Add RTC timer for stm32f4

7 files changed, 494 insertions, 4 deletions

diff --git a/embassy-stm32f4-examples/.cargo/config b/embassy-stm32f4-examples/.cargo/config
index 707494d68..836853988 100644
--- a/embassy-stm32f4-examples/.cargo/config
+++ b/embassy-stm32f4-examples/.cargo/config
@@ -1,5 +1,5 @@
 [target.'cfg(all(target_arch = "arm", target_os = "none"))']
-runner = "probe-run --chip STM32F411CEUx --defmt"
+runner = "probe-run --chip STM32F401CCUx --defmt"
 
 rustflags = [
   # LLD (shipped with the Rust toolchain) is used as the default linker
diff --git a/embassy-stm32f4-examples/Cargo.toml b/embassy-stm32f4-examples/Cargo.toml
index e81f85ff1..216964374 100644
--- a/embassy-stm32f4-examples/Cargo.toml
+++ b/embassy-stm32f4-examples/Cargo.toml
@@ -18,7 +18,7 @@ defmt-error = []
 
 [dependencies]
 embassy = { version = "0.1.0", path = "../embassy", features = ["defmt", "defmt-trace"] }
-embassy-stm32f4 = { version = "*", path = "../embassy-stm32f4", features = ["stm32f405"] }
+embassy-stm32f4 = { version = "*", path = "../embassy-stm32f4", features = ["stm32f401"] }
 
 defmt = "0.1.3"
 defmt-rtt = "0.1.0"
@@ -27,6 +27,6 @@ cortex-m = "0.7.1"
 cortex-m-rt = "0.6.13"
 embedded-hal    = { version = "0.2.4" }
 panic-probe = "0.1.0"
-stm32f4xx-hal  = { version = "0.8.3", features = ["rt", "stm32f405"], git = "https://github.com/stm32-rs/stm32f4xx-hal.git"}
+stm32f4xx-hal  = { version = "0.8.3", features = ["rt", "stm32f401"], git = "https://github.com/stm32-rs/stm32f4xx-hal.git"}
 futures = { version = "0.3.8", default-features = false, features = ["async-await"] }
 rtt-target = { version = "0.3", features = ["cortex-m"] }
diff --git a/embassy-stm32f4-examples/memory.x b/embassy-stm32f4-examples/memory.x
index ee4d4d59c..efa700b8a 100644
--- a/embassy-stm32f4-examples/memory.x
+++ b/embassy-stm32f4-examples/memory.x
@@ -1,5 +1,5 @@
 MEMORY
 {
-  FLASH : ORIGIN = 0x08000000, LENGTH = 64K 
+  FLASH : ORIGIN = 0x08000000, LENGTH = 64K
   RAM : ORIGIN = 0x20000000, LENGTH = 32K
 }
diff --git a/embassy-stm32f4-examples/src/bin/rtc_async.rs b/embassy-stm32f4-examples/src/bin/rtc_async.rs
new file mode 100644
index 000000000..e53212263
--- /dev/null
+++ b/embassy-stm32f4-examples/src/bin/rtc_async.rs
@@ -0,0 +1,65 @@
+#![no_std]
+#![no_main]
+#![feature(type_alias_impl_trait)]
+
+#[path = "../example_common.rs"]
+mod example_common;
+use example_common::*;
+
+use cortex_m_rt::entry;
+use defmt::panic;
+use embassy::executor::{task, Executor};
+use embassy::time::{Duration, Timer};
+use embassy::util::Forever;
+use embassy_stm32f4::{interrupt, pac, rtc};
+use stm32f4xx_hal::prelude::*;
+
+#[task]
+async fn run1() {
+    loop {
+        info!("BIG INFREQUENT TICK");
+        Timer::after(Duration::from_ticks(32768 * 2)).await;
+    }
+}
+
+#[task]
+async fn run2() {
+    loop {
+        info!("tick");
+        Timer::after(Duration::from_ticks(13000)).await;
+    }
+}
+
+static RTC: Forever<rtc::RTC<pac::TIM2>> = Forever::new();
+static ALARM: Forever<rtc::Alarm<pac::TIM2>> = Forever::new();
+static EXECUTOR: Forever<Executor> = Forever::new();
+
+#[entry]
+fn main() -> ! {
+    info!("Hello World!");
+
+    let p = unwrap!(pac::Peripherals::take());
+
+    p.RCC.ahb1enr.modify(|_, w| w.dma1en().enabled());
+    let rcc = p.RCC.constrain();
