gpio: add EXTI support (#21)

Add EXTI support to GPIO module.

This is taken directly from the implementation in
[stm32h7xx-hal](https://github.com/stm32-rs/stm32h7xx-hal).

src/gpio.rs

@@ -44,6 +44,7 @@
 //! ownership reasons, you can use the closure based `with_<mode>` functions to temporarily change the pin type, do
 //! some output or input, and then have it change back once done.
 
+mod exti;
 mod gpio_def;
 
 use core::{fmt, marker::PhantomData};
@@ -52,6 +53,7 @@ pub use embedded_hal::digital::PinState;
 
 use crate::rcc::ResetEnable;
 
+pub use exti::ExtiPin;
 pub use gpio_def::*;
 
 /// A filler pin type
@@ -152,7 +154,6 @@ pub type Debugger = Alternate<0, PushPull>;
 
 mod marker {
     /// Marker trait that show if `ExtiPin` can be implemented
-    #[allow(dead_code)] // TODO: Remove when EXTI is implemented
     pub trait Interruptable {}
     /// Marker trait for readable pin modes
     pub trait Readable {}

src/gpio/exti.rs

@@ -0,0 +1,164 @@
+use super::{marker, Edge, Pin, PinExt};
+use crate::pac::{Interrupt, EXTI};
+
+impl<const P: char, const N: u8, MODE> Pin<P, N, MODE> {
+    /// NVIC interrupt number of interrupt from this pin
+    ///
+    /// Used to unmask / enable the interrupt with [`cortex_m::peripheral::NVIC::unmask()`].
+    /// This is also useful for all other [`cortex_m::peripheral::NVIC`] functions.
+    pub const fn interrupt(&self) -> Interrupt {
+        match N {
+            0 => Interrupt::EXTI0,
+            1 => Interrupt::EXTI1,
+            2 => Interrupt::EXTI2,
+            3 => Interrupt::EXTI3,
+            4 => Interrupt::EXTI4,
+            5 => Interrupt::EXTI5,
+            6 => Interrupt::EXTI6,
+            7 => Interrupt::EXTI7,
+            8 => Interrupt::EXTI8,
+            9 => Interrupt::EXTI9,
+            10 => Interrupt::EXTI10,
+            11 => Interrupt::EXTI11,
+            12 => Interrupt::EXTI12,
+            13 => Interrupt::EXTI13,
+            14 => Interrupt::EXTI14,
+            15 => Interrupt::EXTI15,
+            _ => panic!("Unsupported pin number"),
+        }
+    }
+}
+
+/// External Interrupt Pin
+pub trait ExtiPin {
+    fn make_interrupt_source(&mut self, exti: &mut EXTI);
+    fn trigger_on_edge(&mut self, exti: &mut EXTI, level: Edge);
+    fn enable_event(&mut self, exti: &mut EXTI);
+    fn disable_event(&mut self, exti: &mut EXTI);
+    fn enable_interrupt(&mut self, exti: &mut EXTI);
+    fn disable_interrupt(&mut self, exti: &mut EXTI);
+    fn clear_interrupt_pending_bit(&mut self, edge: Edge);
+    fn check_interrupt(&self, edge: Edge) -> bool;
+}
+
+impl<PIN> ExtiPin for PIN
+where
+    PIN: PinExt,
+    PIN::Mode: marker::Interruptable,
+{
+    /// Make corresponding EXTI line sensitive to this pin
+    #[inline(always)]
+    fn make_interrupt_source(&mut self, exti: &mut EXTI) {
+        let i = self.pin_id();
+        let port = self.port_id() as u32;
+        let offset = 8 * (i % 4);
+        match i {
+            0..=3 => {
+                exti.exticr1().modify(|r, w| unsafe {
+                    w.bits((r.bits() & !(0xf << offset)) | (port << offset))
+                });
+            }
+            4..=7 => {
+                exti.exticr2().modify(|r, w| unsafe {
+                    w.bits((r.bits() & !(0xf << offset)) | (port << offset))
+                });
+            }
+            8..=11 => {
