wip timers for embassy rtc

2 files changed, 587 insertions, 0 deletions

diff --git a/embassy-stm32/src/lib.rs b/embassy-stm32/src/lib.rs
index 8f8dd753b..7bcae9f90 100644
--- a/embassy-stm32/src/lib.rs
+++ b/embassy-stm32/src/lib.rs
@@ -17,6 +17,8 @@ pub mod pwr;
 pub mod rcc;
 #[cfg(feature = "_rng")]
 pub mod rng;
+#[cfg(feature = "_timer")]
+pub mod rtc;
 #[cfg(feature = "_sdmmc")]
 pub mod sdmmc;
 #[cfg(feature = "_spi")]
diff --git a/embassy-stm32/src/rtc.rs b/embassy-stm32/src/rtc.rs
new file mode 100644
index 000000000..1ccac0e2d
--- /dev/null
+++ b/embassy-stm32/src/rtc.rs
@@ -0,0 +1,585 @@
+use core::cell::Cell;
+use core::convert::TryInto;
+use core::sync::atomic::{compiler_fence, AtomicU32, Ordering};
+
+use embassy::interrupt::InterruptExt;
+use embassy::time::{Clock, TICKS_PER_SECOND};
+use embassy::util::AtomicWaker;
+
+use crate::interrupt::{CriticalSection, Interrupt, Mutex};
+use crate::pac::timer::TimGp16;
+use crate::time::Hertz;
+
+// 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>,
+    #[allow(clippy::type_complexity)]
+    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;
+
+/// RTC timer that can be used by the executor and to set alarms.
+///
+/// It can work with Timers 2, 3, 4, 5, 9 and 12. Timers 9 and 12 only have one alarm available,
+/// while the others have three each.
+/// This timer works internally with a unit of 2^15 ticks, which means that if a call to
+/// [`embassy::time::Clock::now`] is blocked for that amount of ticks the returned value will be
+/// wrong (an old value). The current default tick rate is 32768 ticks per second.
+pub struct RTC<T: Instance> {
+    _inner: 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]>,
+}
+
+impl<T: Instance> RTC<T> {
+    pub fn new(peripheral: T, irq: T::Interrupt) -> Self {
+        Self {
+            _inner: peripheral,
+            irq,
+            period: AtomicU32::new(0),
+            alarms: Mutex::new([AlarmState::new(), AlarmState::new(), AlarmState::new()]),
+        }
+    }
+
+    pub fn start(&'static self, pfreq: Hertz, ppre: u8) {
+        let inner = T::inner();
+
+        // NOTE(unsafe) Critical section to use the unsafe methods
+        critical_section::with(|_| {
+            unsafe {
+                inner.prepare(pfreq, ppre);
+            }
+
+            self.irq.set_handler_context(self as *const _ as *mut _);
+            self.irq.set_handler(|ptr| unsafe {
+                let this = &*(ptr as *const () as *const Self);
+                this.on_interrupt();
+            });
+            self.irq.unpend();
+            self.irq.enable();
+
+            unsafe {
+                inner.start_counter();
+            }
+        })
+    }
+
+    fn on_interrupt(&self) {
+        let inner = T::inner();
+
+        // NOTE(unsafe) Use critical section to access the methods
+        // XXX: reduce the size of this critical section ?
