fn post_enable_config(&self, clocks: &Clocks) -> Result<u32, ClockError> {
+        let mrcc0 = unsafe { pac::Mrcc0::steal() };
+        Ok(match self.source {
+            OstimerClockSel::Clk16kVddCore => {
+                let freq = clocks.ensure_clk_16k_vdd_core_active(&self.power)?;
+                mrcc0.mrcc_ostimer0_clksel().write(|w| w.mux().clkroot_16k());
+                freq
+            }
+            OstimerClockSel::Clk1M => {
+                let freq = clocks.ensure_clk_1m_active(&self.power)?;
+                mrcc0.mrcc_ostimer0_clksel().write(|w| w.mux().clkroot_1m());
+                freq
+            }
+            OstimerClockSel::None => {
+                mrcc0.mrcc_ostimer0_clksel().write(|w| unsafe { w.mux().bits(0b11) });
+                0
+            }
+        })
+    }
+}
+
+//
+// Adc
+//
+
+/// Selectable clocks for the ADC peripheral
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+#[cfg_attr(feature = "defmt", derive(defmt::Format))]
+pub enum AdcClockSel {
+    /// Divided `fro_lf`/`clk_12m`/FRO12M source
+    FroLfDiv,
+    /// Gated `fro_hf`/`FRO180M` source
+    FroHf,
+    /// External Clock Source
+    ClkIn,
+    /// 1MHz clock sourced by a divided `fro_lf`/`clk_12m`
+    Clk1M,
+    /// Internal PLL output, with configurable divisor
+    Pll1ClkDiv,
+    /// No clock/disabled
+    None,
+}
+
+/// Top level configuration for the ADC peripheral
+pub struct AdcConfig {
+    /// Power state required for this peripheral
+    pub power: PoweredClock,
+    /// Selected clock-source for this peripheral
+    pub source: AdcClockSel,
+    /// Pre-divisor, applied to the upstream clock output
+    pub div: Div4,
+}
+
+impl SPConfHelper for AdcConfig {
+    fn post_enable_config(&self, clocks: &Clocks) -> Result<u32, ClockError> {
+        use mcxa_pac::mrcc0::mrcc_adc_clksel::Mux;
+        let mrcc0 = unsafe { pac::Mrcc0::steal() };
+        let (freq, variant) = match self.source {
+            AdcClockSel::FroLfDiv => {
+                let freq = clocks.ensure_fro_lf_div_active(&self.power)?;
+                (freq, Mux::ClkrootFunc0)
+            }
+            AdcClockSel::FroHf => {
+                let freq = clocks.ensure_fro_hf_active(&self.power)?;
+                (freq, Mux::ClkrootFunc1)
+            }
+            AdcClockSel::ClkIn => {
+                let freq = clocks.ensure_clk_in_active(&self.power)?;
+                (freq, Mux::ClkrootFunc3)
+            }
+            AdcClockSel::Clk1M => {
+                let freq = clocks.ensure_clk_1m_active(&self.power)?;
+                (freq, Mux::ClkrootFunc5)
+            }
+            AdcClockSel::Pll1ClkDiv => {
+                let freq = clocks.ensure_pll1_clk_div_active(&self.power)?;
+                (freq, Mux::ClkrootFunc6)
+            }
+            AdcClockSel::None => {
+                mrcc0.mrcc_adc_clksel().write(|w| unsafe {
+                    // no ClkrootFunc7, just write manually for now
+                    w.mux().bits(0b111)
+                });
+                mrcc0.mrcc_adc_clkdiv().modify(|_r, w| {
+                    w.reset().asserted();
+                    w.halt().asserted();
+                    w
+                });
+                return Ok(0);
+            }
+        };
+        let clksel = mrcc0.mrcc_adc_clksel();
+        let clkdiv = mrcc0.mrcc_adc_clkdiv();
+
+        apply_div4!(self, clksel, clkdiv, variant, freq)
+    }
+}