hwtimer: Tidy up and clarify some hw_clock comments
From what I can tell the counter has to tick over at the rate of 1MHz.
Update the comments to make that clear.
BRANCH=none
TEST= make buildall -j50
/**
* Programs when the next timer should fire an interrupt.
- * deadline: timestamp of the event.
+ *
+ * The deadline is ahead of the current counter (which may of course wrap) by
+ * the number of microseconds until the interrupt should fire.
+ *
+ * @param deadline timestamp of the event in microseconds
*/
void __hw_clock_event_set(uint32_t deadline);
@@ -20,10 +24,23 @@ uint32_t __hw_clock_event_get(void);
/* Cancel the next event programed by __hw_clock_event_set */
void __hw_clock_event_clear(void);
-/* Returns the value of the free-running counter used as clock. */
+/**
+ * Get the value of the free-running counter used as clock
+ *
+ * The counter resolution must be 1us, since udelay() relies on this.
+ *
+ * @return current counter value
+ */
uint32_t __hw_clock_source_read(void);
-/* Override the current value of the hardware counter */
+/**
+ * Override the current value of the hardware counter
+ *
+ * The new value takes effect immediately and the counter continues counting
+ * from there, assuming it is enabled
+ *
+ * @ts Value to write
+ */
void __hw_clock_source_set(uint32_t ts);
/**