+        critical_section::with(|cs| unsafe {
+            if inner.overflow_interrupt_status() {
+                inner.overflow_clear_flag();
+                self.next_period();
+            }
+
+            // Half overflow
+            if inner.compare_interrupt_status(0) {
+                inner.compare_clear_flag(0);
+                self.next_period();
+            }
+
+            for n in 1..=ALARM_COUNT {
+                if inner.compare_interrupt_status(n) {
+                    inner.compare_clear_flag(n);
+                    self.trigger_alarm(n, cs);
+                }
+            }
+        })
+    }
+
+    fn next_period(&self) {
+        let inner = T::inner();
+
+        let period = self.period.fetch_add(1, Ordering::Relaxed) + 1;
+        let t = (period as u64) << 15;
+
+        critical_section::with(move |cs| {
+            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 {
+                    inner.set_compare(n, at as u16);
+                    // NOTE(unsafe) We're in a critical section
+                    unsafe {
+                        inner.set_compare_interrupt(n, true);
+                    }
+                }
+            }
+        })
+    }
+
+    fn trigger_alarm(&self, n: usize, cs: CriticalSection) {
+        let inner = T::inner();
+        // NOTE(unsafe) We have a critical section
+        unsafe {
+            inner.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 ()) {
+        critical_section::with(|cs| {
+            let alarm = &self.alarms.borrow(cs)[n - 1];
+            alarm.callback.set(Some((callback, ctx)));
+        })
+    }
+
+    fn set_alarm(&self, n: usize, timestamp: u64) {
+        critical_section::with(|cs| {
+            let inner = T::inner();
+
+            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);
+                inner.set_compare(n, safe_timestamp as u16);
+
+                // NOTE(unsafe) We're in a critical section
+                unsafe {
+                    inner.set_compare_interrupt(n, true);
+                }
+            } else {
+                unsafe {
+                    inner.set_compare_interrupt(n, false);
+                }
+            }
+        })
+    }
+
+    pub fn alarm1(&'static self) -> Alarm<T> {
+        Alarm { n: 1, rtc: self }
+    }
+    pub fn alarm2(&'static self) -> Alarm<T> {
+        Alarm { n: 2, rtc: self }
+    }
+    pub fn alarm3(&'static self) -> Alarm<T> {
+        Alarm { n: 3, rtc: self }
+    }
+}
+
+impl<T: Instance> embassy::time::Clock for RTC<T> {
+    fn now(&self) -> u64 {
+        let inner = T::inner();
+
+        let period = self.period.load(Ordering::Relaxed);
+        compiler_fence(Ordering::Acquire);
+        let counter = inner.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);
+    }
+}
+
+pub struct TimerInner(pub(crate) TimGp16);
+
+impl TimerInner {
+    unsafe fn prepare(&self, pfreq: Hertz, ppre: u8) {
+        self.stop_and_reset();
+
+        let multiplier = if ppre == 1 { 1 } else { 2 };
+        let freq = pfreq.0 * multiplier;
+        let psc = freq / TICKS_PER_SECOND as u32 - 1;
+        let psc: u16 = psc.try_into().unwrap();
+
+        self.set_psc_arr(psc, u16::MAX);
+        // Mid-way point
+        self.set_compare(0, 0x8000);
+        self.set_compare_interrupt(0, true);
+    }
+
+    unsafe fn start_counter(&self) {
+        self.0.cr1().modify(|w| w.set_cen(true));
+    }
+
+    unsafe fn stop_and_reset(&self) {
+        let regs = self.0;
+
+        regs.cr1().modify(|w| w.set_cen(false));
+        regs.cnt().write(|w| w.set_cnt(0));
+    }
+
+    fn overflow_interrupt_status(&self) -> bool {
+        // NOTE(unsafe) Atomic read with no side-effects
+        unsafe { self.0.sr().read().uif() }
+    }
+
+    unsafe fn overflow_clear_flag(&self) {
+        self.0.sr().modify(|w| w.set_uif(false));
+    }
+
+    unsafe fn set_psc_arr(&self, psc: u16, arr: u16) {
+        use crate::pac::timer::vals::Urs;
+
+        let regs = self.0;
+
+        regs.psc().write(|w| w.set_psc(psc));
+        regs.arr().write(|w| w.set_arr(arr));
+
+        // Set URS, generate update and clear URS
+        regs.cr1().modify(|w| w.set_urs(Urs::COUNTERONLY));
+        regs.egr().write(|w| w.set_ug(true));
