Provide a delay driver based on SysTick

CHANGELOG.md

@@ -13,6 +13,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
   various NVIC functions, replacing the previous use of `Nr` from bare-metal.
 - Associated const `PTR` is introduced to Core Peripherals to
   eventually replace the existing `ptr()` API.
+- A delay driver based on SysTick.
 
 ## [v0.6.2] - 2020-01-12
 

Cargo.toml

@@ -19,6 +19,7 @@ links = "cortex-m"  # prevent multiple versions of this crate to be linked toget
 bare-metal = { version = "0.2.0", features = ["const-fn"] }
 volatile-register = "0.2.0"
 bitfield = "0.13.2"
+embedded-hal = "0.2.4"
 
 [package.metadata.docs.rs]
 targets = [

src/delay.rs

@@ -0,0 +1,119 @@
+//! A delay driver based on SysTick
+
+use crate::peripheral::{syst::SystClkSource, SYST};
+use embedded_hal::blocking::delay::{DelayMs, DelayUs};
+
+/// System timer (SysTick) as a delay provider
+pub struct Delay {
+    syst: SYST,
+    ahb_frequency: u32,
+}
+
+impl Delay {
+    /// Configures the system timer (SysTick) as a delay provider
+    ///
+    /// `ahb_frequency` is a frequency of the AHB bus in Hz
+    #[inline]
+    pub fn new(mut syst: SYST, ahb_frequency: u32) -> Self {
+        syst.set_clock_source(SystClkSource::Core);
+
+        Delay { syst, ahb_frequency }
+    }
+
+    /// Releases the system timer (SysTick) resource
+    #[inline]
+    pub fn free(self) -> SYST {
+        self.syst
+    }
+
+    fn _delay_us(&mut self, us: u32) {
+        let ticks = (us as u64) * (self.ahb_frequency as u64) / 1_000_000;
+
+        let full_cycles = ticks >> 24;
+        if full_cycles > 0 {
+            self.syst.set_reload(0xffffff);
+            self.syst.clear_current();
+            self.syst.enable_counter();
+
+            for _ in 0..full_cycles {
+                while !self.syst.has_wrapped() {}
+            }
+        }
+
+        let ticks = (ticks & 0xffffff) as u32;
+        if ticks > 1 {
+            self.syst.set_reload(ticks - 1);
+            self.syst.clear_current();
+            self.syst.enable_counter();
+
+            while !self.syst.has_wrapped() {}
+        }
+
+        self.syst.disable_counter();
+    }
+}
+
+impl DelayMs<u32> for Delay {
+    #[inline]
+    fn delay_ms(&mut self, mut ms: u32) {
+        // 4294967 is the highest u32 value which you can multiply by 1000 without overflow
+        while ms > 4294967 {
+            self.delay_us(4294967000u32);
+            ms -= 4294967;
+        }
+        self.delay_us(ms * 1_000);
+    }
+}
+
+// This is a workaround to allow `delay_ms(42)` construction without specifying a type.
+impl DelayMs<i32> for Delay {
+    #[inline(always)]
+    fn delay_ms(&mut self, ms: i32) {
+        assert!(ms >= 0);
+        self.delay_ms(ms as u32);
+    }
+}
+
+impl DelayMs<u16> for Delay {
+    #[inline(always)]
+    fn delay_ms(&mut self, ms: u16) {
+        self.delay_ms(u32::from(ms));
+    }
+}
+
+impl DelayMs<u8> for Delay {
+    #[inline(always)]
+    fn delay_ms(&mut self, ms: u8) {
+        self.delay_ms(u32::from(ms));
+    }
+}
+
+impl DelayUs<u32> for Delay {
+    #[inline]
+    fn delay_us(&mut self, us: u32) {
+        self._delay_us(us);
+    }
+}
+
+// This is a workaround to allow `delay_us(42)` construction without specifying a type.
+impl DelayUs<i32> for Delay {
+    #[inline(always)]
+    fn delay_us(&mut self, us: i32) {
+        assert!(us >= 0);
+        self.delay_us(us as u32);
+    }
+}
+
+impl DelayUs<u16> for Delay {
+    #[inline(always)]
+    fn delay_us(&mut self, us: u16) {
+        self.delay_us(u32::from(us))
+    }
+}
+
+impl DelayUs<u8> for Delay {
+    #[inline(always)]
+    fn delay_us(&mut self, us: u8) {
+        self.delay_us(u32::from(us))
+    }
+}

src/lib.rs

@@ -61,6 +61,7 @@ mod macros;
 pub mod asm;
 #[cfg(armv8m)]
 pub mod cmse;
+pub mod delay;
 pub mod interrupt;
 #[cfg(all(not(armv6m), not(armv8m_base)))]
 pub mod itm;