Merge pull request #12326 from kjbracey-arm/systimer_abs_fix

Correct SysTimer absolute time calculations

Author: kjbracey

platform/source/SysTimer.cpp

@@ -52,7 +52,8 @@ SysTimer<US_IN_TICK, IRQ>::SysTimer() :
 #else
     TimerEvent(get_us_ticker_data()),
 #endif
-    _time_us(ticker_read_us(_ticker_data)),
+    _epoch(ticker_read_us(_ticker_data)),
+    _time_us(_epoch),
     _tick(0),
     _unacknowledged_ticks(0),
     _wake_time_set(false),
@@ -66,7 +67,8 @@ SysTimer<US_IN_TICK, IRQ>::SysTimer() :
 template<uint32_t US_IN_TICK, bool IRQ>
 SysTimer<US_IN_TICK, IRQ>::SysTimer(const ticker_data_t *data) :
     TimerEvent(data),
-    _time_us(ticker_read_us(_ticker_data)),
+    _epoch(ticker_read_us(_ticker_data)),
+    _time_us(_epoch),
     _tick(0),
     _unacknowledged_ticks(0),
     _wake_time_set(false),
@@ -104,7 +106,7 @@ void SysTimer<US_IN_TICK, IRQ>::set_wake_time(uint64_t at)
     }
 
     uint64_t ticks_to_sleep = at - _tick;
-    uint64_t wake_time = at * US_IN_TICK;
+    uint64_t wake_time = _epoch + at * US_IN_TICK;
 
     /* Set this first, before attaching the interrupt that can unset it */
     _wake_time_set = true;

platform/source/SysTimer.h

@@ -225,6 +225,7 @@ class SysTimer: private mbed::TimerEvent, private mbed::NonCopyable<SysTimer<US_
     uint64_t _elapsed_ticks() const;
     static void _set_irq_pending();
     static void _clear_irq_pending();
+    const us_timestamp_t _epoch;
     us_timestamp_t _time_us;
     uint64_t _tick;
     uint8_t _unacknowledged_ticks;