+    let clocks = rcc.cfgr.freeze();
+
+    p.DBGMCU.cr.modify(|_, w| {
+        w.dbg_sleep().set_bit();
+        w.dbg_standby().set_bit();
+        w.dbg_stop().set_bit()
+    });
+
+    let rtc = RTC.put(rtc::RTC::new(p.TIM2, interrupt::take!(TIM2), clocks));
+    rtc.start();
+
+    unsafe { embassy::time::set_clock(rtc) };
+
+    let alarm = ALARM.put(rtc.alarm1());
+    let executor = EXECUTOR.put(Executor::new());
+    executor.set_alarm(alarm);
+    executor.run(|spawner| {
+        unwrap!(spawner.spawn(run1()));
+        unwrap!(spawner.spawn(run2()));
+    });
+}
diff --git a/embassy-stm32f4/src/interrupt.rs b/embassy-stm32f4/src/interrupt.rs
index c75e4b82d..8336df7d2 100644
--- a/embassy-stm32f4/src/interrupt.rs
+++ b/embassy-stm32f4/src/interrupt.rs
@@ -94,6 +94,66 @@ where
     }
 }
 
+#[cfg(feature = "stm32f401")]
+mod irqs {
+    use super::*;
+    declare!(PVD);
+    declare!(TAMP_STAMP);
+    declare!(RTC_WKUP);
+    declare!(FLASH);
+    declare!(RCC);
+    declare!(EXTI0);
+    declare!(EXTI1);
+    declare!(EXTI2);
+    declare!(EXTI3);
+    declare!(EXTI4);
+    declare!(DMA1_STREAM0);
+    declare!(DMA1_STREAM1);
+    declare!(DMA1_STREAM2);
+    declare!(DMA1_STREAM3);
+    declare!(DMA1_STREAM4);
+    declare!(DMA1_STREAM5);
+    declare!(DMA1_STREAM6);
+    declare!(ADC);
+    declare!(EXTI9_5);
+    declare!(TIM1_BRK_TIM9);
+    declare!(TIM1_UP_TIM10);
+    declare!(TIM1_TRG_COM_TIM11);
+    declare!(TIM1_CC);
+    declare!(TIM2);
+    declare!(TIM3);
+    declare!(TIM4);
+    declare!(I2C1_EV);
+    declare!(I2C1_ER);
+    declare!(I2C2_EV);
+    declare!(I2C2_ER);
+    declare!(SPI1);
+    declare!(SPI2);
+    declare!(USART1);
+    declare!(USART2);
+    declare!(EXTI15_10);
+    declare!(RTC_ALARM);
+    declare!(OTG_FS_WKUP);
+    declare!(DMA1_STREAM7);
+    declare!(SDIO);
+    declare!(TIM5);
+    declare!(SPI3);
+    declare!(DMA2_STREAM0);
+    declare!(DMA2_STREAM1);
+    declare!(DMA2_STREAM2);
+    declare!(DMA2_STREAM3);
+    declare!(DMA2_STREAM4);
+    declare!(OTG_FS);
+    declare!(DMA2_STREAM5);
+    declare!(DMA2_STREAM6);
+    declare!(DMA2_STREAM7);
+    declare!(USART6);
+    declare!(I2C3_EV);
+    declare!(I2C3_ER);
+    declare!(FPU);
+    declare!(SPI4);
+}
+
 #[cfg(feature = "stm32f405")]
 mod irqs {
     use super::*;
diff --git a/embassy-stm32f4/src/lib.rs b/embassy-stm32f4/src/lib.rs
index 02668b7eb..eb8530ea2 100644
--- a/embassy-stm32f4/src/lib.rs
+++ b/embassy-stm32f4/src/lib.rs
@@ -312,6 +312,7 @@ pub(crate) mod fmt;
 
 pub mod exti;
 pub mod interrupt;
+pub mod rtc;
 pub mod serial;
 
 pub use cortex_m_rt::interrupt;
diff --git a/embassy-stm32f4/src/rtc.rs b/embassy-stm32f4/src/rtc.rs
new file mode 100644
index 000000000..7dc3a563f
--- /dev/null
+++ b/embassy-stm32f4/src/rtc.rs
@@ -0,0 +1,364 @@
+use core::cell::Cell;
+use core::convert::TryInto;
+use core::sync::atomic::{compiler_fence, AtomicU32, Ordering};
+
+use embassy::time::{Clock, TICKS_PER_SECOND};
+use stm32f4xx_hal::bb;
+use stm32f4xx_hal::rcc::Clocks;
+
+use crate::interrupt;
+use crate::interrupt::{CriticalSection, Mutex, OwnedInterrupt};
+
+// RTC timekeeping works with something we call "periods", which are time intervals
+// of 2^15 ticks. The RTC counter value is 16 bits, so one "overflow cycle" is 2 periods.
