callback_timer_interrupt

A software timer class that can manage up to 254 timers. Each one may be repeating or single shot.
When a timer triggers it will call the selected function. The function may be a class member or free function.
The timers are driven from a call to tick(uint32_t count). This call would normally be made from a high priority interrupt routine. The destination function will receive the callback in the same context as the tick call.
The call to tick has a low overhead when a timer is not ‘due’. Internally the timers are stored in ‘first timeout’ order so only the head of the list needs to be checked.

Each timer may have a period of up to 2³²-2 ticks (4,294,967,294).
At 1ms per tick this would equate to just over 49 days.

The framework relies on a supplied interrupt enable/disable guard type. With this mechanism, calls to tick are disabled if certain member functions are called. If the program flow is within a disable/enable section when the timer interrupt is activated then the tick update will be deferred until the next tick period. The timer interrupt may interrogate the return value of tick() to check whether the update was deferred. The guard allows timer functions to be to be called from the callback called by tick().

Defines the following classes

etl::icallback_timer_atomic<uint_least8_t MAX_TIMERS, typename TInterruptGuard>
etl::callback_timer_atomic<typename TInterruptGuard>

Uses definitions from timer.h.

Important
For correct operation of the timer framework, the routine that calls tick must not be preemptible by another routine that calls a timer function. Also, calls to the timer framework may only be made from the caller of tick and one other, lower priority, thread of execution.

icallback_timer_interrupt

The base class for all timer controllers.

Template parameters
MAX_TIMERS The number of timers to be supported. The maximum number is 254.
A value of 255 will result in a compile error.

TInterruptGuard The type that enables/disables interrupts.

Type definitions

callback_type etl::delegate<void(void)>

The function type used for callbacks.

Member functions

etl::timer::id::type register_timer(callback_type callback,
                                    uint32_t      period,                                        
                                    bool          repeating)

Description
Registers a timer calling a free or static function.

Parameters
callback A delegate to the callback function that will be called when the timer expires.
period The timer period in ticks.
repeating false if single shot, true if repeating.

Return
The allocated timer id or etl::timer::mode::NO_TIMER if one was not available.

bool unregister_timer(etl::timer::id::type id)

Unregisters a timer.
If the timer is active then it will be stopped.
Returns true if a timer with the id was successfully unregistered.

void enable(bool state)

Description
Enables or disables the timer manager according to the state.

bool is_running() const

Description
Returns true if the timer manager is enabled.

void clear()

Description
Clears the callback timer back to the initial state. All timers will be stopped and unregistered.

bool tick(uint32_t count)

Description
This function updates the internal tick counter (if enabled) and must pass the number of ticks that have occurred since the last call. If the count encompasses more than one period of a repeating timer then the timer will be triggered multiple times in one call to tick.
Returns true if the tick counter was updated, otherwise false. This may be used by the calling routine to accumulate unprocessed tick counts.

bool start(etl::timer::id::type id, bool immediate = false)

Description
Starts the timer with the specified id.
If the timer is already running then the timer Is restarted from the current tick count.
If immediate is true then the timer is triggered on the next call to tick(). Note: Single shot timers will only trigger once.
If the id does not correspond to a registered timer then returns false.

bool stop(etl::timer::id::type id)

Description
Stops the timer with the specified id.
Does nothing if the timer is already stopped.
if the id does not correspond to a registered timer then returns false.

bool set_period(etl::timer::id::type id, uint32_t period)

Description
Stops the timer with the specified id.
Sets a new timer period.
Returns true if successful.

bool set_mode(etl::timer::id::type id, bool repeating)

Description
Stops the timer with the specified id.
Sets a new timer mode.
Returns true if successful.

etl::timer::id::type time_to_next()

Description
Returns the time to the next timeout.
From: 20.38.0

Constants

MAX_TIMERS The maximum number of timer that can be handled.

callback_timer_atomic

Template parameters
MAX_TIMERS The number of timers to be supported. The maximum number is 254.
A value of 255 will result in a compile error.

TInterruptGuard The type that enables/disables interrupts.

message_timer_interrupt()

Description
Default constructor.

Example

//***************************************************************************
// Class callback via etl::function
//***************************************************************************
class Test
{
public:

  Test()
    : ticks(0)
  {
  }

  void callback()
  {
    ++ticks;
  }

  int ticks;
};
  
Test test;

//***************************************************************************
// The interrupt guard type.
// Saves and disables on contruction.
// Restores on destruction.
//***************************************************************************
struct InterruptGuard
{
  InterruptGuard()
  {
    state = __save_interrupts();
    __disable_interrupts();
  }

  ~InterruptGuard()
  {
    __restore_interrupts(state);
  }

  int state;
};

using callback_type = etl::icallback_timer_atomic<InterruptGuard>::callback_type;

callback_type member_callback = callback_type::create<Test, test, &Test::callback> member_callback;

//***************************************************************************
// Free function callback via etl::function
//***************************************************************************
int free_ticks1 = 0;

void free_callback1()
{
  ++free_ticks;
}

callback_type free_callback1 = callback_type::create<free_function_callback>();

//***************************************************************************
// Free function callback via function pointer
//***************************************************************************
int free_ticks2 = 0;

void free_callback2()
{
  ++free_ticks2;
}

//***************************************************************************
// Timer controller.
//***************************************************************************
etl::callback_timer_atomic<2, InterruptGuard> timer_controller;

//***************************************************************************
// The main loop.
//***************************************************************************
int main()
{
  etl::timer::id::type id1 = timer_controller.register_timer(member_callback,
                                                             1000,
                                                             etl::timer::mode::SINGLE_SHOT);

  etl::timer::id::type id2 = timer_controller.register_timer(free_function_callback,
                                                             100,
                                                             etl::timer::mode::REPEATING);

  timer_controller.start(id1);
  timer_controller.start(id2);

  timer_controller.enable(true);

  // Start timer interrupts here.

  while (true)
  {
    // Loop forever.
  }

  return 0;
}

//***************************************************************************
// The interrupt timer callback.
//***************************************************************************
void timer_interrupt()
{
  const uint32_t TICK = 1;
  static uint32_t nticks = TICK;

  if (timer_controller.tick(nticks))
  {
    nticks = TICK;
  }
  else
  {
    nticks += TICK;
  }
}