Increase SysTick delay limit

Leverage a full 32 bit range instead of only 24 bit range.
This will increase the maximum possible delay from ~2 seconds
up to 9 minutes.

Also cap the value, instead of panicking, if the value is to high.

Fixes #203

Author: Sh3Rm4n

CHANGELOG.md

@@ -9,7 +9,12 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Changed
 
-- Added support for more CAN bit rates and modes. ([#186](https://github.com/stm32-rs/stm32f3xx-hal/pull/186)
+- Added support for more CAN bit rates and modes. ([#186])
+
+### Fixed
+
+- Delay based on systick no longer panics ([#203]) for to high values
+  and support longer delays ([#208])
 
 ## [v0.6.1] - 2020-12-10
 
@@ -266,6 +271,9 @@ let clocks = rcc
 
 - Support `stm32f303` device
 
+[#208]: https://github.com/stm32-rs/stm32f3xx-hal/pull/208
+[#203]: https://github.com/stm32-rs/stm32f3xx-hal/issues/203
+[#186]: https://github.com/stm32-rs/stm32f3xx-hal/pull/186
 [#184]: https://github.com/stm32-rs/stm32f3xx-hal/pull/184
 [#172]: https://github.com/stm32-rs/stm32f3xx-hal/pull/172
 [#170]: https://github.com/stm32-rs/stm32f3xx-hal/pull/170

src/delay.rs

@@ -16,6 +16,15 @@ pub struct Delay {
 
 impl Delay {
     /// Configures the system timer (SysTick) as a delay provider
+    ///
+    /// # Limitations
+    ///
+    /// Depending on the core clock, this delay provider
+    /// can delay between 1 minute (for 72 Mhz) up to almost 9 minutes (for 8 Mhz).
+    /// Higher input values will be capped to these limits.
+    ///
+    /// For accuracy purposes and because this is a blocking, busy-waiting function,
+    /// if delays in the second to minute range are needed, use timers instead.
     pub fn new(mut syst: SYST, clocks: Clocks) -> Self {
         syst.set_clock_source(SystClkSource::Core);
 
@@ -30,7 +39,7 @@ impl Delay {
 
 impl DelayMs<u32> for Delay {
     fn delay_ms(&mut self, ms: u32) {
-        self.delay_us(ms * 1_000);
+        self.delay_us(ms.saturating_mul(1_000));
     }
 }
 
@@ -48,17 +57,36 @@ impl DelayMs<u8> for Delay {
 
 impl DelayUs<u32> for Delay {
     fn delay_us(&mut self, us: u32) {
-        let rvr = us * (self.clocks.sysclk().0 / 1_000_000);
-
-        crate::assert!(rvr < (1 << 24));
-
-        self.syst.set_reload(rvr);
-        self.syst.clear_current();
-        self.syst.enable_counter();
-
-        while !self.syst.has_wrapped() {}
-
-        self.syst.disable_counter();
+        // The RVR register is 24 bits wide, as SysTick is based on a 24 bit counter
+        const MAX_RVR: u32 = 1 << 24;
+
+        // Depending on hclk (core clock), this 32 bit value allows
+        // delays between 1 min to 9 min.
+        //
+        // (((32^2) - 1) / 72) µs ~ 59.6 seconds
+        // (((32^2) - 1) / 8) µs  ~ 536.8 seconds
+        let mut total_rvr = us.saturating_mul(self.clocks.hclk().0 / 1_000_000);
+
+        // Use the full 32 bit range to allow longer delays
+        //
+        // Like dividing total_rvr / MAX_RVR
+        // and delaying by MAX_RVR * (fraction).
+        while total_rvr != 0 {
+            let current_rvr = if total_rvr < MAX_RVR {
+                total_rvr
+            } else {
+                MAX_RVR
+            };
+            total_rvr -= current_rvr;
+
+            self.syst.set_reload(current_rvr);
+            self.syst.clear_current();
+            self.syst.enable_counter();
+
+            while !self.syst.has_wrapped() {}
+
+            self.syst.disable_counter();
+        }
     }
 }