modm API documentation
Classes
Cycle Counter
External Device Drivers

Classes

class  modm::CycleCounter
 

Detailed Description

lbuild module: modm:driver:cycle_counter

Allows you to measure time with cycle accuracy on AVR and ARM devices. This module wraps common functionality around different timers:

// place counter in the fastest memory to limit sampling overhead
modm_fastdata modm::CycleCounter counter;
// initialize once before sampling
counter.initialize();
// Sample the timer now
counter.start();
// perform your operation and then sample again
counter.stop();
// you can now get cycles or milli-/micro-/nanoseconds
counter.cycles();
counter.nanoseconds();
counter.microseconds();
counter.milliseconds();
Note
AVR TC1 Limitations The 16-bit timer limits the maximum measurable time to just 4ms at 16MHz!
Cortex-M0 SysTick Limitations The ARMv6-M architecture does not come with a free running counter, therefore this class uses the SysTick timer. However, the timer is already used by the modm:platform:systick module to provide modm::Clock, which limits the maximum measurable time to just 1ms! The systick may also be run with a /8 prescaler, which this class compensates for but this still reduces sampling resolution to 8 cycles!

In case these limitations are not acceptable, you may force initialize the SysTick, which will break modm::Clock functionality in favor of accurate measurements. You may of course reinitialize the SysTick after your measurement to regain modm::Clock functionality! However, the software timers of the modm:processing:timer module may not work correctly anymore and may need to be reinitialized.

~~~{.cpp} Always initializes the SysTick for modm::Clock Board::initialize();

but we need an accurate cycle counter counter.initialize(/*force=