irq: Support sleeping when mcu is idle

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/sam3x8e/timer.c

@@ -18,6 +18,13 @@ timer_set(uint32_t value)
     TC0->TC_CHANNEL[0].TC_RA = value;
 }
 
+// Return the next scheduled wake up time
+uint32_t
+timer_get_next(void)
+{
+    return TC0->TC_CHANNEL[0].TC_RA;
+}
+
 // Return the current time (in absolute clock ticks).
 uint32_t
 timer_read_time(void)