Ultra Low Power Timers

There are 3 ULP timers in the Dolphin system as shown in the table below.

TimerName	TimerEnum	Clock Source	Width	Minimum-period (One-tick)	Maximum-period	Typical uncalibrated error	Description of the timer and usage
Watchdog Timer	WATCHDOG_TIMER	100Hz intern WRCO	24 bit	10 ms	16 777 215 = 46.6 hours	40%	This timer always runs (can't be disabled). A counter underflow causes a WatchdogReset in any Sleep Modes (or in CPU mode). The counter counts down.
Flywheel Timer	FLYWHEEL_TIMER	32.768 kHz extern Wristwatch XTAL (WXTAL)	24 bit	~1 ms (1/1024s)	16 777 215 = ~4.6 hours	delta fWXO, ca. 0.01%	Can be enabled/disabled. Needs an external wrist-watch XTAL and the #WXID_IO and #WXOD_IO pins configured as WXTAL (DolphinV4 API Configurator). If enabled and CPU is in sleep (pwr_timerSleep), a counter overflow results in a FlywheelReset. The counter counts up.
ShortTerm Timer	SHORT_TERM_TIMER	100kHz intern SRCO	16 bit	10 us	65 535 = 0.6 seconds	35%	Can be enabled/disabled. If enabled and CPU is in sleep (pwr_timerSleep), a counter overflow results in a CPU wake-up. The CPU will continue the program execution. The counter counts down.

All the ultra low power timers can be used

• In sleep_mode to wakeup at predefined time
  
• In cpu_mode to measure time by using the functions pwr_getSleepTimerCounter, pwr_resetSleepTimer, pwr_getSleepTimerStatus

Note:

Upon a PowerOnReset, PinReset the ULP timers are put to initial state. This is the following:

• Watchdog period is set to 0xFFFFFF and enable
• Flywheel timer is disabled
• ShortTerm timer is disabled

Each timer has a certain error (see References Dolphin User Manual). To reduce this error the timers are calibrated during module production. For further information please. read Calibration of the timers

The Flywheel wristwatch crystal clock frequency (see the recommended type in the data sheet) is 32.768 kHz. Thus 1 Flywheel period is not exactly 1ms but 1/1024s = 0,9765625ms. That's why all the time informations in this manual are for the flywheel timer showed as an approximate value with ~. Using the calibration value from the configuration area this error can be corrected.