Timer

Hardware Interface

Defined in namespace hal

#include <libhal/timer.hpp>

class timer

Timer hardware abstraction interface.

Use this interface for devices and peripherals that have timer like capabilities, such that, when a timer’s time has expired, an event, interrupt, or signal is generated.

Timer drivers tick period must be an integer multiple of 1 nanosecond, meaning that the only tick period allowed are 1ns, 2ns, up to the maximum holdable in a std::chrono::nanosecond type. sub-nanosecond tick periods are not allowed.

Subclassed by hal::soft::inert_timer

Public Functions

inline result<is_running_t> is_running()

Determine if the timer is currently running.

Returns:

result<is_running_t> - information about the timer

inline result<cancel_t> cancel()

Stops a scheduled event from happening.

Does nothing if the timer is not currently running.

Note that there must be sufficient time between the this call finishing and the scheduled event’s termination. If this call is too close to when the schedule event expires, this function may not complete before the hardware calls the callback.

Returns:

result<cancel_t> - success or failure

inline result<schedule_t> schedule(hal::callback<void(void)> p_callback, hal::time_duration p_delay)

Schedule an callback be be executed after the delay time.

If this is called and the timer has already scheduled an event (in other words, is_running() returns true), then the previous scheduled event will be canceled and the new scheduled event will be started.

If the delay time result in a tick period of 0, then the timer will execute after 1 tick period. For example, if the tick period is 1ms and the requested time delay is 500us, then the event will be scheduled for 1ms.

If the tick period is 1ms and the requested time is 2.5ms then the event will be scheduled after 2 tick periods or in 2ms.

Parameters:

• p_callback – - callback function to be called when the timer expires

• p_delay – - the amount of time until the timer expires

Throws:

out_of_bounds_error – - if p_interval is greater than what can be cannot be achieved

Returns:

result<schedule_t> - success or failure

struct cancel_t

Feedback from cancelling a timer.

This structure is currently empty as no feedback has been determined for now. This structure may be expanded in the future.

struct is_running_t

Feedback after checking if the timer is running.

Public Members

bool is_running

Determines if the timer is currently running.

If this value is false, then the timer is not running. If this value is true, then the timer is currently running and a callback is scheduled to be executed at some point in the future.

struct out_of_bounds_error

Error type indicating that the desired time delay is not achievable with this timer.

This occurs if the time delay is too large based on the tick period of the timer.

Public Members

std::chrono::nanoseconds tick_period

The tick period.

std::chrono::nanoseconds maximum

The maximum possible delay allowed.

struct schedule_t

Feedback from scheduling a timer.

This structure is currently empty as no feedback has been determined for now. This structure may be expanded in the future.