fix stopwatch

Author: dotcypress

examples/stopwatch.rs

@@ -31,7 +31,7 @@ fn main() -> ! {
     #[cfg(feature = "stm32g0x0")]
     let mut stopwatch = dp.TIM3.stopwatch(&mut rcc);
 
-    stopwatch.set_prescaler(1);
+    stopwatch.set_prescaler(0);
 
     let elapsed_us = stopwatch.trace(|| {
         delay.delay(100.us());

src/timer/stopwatch.rs

@@ -71,7 +71,7 @@ macro_rules! stopwatches {
                 pub fn elapsed(&self, ts: Instant) -> MicroSecond {
                     let now = self.now().0;
                     let cycles = now.wrapping_sub(ts.0);
-                    self.clk.duration(cycles << self.tim.psc.read().bits())
+                    self.clk.duration(cycles * (1 + self.tim.psc.read().bits()))
                 }
 
                 pub fn trace<F>(&self, mut closure: F) -> MicroSecond
@@ -81,7 +81,7 @@ macro_rules! stopwatches {
                     let started = self.now().0;
                     closure();
                     let now = self.now().0;
-                    self.clk.duration(now.wrapping_sub(started) << self.tim.psc.read().bits())
+                    self.clk.duration(now.wrapping_sub(started) * (1 + self.tim.psc.read().bits()))
                 }
             }