pw::chrono::SystemClock Struct Reference

#include <system_clock.h>

Public Types
using	rep = int64_t
using	period = std::ratio< PW_CHRONO_SYSTEM_CLOCK_PERIOD_SECONDS_NUMERATOR, PW_CHRONO_SYSTEM_CLOCK_PERIOD_SECONDS_DENOMINATOR >
	The period must be provided by the backend.
using	duration = std::chrono::duration< rep, period >
	Alias for durations representable with this clock.
using	time_point = std::chrono::time_point< SystemClock >

Static Public Member Functions
static time_point	now () noexcept
	This is thread and IRQ safe. This must be provided by the backend.
template<class Rep , class Period >
static constexpr duration	for_at_least (std::chrono::duration< Rep, Period > d)
static time_point	TimePointAfterAtLeast (duration after_at_least)

Static Public Attributes
static constexpr Epoch	epoch = backend::kSystemClockEpoch
	The epoch must be provided by the backend.
static constexpr bool	is_monotonic = true
static constexpr bool	is_steady = false
static constexpr bool	is_free_running = backend::kSystemClockFreeRunning
static constexpr bool	is_stopped_in_halting_debug_mode = true
	The clock must stop while in halting debug mode.
static constexpr bool	is_always_enabled = true
	The now() function can be invoked at any time.
static constexpr bool	is_nmi_safe = backend::kSystemClockNmiSafe

Detailed Description

The SystemClock represents an unsteady, monotonic clock.

The epoch of this clock is unspecified and may not be related to wall time (for example, it can be time since boot). The time between ticks of this clock may vary due to sleep modes and potential interrupt handling. SystemClock meets the requirements of C++'s TrivialClock and Pigweed's PigweedClock.

SystemClock is compatible with C++'s Clock & TrivialClock including:

• SystemClock::rep
• SystemClock::period
• SystemClock::duration
• SystemClock::time_point
• SystemClock::is_steady
• SystemClock::now()

Example:

SystemClock::time_point before = SystemClock::now();
TakesALongTime();
SystemClock::duration time_taken = SystemClock::now() - before;
bool took_way_too_long = false;
if (time_taken > std::chrono::seconds(42)) {
  took_way_too_long = true;
}

This code is thread & IRQ safe, it may be NMI safe depending on is_nmi_safe.

Member Function Documentation

for_at_least()

template<class Rep , class Period >

static constexpr duration pw::chrono::SystemClock::for_at_least ( std::chrono::duration< Rep, Period >  d )

inlinestaticconstexpr

This is purely a helper, identical to directly using std::chrono::ceil, to convert a duration type which cannot be implicitly converted where the result is rounded up.

TimePointAfterAtLeast()

static time_point pw::chrono::SystemClock::TimePointAfterAtLeast ( duration  after_at_least )

inlinestatic

Computes the nearest time_point after the specified duration has elapsed.

This is useful for translating delay or timeout durations into deadlines.

The time_point is computed based on now() plus the specified duration where a singular clock tick is added to handle partial ticks. This ensures that a duration of at least 1 tick does not result in [0,1] ticks and instead in [1,2] ticks.

Member Data Documentation

is_free_running

constexpr bool pw::chrono::SystemClock::is_free_running = backend::kSystemClockFreeRunning

staticconstexpr

The now() function may not move forward while in a critical section or interrupt. This must be provided by the backend.

is_monotonic

constexpr bool pw::chrono::SystemClock::is_monotonic = true

staticconstexpr

The time points of this clock cannot decrease, however the time between ticks of this clock may slightly vary due to sleep modes. The duration during sleep may be ignored or backfilled with another clock.

is_nmi_safe

constexpr bool pw::chrono::SystemClock::is_nmi_safe = backend::kSystemClockNmiSafe

staticconstexpr

The now() function may work in non-maskable interrupt contexts (e.g. exception/fault handlers), depending on the backend. This must be provided by the backend.

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The documentation for this struct was generated from the following file:

• /b/s/w/ir/x/w/co/pw_chrono/public/pw_chrono/system_clock.h