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Clocks

Timers and their capabilities can vary considerably. For example, Timer1 can be configured with a prescaler of 1, 16 or 256 which affects both the resolution and range of the timer. One might also consider the CPU cycle counter to have a selectable prescaler of 1 or 2, depending on whether it's running at 80MHz or 160MHz.

A :cpp:class:`Clock <NanoTime::Clock>` definition is a class template which allows us to query timer properties and perform time conversions for a specific timer configuration. These definitions can be found in :source:`Sming/Platform/Clocks.h`.

Note

A Clock is a purely virtual construct and does not provide any means to configure the hardware, although it does provide the :cpp:func:`ticks() <Clock::ticks>` method to obtain the current timer value.

Clocks are made more useful by :cpp:class:`TimeSource <NanoTime::TimeSource>`, a generic class template defined in :source:`Sming/Core/NanoTime.h`. This provides methods to convert between time values and tick values for a specific time unit.

Let's say we want a microsecond source using Timer2:

TimeSource<Timer2Clock, NanoTime::Microseconds, uint32_t> t2source;

We can now call methods of t2source like this:

// What's the maximum Timer2 value in microseconds?
Serial.println(t2source.maxClockTime());

// How many clock ticks per microsecond ?
Serial.println(t2source.ticksPerUnit()); // 5/1

// How many clock ticks for 100us ?
Serial.println(t2source.template timeConst<100>().ticks());

Note that all of these values are computed at compile time. Some runtime conversions:

Serial.println(t2source.timeToTicks(100));
Serial.println(t2source.ticksToTime(10000));

The results of conversions are rounded rather than truncated, which provides more accurate results and reduces timing jitter.

For debugging purposes you can print a description:

Serial.println(t2source.toString()); // "Timer2Clock/5MHz/32-bit/microseconds"

See :source:`Sming/Core/NanoTime.h` for further details.

System Clock API

.. doxygengroup:: system_clocks
   :content-only:
   :members: