Add MCO support

examples/mco.rs

@@ -0,0 +1,40 @@
+//! Configure the MCO (Microcontroller Clock Output) to give a 2MHz signal on PA8 and PA9, sourced
+//! from the internal HSI16 16MHz oscillator.
+
+#![deny(unsafe_code)]
+#![no_main]
+#![no_std]
+
+extern crate panic_halt;
+
+use cortex_m_rt::entry;
+use stm32l0xx_hal::{
+    pac::{
+        self,
+        rcc::cfgr::{MCOPRE_A, MCOSEL_A},
+    },
+    prelude::*,
+    rcc::Config,
+};
+
+#[entry]
+fn main() -> ! {
+    let dp = pac::Peripherals::take().unwrap();
+
+    // Configure the 16MHz internal clock
+    let mut rcc = dp.RCC.freeze(Config::hsi16());
+
+    let gpioa = dp.GPIOA.split(&mut rcc);
+
+    // Source MCO from HSI16, configure prescaler to divide by 8 to get 2MHz output.
+    rcc.configure_mco(MCOSEL_A::HSI16, MCOPRE_A::DIV8, (gpioa.pa8, gpioa.pa9));
+
+    // Individual pins can also be set by passing them directly:
+    // rcc.enable_mco(MCOSEL_A::HSI16, MCOPRE_A::DIV8, gpioa.pa8);
+
+    // Or for larger devices, all 3 MCO pins can be configured:
+    // rcc.configure_mco(MCOSEL_A::HSI16, MCOPRE_A::DIV8, (gpioa.pa8, gpioa.pa9, gpiob.pb13));
+
+    // Probe PA8 or PA9 to see generated 2MHz MCO signal.
+    loop {}
+}

src/lib.rs

@@ -40,6 +40,7 @@ pub mod gpio;
 ))]
 pub mod i2c;
 pub mod lptim;
+pub mod mco;
 pub mod prelude;
 pub mod pwm;
 pub mod pwr;

src/mco.rs

@@ -0,0 +1,52 @@
+//! MCO (Microcontroller Clock Output)
+//!
+//! MCO is available on PA8 or PA9. See "Table 16. Alternate function port A" in the datasheet.
+
+use crate::gpio::{gpioa, gpiob, AltMode, Analog};
+
+pub trait Pin {
+    fn into_mco(self);
+}
+
+impl Pin for gpioa::PA8<Analog> {
+    fn into_mco(self) {
+        self.set_alt_mode(AltMode::AF0);
+    }
+}
+
+impl Pin for gpioa::PA9<Analog> {
+    fn into_mco(self) {
+        self.set_alt_mode(AltMode::AF0);
+    }
+}
+
+impl Pin for gpiob::PB13<Analog> {
+    fn into_mco(self) {
+        self.set_alt_mode(AltMode::AF2);
+    }
+}
+
+// Blanket impls to allow configuration of all MCO pins.
+impl<P1, P2> Pin for (P1, P2)
+where
+    P1: Pin,
+    P2: Pin,
+{
+    fn into_mco(self) {
+        self.0.into_mco();
+        self.1.into_mco();
+    }
+}
+
+impl<P1, P2, P3> Pin for (P1, P2, P3)
+where
+    P1: Pin,
+    P2: Pin,
+    P3: Pin,
+{
+    fn into_mco(self) {
+        self.0.into_mco();
+        self.1.into_mco();
+        self.2.into_mco();
+    }
+}

src/rcc.rs

@@ -1,3 +1,5 @@
+use crate::mco;
+use crate::pac::rcc::cfgr::{MCOPRE_A, MCOSEL_A};
 use crate::pac::RCC;
 use crate::time::{Hertz, U32Ext};
 
@@ -226,6 +228,28 @@ impl Rcc {
     }
 }
 
+impl Rcc {
+    /// Configure MCO (Microcontroller Clock Output).
+    pub fn configure_mco<P>(
+        &mut self,
+        source: MCOSEL_A,
+        prescaler: MCOPRE_A,
+        output_pin: P,
+    ) -> MCOEnabled
+    where
+        P: mco::Pin,
+    {
+        output_pin.into_mco();
+
+        self.rb.cfgr.modify(|_, w| {
+            w.mcosel().variant(source);
+            w.mcopre().variant(prescaler)
+        });
+
+        MCOEnabled(())
+    }
+}
+
 /// Extension trait that freezes the `RCC` peripheral with provided clocks configuration
 pub trait RccExt {
     fn freeze(self, config: Config) -> Rcc;
@@ -425,3 +449,9 @@ impl Clocks {
 /// You can get an instance of this struct by calling [`Rcc::enable_hsi48`].
 #[derive(Clone, Copy)]
 pub struct HSI48(());
+
+/// Token that exists only if MCO (Microcontroller Clock Out) has been enabled.
+///
+/// You can get an instance of this struct by calling [`Rcc::configure_mco`].
+#[derive(Clone, Copy)]
+pub struct MCOEnabled(());