+                exti.exticr3().modify(|r, w| unsafe {
+                    w.bits((r.bits() & !(0xf << offset)) | (port << offset))
+                });
+            }
+            12..=15 => {
+                exti.exticr4().modify(|r, w| unsafe {
+                    w.bits((r.bits() & !(0xf << offset)) | (port << offset))
+                });
+            }
+            _ => unreachable!(),
+        }
+    }
+
+    /// Generate interrupt on rising edge, falling edge or both
+    #[inline(always)]
+    fn trigger_on_edge(&mut self, exti: &mut EXTI, edge: Edge) {
+        let i = self.pin_id();
+        match edge {
+            Edge::Rising => {
+                exti.rtsr1()
+                    .modify(|r, w| unsafe { w.bits(r.bits() | (1 << i)) });
+                exti.ftsr1()
+                    .modify(|r, w| unsafe { w.bits(r.bits() & !(1 << i)) });
+            }
+            Edge::Falling => {
+                exti.ftsr1()
+                    .modify(|r, w| unsafe { w.bits(r.bits() | (1 << i)) });
+                exti.rtsr1()
+                    .modify(|r, w| unsafe { w.bits(r.bits() & !(1 << i)) });
+            }
+            Edge::RisingFalling => {
+                exti.rtsr1()
+                    .modify(|r, w| unsafe { w.bits(r.bits() | (1 << i)) });
+                exti.ftsr1()
+                    .modify(|r, w| unsafe { w.bits(r.bits() | (1 << i)) });
+            }
+        }
+    }
+
+    /// Enable external interrupts from this pin.
+    #[inline(always)]
+    fn enable_event(&mut self, exti: &mut EXTI) {
+        exti.emr1()
+            .modify(|r, w| unsafe { w.bits(r.bits() | (1 << self.pin_id())) });
+    }
+
+    /// Disable external interrupts from this pin
+    #[inline(always)]
+    fn disable_event(&mut self, exti: &mut EXTI) {
+        exti.emr1()
+            .modify(|r, w| unsafe { w.bits(r.bits() & !(1 << self.pin_id())) });
+    }
+
+    /// Enable external interrupts from this pin.
+    #[inline(always)]
+    fn enable_interrupt(&mut self, exti: &mut EXTI) {
+        exti.imr1()
+            .modify(|r, w| unsafe { w.bits(r.bits() | (1 << self.pin_id())) });
+    }
+
+    /// Disable external interrupts from this pin
+    #[inline(always)]
+    fn disable_interrupt(&mut self, exti: &mut EXTI) {
+        exti.imr1()
+            .modify(|r, w| unsafe { w.bits(r.bits() & !(1 << self.pin_id())) });
+    }
+
+    /// Clear the interrupt pending bit for this pin
+    #[inline(always)]
+    fn clear_interrupt_pending_bit(&mut self, edge: Edge) {
+        unsafe {
+            let exti = &(*EXTI::ptr());
+
+            let mask = 1 << self.pin_id();
+            match edge {
+                Edge::Rising => exti.rpr1().write(|w| w.bits(mask)),
+                Edge::Falling => exti.fpr1().write(|w| w.bits(mask)),
+                _ => panic!("Must choose a rising or falling edge"),
+            }
+        }
+    }
+
+    /// Reads the interrupt pending bit for this pin
+    #[inline(always)]
+    fn check_interrupt(&self, edge: Edge) -> bool {
+        unsafe {
+            let exti = &(*EXTI::ptr());
+
+            let bits = match edge {
+                Edge::Rising => exti.rpr1().read().bits(),
+                Edge::Falling => exti.fpr1().read().bits(),
+                _ => panic!("Must choose a rising or falling edge"),
+            };
+
+            bits & (1 << self.pin_id()) != 0
+        }
+    }
+}