+//
+// A `period` count is maintained in parallel to the RTC hardware `counter`, like this:
+// - `period` and `counter` start at 0
+// - `period` is incremented on overflow (at counter value 0)
+// - `period` is incremented "midway" between overflows (at counter value 0x8000)
+//
+// Therefore, when `period` is even, counter is in 0..0x7FFF. When odd, counter is in 0x8000..0xFFFF
+// This allows for now() to return the correct value even if it races an overflow.
+//
+// To get `now()`, `period` is read first, then `counter` is read. If the counter value matches
+// the expected range for the `period` parity, we're done. If it doesn't, this means that
+// a new period start has raced us between reading `period` and `counter`, so we assume the `counter` value
+// corresponds to the next period.
+//
+// `period` is a 32bit integer, so It overflows on 2^32 * 2^15 / 32768 seconds of uptime, which is 136 years.
+
+fn calc_now(period: u32, counter: u16) -> u64 {
+    ((period as u64) << 15) + ((counter as u32 ^ ((period & 1) << 15)) as u64)
+}
+
+struct AlarmState {
+    timestamp: Cell<u64>,
+    callback: Cell<Option<(fn(*mut ()), *mut ())>>,
+}
+
+impl AlarmState {
+    fn new() -> Self {
+        Self {
+            timestamp: Cell::new(u64::MAX),
+            callback: Cell::new(None),
+        }
+    }
+}
+
+// TODO: This is sometimes wasteful, try to find a better way
+const ALARM_COUNT: usize = 3;
+
+pub struct RTC<T: Instance> {
+    rtc: T,
+    irq: T::Interrupt,
+
+    /// Number of 2^23 periods elapsed since boot.
+    period: AtomicU32,
+
+    /// Timestamp at which to fire alarm. u64::MAX if no alarm is scheduled.
+    alarms: Mutex<[AlarmState; ALARM_COUNT]>,
+
+    clocks: Clocks,
+}
+
+impl<T: Instance> RTC<T> {
+    pub fn new(rtc: T, irq: T::Interrupt, clocks: Clocks) -> Self {
+        Self {
+            rtc,
+            irq,
+            period: AtomicU32::new(0),
+            alarms: Mutex::new([AlarmState::new(), AlarmState::new(), AlarmState::new()]),
+            clocks,
+        }
+    }
+
+    pub fn start(&'static self) {
+        self.rtc.enable_clock();
+        self.rtc.stop_and_reset();
+
+        let multiplier = if T::ppre(&self.clocks) == 1 { 1 } else { 2 };
+        let freq = T::pclk(&self.clocks) * multiplier;
+        let psc = freq / TICKS_PER_SECOND as u32 - 1;
+        let psc: u16 = psc.try_into().unwrap();
+
+        self.rtc.set_psc_arr(psc, u16::MAX);
+        // Mid-way point
+        self.rtc.set_compare(0, 0x8000);
+        self.rtc.set_compare_interrupt(0, true);
+
+        self.irq.set_handler(
+            |ptr| unsafe {
+                let this = &*(ptr as *const () as *const Self);
+                this.on_interrupt();
+            },
+            self as *const _ as *mut _,
+        );
+        self.irq.unpend();
+        self.irq.enable();
+
+        self.rtc.start();
+    }
+
+    fn on_interrupt(&self) {
+        if self.rtc.overflow_interrupt_status() {
+            self.rtc.overflow_clear_flag();
+            self.next_period();
+        }
+
+        // Half overflow
+        if self.rtc.compare_interrupt_status(0) {
+            self.rtc.compare_clear_flag(0);
+            self.next_period();
+        }
+
+        for n in 1..=ALARM_COUNT {
+            if self.rtc.compare_interrupt_status(n) {
+                self.rtc.compare_clear_flag(n);
+                interrupt::free(|cs| self.trigger_alarm(n, cs));
+            }
+        }
+    }
+
+    fn next_period(&self) {
+        interrupt::free(|cs| {
