Add SYSTIMER based ESP32-C3 monotonic (#972)

* add esp32c3 monotonic

* fix tests

1 files changed, 193 insertions, 0 deletions

diff --git a/rtic-monotonics/src/esp32c3.rs b/rtic-monotonics/src/esp32c3.rs
new file mode 100644
index 0000000..61e044e
--- /dev/null
+++ b/rtic-monotonics/src/esp32c3.rs
@@ -0,0 +1,193 @@
+//! [`Monotonic`](rtic_time::Monotonic) implementation for ESP32C3's SYSTIMER.
+//!
+//! Always runs at a fixed rate of 16 MHz.
+//!
+//! # Example
+//!
+//! ```
+//! use rtic_monotonics::esp32c3::prelude::*;
+//!
+//! esp32c3_systimer_monotonic!(Mono);
+//!
+//! fn init() {
+//!     # // This is normally provided by the selected PAC
+//!     # let timer = unsafe { esp32c3::Peripherals::steal() }.SYSTIMER;
+//!     #
+//!     // Start the monotonic
+//!     Mono::start(timer);
+//! }
+//!
+//! async fn usage() {
+//!     loop {
+//!          // Use the monotonic
+//!          let timestamp = Mono::now();
+//!          Mono::delay(100.millis()).await;
+//!     }
+//! }
+//! ```
+
+/// Common definitions and traits for using the RP2040 timer monotonic
+pub mod prelude {
+    pub use crate::esp32c3_systimer_monotonic;
+
+    pub use crate::Monotonic;
+
+    pub use fugit::{self, ExtU64, ExtU64Ceil};
+}
+use crate::TimerQueueBackend;
+use esp32c3::{INTERRUPT_CORE0, SYSTIMER};
+use rtic_time::timer_queue::TimerQueue;
+
+/// Timer implementing [`TimerQueueBackend`].
+pub struct TimerBackend;
+
+impl TimerBackend {
+    /// Starts the monotonic timer.
+    ///
+    /// **Do not use this function directly.**
+    ///
+    /// Use the prelude macros instead.
+    pub fn _start(timer: SYSTIMER) {
+        const INTERRUPT_MAP_BASE: u32 = 0x600c2000;
+        let interrupt_number = 37 as isize;
+        let cpu_interrupt_number = 31 as isize;
+        unsafe {
+            let intr_map_base = INTERRUPT_MAP_BASE as *mut u32;
+            intr_map_base
+                .offset(interrupt_number)
+                .write_volatile(cpu_interrupt_number as u32);
+            //map peripheral interrupt to CPU interrupt
+            (*INTERRUPT_CORE0::ptr())
+                .cpu_int_enable()
+                .modify(|r, w| w.bits((1 << cpu_interrupt_number) | r.bits())); //enable the CPU interupt.
+            let intr = INTERRUPT_CORE0::ptr();
+            let intr_prio_base = (*intr).cpu_int_pri_0().as_ptr();
+
+            intr_prio_base
+                .offset(cpu_interrupt_number)
+                .write_volatile(15 as u32);
+        }
+        timer.conf().write(|w| w.timer_unit0_work_en().set_bit());
+        timer
+            .conf()
+            .write(|w| w.timer_unit1_core0_stall_en().clear_bit());
+        TIMER_QUEUE.initialize(Self {})
+    }
+}
+
+static TIMER_QUEUE: TimerQueue<TimerBackend> = TimerQueue::new();
+use esp32c3;
+impl TimerQueueBackend for TimerBackend {
+    type Ticks = u64;
+    fn now() -> Self::Ticks {
+        let peripherals = unsafe { esp32c3::Peripherals::steal() };
+        peripherals
+            .SYSTIMER
+            .unit0_op()
+            .write(|w| w.timer_unit0_update().set_bit());
+        // this must be polled until value is valid
+        while {
+            peripherals
+                .SYSTIMER
+                .unit0_op()
+                .read()
+                .timer_unit0_value_valid()
+                == false
+        } {}
+        let instant: u64 = (peripherals.SYSTIMER.unit0_value_lo().read().bits() as u64)
+            | ((peripherals.SYSTIMER.unit0_value_hi().read().bits() as u64) << 32);
+        instant
+    }
+
+    fn set_compare(instant: Self::Ticks) {
+        let systimer = unsafe { esp32c3::Peripherals::steal() }.SYSTIMER;
+        systimer
+            .target0_conf()
+            .write(|w| w.target0_timer_unit_sel().set_bit());
+        systimer
+            .target0_conf()
+            .write(|w| w.target0_period_mode().clear_bit());
+        systimer
+            .target0_lo()
+            .write(|w| unsafe { w.bits((instant & 0xFFFFFFFF).try_into().unwrap()) });
+        systimer
+            .target0_hi()
+            .write(|w| unsafe { w.bits((instant >> 32).try_into().unwrap()) });
+        systimer
+            .comp0_load()
+            .write(|w| w.timer_comp0_load().set_bit()); //sync period to comp register
+        systimer.conf().write(|w| w.target0_work_en().set_bit());
+        systimer.int_ena().write(|w| w.target0().set_bit());
+    }
+
+    fn clear_compare_flag() {
+        unsafe { esp32c3::Peripherals::steal() }
+            .SYSTIMER
+            .int_clr()
+            .write(|w| w.target0().bit(true));
+    }
+
+    fn pend_interrupt() {
+        extern "C" {
+            fn cpu_int_31_handler();
+        }
+        //run the timer interrupt handler in a critical section to emulate a max priority
+        //interrupt.
+        //since there is no hardware support for pending a timer interrupt.
+        riscv::interrupt::disable();
+        unsafe { cpu_int_31_handler() };
+        unsafe { riscv::interrupt::enable() };
+    }
+
+    fn timer_queue() -> &'static TimerQueue<Self> {
+        &TIMER_QUEUE
+    }
+}
+
+/// Create an ESP32-C3 SysTimer based monotonic and register the necessary interrupt for it.
+///
+/// See [`crate::esp32c3`] for more details.
+///
+/// # Arguments
+///
+/// * `name` - The name that the monotonic type will have.
+#[macro_export]
+macro_rules! esp32c3_systimer_monotonic {
+    ($name:ident) => {
+        /// A `Monotonic` based on the ESP32-C3 SysTimer peripheral.
+        pub struct $name;
+
+        impl $name {
+            /// Starts the `Monotonic`.
+            ///
+            /// This method must be called only once.
+            pub fn start(timer: esp32c3::SYSTIMER) {
+                #[export_name = "cpu_int_31_handler"]
+                #[allow(non_snake_case)]
+                unsafe extern "C" fn Systimer() {
+                    use $crate::TimerQueueBackend;
+                    $crate::esp32c3::TimerBackend::timer_queue().on_monotonic_interrupt();
+                }
+
+                $crate::esp32c3::TimerBackend::_start(timer);
+            }
+        }
+
+        impl $crate::TimerQueueBasedMonotonic for $name {
+            type Backend = $crate::esp32c3::TimerBackend;
+            type Instant = $crate::fugit::Instant<
+                <Self::Backend as $crate::TimerQueueBackend>::Ticks,
+                1,
+                16_000_000,
+            >;
+            type Duration = $crate::fugit::Duration<
+                <Self::Backend as $crate::TimerQueueBackend>::Ticks,
+                1,
+                16_000_000,
+            >;
+        }
+
+        $crate::rtic_time::impl_embedded_hal_delay_fugit!($name);
+        $crate::rtic_time::impl_embedded_hal_async_delay_fugit!($name);
+    };
+}