Add Timer 'read()' and TICKS_PER_SECOND.

Author: Jonathan Pallant (42 Technology)

nrf52-hal-common/src/timer.rs

@@ -22,12 +22,17 @@ use crate::target::{TIMER3, TIMER4};
 ///
 /// Right now, this is a very basic interface. The timer will always be
 /// hardcoded to a frequency of 1 MHz and 32 bits accuracy.
+///
+/// CC[0] is used for the current/most-recent delay period and CC[1] is used
+/// to grab the current value of the counter at a given instant.
 pub struct Timer<T>(T);
 
 impl<T> Timer<T>
 where
     T: Instance,
 {
+    pub const TICKS_PER_SECOND: u32 = 1_000_000;
+
     pub fn new(timer: T) -> Self {
         timer
             .shorts
@@ -45,6 +50,12 @@ where
         self.0
     }
 
+    /// Return the current value of the counter, by capturing to CC[1].
+    pub fn read(&self) -> u32 {
+        self.0.tasks_capture[1].write(|w| w.tasks_capture().trigger());
+        self.0.cc[1].read().bits()
+    }
+
     /// Enables the interrupt for this timer
     ///
     /// Enables an interrupt that is fired when the timer reaches the value that