+            let period = self.period.fetch_add(1, Ordering::Relaxed) + 1;
+            let t = (period as u64) << 15;
+
+            for n in 1..=ALARM_COUNT {
+                let alarm = &self.alarms.borrow(cs)[n - 1];
+                let at = alarm.timestamp.get();
+
+                let diff = at - t;
+                if diff < 0xc000 {
+                    self.rtc.set_compare(n, at as u16);
+                    self.rtc.set_compare_interrupt(n, true);
+                }
+            }
+        })
+    }
+
+    fn trigger_alarm(&self, n: usize, cs: &CriticalSection) {
+        self.rtc.set_compare_interrupt(n, false);
+
+        let alarm = &self.alarms.borrow(cs)[n - 1];
+        alarm.timestamp.set(u64::MAX);
+
+        // Call after clearing alarm, so the callback can set another alarm.
+        if let Some((f, ctx)) = alarm.callback.get() {
+            f(ctx);
+        }
+    }
+
+    fn set_alarm_callback(&self, n: usize, callback: fn(*mut ()), ctx: *mut ()) {
+        interrupt::free(|cs| {
+            let alarm = &self.alarms.borrow(cs)[n - 1];
+            alarm.callback.set(Some((callback, ctx)));
+        })
+    }
+
+    fn set_alarm(&self, n: usize, timestamp: u64) {
+        interrupt::free(|cs| {
+            let alarm = &self.alarms.borrow(cs)[n - 1];
+            alarm.timestamp.set(timestamp);
+
+            let t = self.now();
+            if timestamp <= t {
+                self.trigger_alarm(n, cs);
+                return;
+            }
+
+            let diff = timestamp - t;
+            if diff < 0xc000 {
+                let safe_timestamp = timestamp.max(t + 3);
+                self.rtc.set_compare(n, safe_timestamp as u16);
+                self.rtc.set_compare_interrupt(n, true);
+            } else {
+                self.rtc.set_compare_interrupt(n, false);
+            }
+        })
+    }
+
+    pub fn alarm1(&'static self) -> Alarm<T> {
+        Alarm { n: 1, rtc: self }
+    }
+    pub fn alarm2(&'static self) -> Option<Alarm<T>> {
+        if T::REAL_ALARM_COUNT >= 2 {
+            Some(Alarm { n: 2, rtc: self })
+        } else {
+            None
+        }
+    }
+    pub fn alarm3(&'static self) -> Option<Alarm<T>> {
+        if T::REAL_ALARM_COUNT >= 3 {
+            Some(Alarm { n: 3, rtc: self })
+        } else {
+            None
+        }
+    }
+}
+
+impl<T: Instance> embassy::time::Clock for RTC<T> {
+    fn now(&self) -> u64 {
+        let period = self.period.load(Ordering::Relaxed);
+        compiler_fence(Ordering::Acquire);
+        let counter = self.rtc.counter();
+        calc_now(period, counter)
+    }
+}
+
+pub struct Alarm<T: Instance> {
+    n: usize,
+    rtc: &'static RTC<T>,
+}
+
+impl<T: Instance> embassy::time::Alarm for Alarm<T> {
+    fn set_callback(&self, callback: fn(*mut ()), ctx: *mut ()) {
+        self.rtc.set_alarm_callback(self.n, callback, ctx);
+    }
+
+    fn set(&self, timestamp: u64) {
+        self.rtc.set_alarm(self.n, timestamp);
+    }
+
+    fn clear(&self) {
+        self.rtc.set_alarm(self.n, u64::MAX);
+    }
+}
+
+mod sealed {
+    pub trait Sealed {}
+}
+
+pub trait Instance: sealed::Sealed + Sized + 'static {
+    type Interrupt: OwnedInterrupt;
+    const REAL_ALARM_COUNT: usize;
+
+    fn enable_clock(&self);
+    fn set_compare(&self, n: usize, value: u16);
+    fn set_compare_interrupt(&self, n: usize, enable: bool);
+    fn compare_interrupt_status(&self, n: usize) -> bool;
+    fn compare_clear_flag(&self, n: usize);
+    fn overflow_interrupt_status(&self) -> bool;
+    fn overflow_clear_flag(&self);