+        regs.cr1().modify(|w| w.set_urs(Urs::ANYEVENT));
+    }
+
+    fn compare_interrupt_status(&self, n: usize) -> bool {
+        if n > 3 {
+            false
+        } else {
+            // NOTE(unsafe) Atomic read with no side-effects
+            unsafe { self.0.sr().read().ccif(n) }
+        }
+    }
+
+    unsafe fn compare_clear_flag(&self, n: usize) {
+        if n > 3 {
+            return;
+        }
+        self.0.sr().modify(|w| w.set_ccif(n, false));
+    }
+
+    fn set_compare(&self, n: usize, value: u16) {
+        if n > 3 {
+            return;
+        }
+        // NOTE(unsafe) Atomic write
+        unsafe {
+            self.0.ccr(n).write(|w| w.set_ccr(value));
+        }
+    }
+
+    unsafe fn set_compare_interrupt(&self, n: usize, enable: bool) {
+        if n > 3 {
+            return;
+        }
+        self.0.dier().modify(|w| w.set_ccie(n, enable));
+    }
+
+    fn counter(&self) -> u16 {
+        // NOTE(unsafe) Atomic read with no side-effects
+        unsafe { self.0.cnt().read().cnt() }
+    }
+}
+
+// ------------------------------------------------------
+
+pub(crate) mod sealed {
+    use super::*;
+    pub trait Instance {
+        type Interrupt: Interrupt;
+
+        fn inner() -> TimerInner;
+        fn state() -> &'static AtomicWaker;
+    }
+}
+
+pub trait Instance: sealed::Instance + Sized + 'static {}
+
+/*
+
+#[allow(unused_macros)]
+macro_rules! impl_timer {
+    ($module:ident: ($TYPE:ident, $INT:ident, $apbenr:ident, $enrbit:expr, $apbrstr:ident, $rstrbit:expr, $ppre:ident, $pclk: ident), 3) => {
+        mod $module {
+            use super::*;
+
+            impl sealed::Instance for $TYPE {}
+
+            impl Instance for $TYPE {
+                type Interrupt = interrupt::$INT;
+
+                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.$ppre()
+                }
+
+                fn pclk(clocks: &Clocks) -> u32 {
+                    clocks.$pclk().0
+                }
+            }
+        }
+    };
+
+    ($module:ident: ($TYPE:ident, $INT:ident, $apbenr:ident, $enrbit:expr, $apbrstr:ident, $rstrbit:expr, $ppre:ident, $pclk: ident), 1) => {
+        mod $module {
+            use super::*;
+            use crate::hal::pac::{$TYPE, RCC};
+
+            impl sealed::Sealed for $TYPE {}
+
+            impl Instance for $TYPE {
+                type Interrupt = interrupt::$INT;
+                const REAL_ALARM_COUNT: usize = 1;
+
+                fn enable_clock(&self) {
+                    // NOTE(unsafe) It will only be used for atomic operations
+                    unsafe {
+                        let rcc = &*RCC::ptr();
+
+                        bb::set(&rcc.$apbenr, $enrbit);
+                        bb::set(&rcc.$apbrstr, $rstrbit);
+                        bb::clear(&rcc.$apbrstr, $rstrbit);
+                    }
+                }
+
+                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()) }),
+                        _ => {}
+                    }
+                }
+
+                fn set_compare_interrupt(&self, n: usize, enable: bool) {
+                    if n > 1 {
+                        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(),
+                        _ => false,
+                    }
+                }
+
+                fn compare_clear_flag(&self, n: usize) {
+                    if n > 1 {
+                        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.$ppre()
+                }
+
+                fn pclk(clocks: &Clocks) -> u32 {
+                    clocks.$pclk().0
+                }
+            }
+        }
+    };
+}
+*/
+
+/*
+impl_timer!(tim2: (TIM2, TIM2, apb1enr, 0, apb1rstr, 0, ppre1, pclk1), 3);
+
+impl_timer!(tim3: (TIM3, TIM3, apb1enr, 1, apb1rstr, 1, ppre1, pclk1), 3);
+
+
+impl_timer!(tim4: (TIM4, TIM4, apb1enr, 2, apb1rstr, 2, ppre1, pclk1), 3);
+
+impl_timer!(tim5: (TIM5, TIM5, apb1enr, 3, apb1rstr, 3, ppre1, pclk1), 3);
+
+impl_timer!(tim9: (TIM9, TIM1_BRK_TIM9, apb2enr, 16, apb2rstr, 16, ppre2, pclk2), 1);
+
+#[cfg(not(any(feature = "stm32f401", feature = "stm32f410", feature = "stm32f411")))]
+impl_timer!(tim12: (TIM12, TIM8_BRK_TIM12, apb1enr, 6, apb1rstr, 6, ppre1, pclk1), 1);
+*/