+    fn set_psc_arr(&self, psc: u16, arr: u16);
+    fn stop_and_reset(&self);
+    fn start(&self);
+    fn counter(&self) -> u16;
+    fn ppre(clocks: &Clocks) -> u8;
+    fn pclk(clocks: &Clocks) -> u32;
+}
+
+mod tim2 {
+    use super::*;
+    use stm32f4xx_hal::pac::{RCC, TIM2};
+
+    impl sealed::Sealed for TIM2 {}
+
+    impl Instance for TIM2 {
+        type Interrupt = interrupt::TIM2Interrupt;
+        const REAL_ALARM_COUNT: usize = 3;
+
+        fn enable_clock(&self) {
+            // NOTE(unsafe) It will only be used for atomic operations
+            unsafe {
+                let rcc = &*RCC::ptr();
+
+                bb::set(&rcc.apb1enr, 0);
+                bb::set(&rcc.apb1rstr, 0);
+                bb::clear(&rcc.apb1rstr, 0);
+            }
+        }
+
+        fn set_compare(&self, n: usize, value: u16) {
+            // NOTE(unsafe) these registers accept all the range of u16 values
+            match n {
+                0 => self.ccr1.write(|w| unsafe { w.bits(value.into()) }),
+                1 => self.ccr2.write(|w| unsafe { w.bits(value.into()) }),
+                2 => self.ccr3.write(|w| unsafe { w.bits(value.into()) }),
+                3 => self.ccr4.write(|w| unsafe { w.bits(value.into()) }),
+                _ => {}
+            }
+        }
+
+        fn set_compare_interrupt(&self, n: usize, enable: bool) {
+            if n > 3 {
+                return;
+            }
+            let bit = n as u8 + 1;
+            unsafe {
+                if enable {
+                    bb::set(&self.dier, bit);
+                } else {
+                    bb::clear(&self.dier, bit);
+                }
+            }
+        }
+
+        fn compare_interrupt_status(&self, n: usize) -> bool {
+            let status = self.sr.read();
+            match n {
+                0 => status.cc1if().bit_is_set(),
+                1 => status.cc2if().bit_is_set(),
+                2 => status.cc3if().bit_is_set(),
+                3 => status.cc4if().bit_is_set(),
+                _ => false,
+            }
+        }
+
+        fn compare_clear_flag(&self, n: usize) {
+            if n > 3 {
+                return;
+            }
+            let bit = n as u8 + 1;
+            unsafe {
+                bb::clear(&self.sr, bit);
+            }
+        }
+
+        fn overflow_interrupt_status(&self) -> bool {
+            self.sr.read().uif().bit_is_set()
+        }
+
+        fn overflow_clear_flag(&self) {
+            unsafe {
+                bb::clear(&self.sr, 0);
+            }
+        }
+
+        fn set_psc_arr(&self, psc: u16, arr: u16) {
+            // NOTE(unsafe) All u16 values are valid
+            self.psc.write(|w| unsafe { w.bits(psc.into()) });
+            self.arr.write(|w| unsafe { w.bits(arr.into()) });
+
+            unsafe {
+                // Set URS, generate update, clear URS
+                bb::set(&self.cr1, 2);
+                self.egr.write(|w| w.ug().set_bit());
+                bb::clear(&self.cr1, 2);
+            }
+        }
+
+        fn stop_and_reset(&self) {
+            unsafe {
+                bb::clear(&self.cr1, 0);
+            }
+            self.cnt.reset();
+        }
+
+        fn start(&self) {
+            unsafe { bb::set(&self.cr1, 0) }
+        }
+
+        fn counter(&self) -> u16 {
+            self.cnt.read().bits() as u16
+        }
+
+        fn ppre(clocks: &Clocks) -> u8 {
+            clocks.ppre1()
+        }
+
+        fn pclk(clocks: &Clocks) -> u32 {
+            clocks.pclk1().0
+        }
+    }
+}