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Timer Management
[Nut/OS API]

Collaboration diagram for Timer Management:

Detailed Description

Asynchronous timer support.

The timer management provides functions to start and stop asynchronous timers, determine the CPU speed and let a thread give up the CPU for a specified time period.


Functions

u_long NutTimerMillisToTicks (u_long ms)
 Create an asynchronous timer.
HANDLE NutTimerStart (u_long ms, void(*callback)(HANDLE, void *), void *arg, u_char flags)
HANDLE NutTimerStartTicks (u_long ticks, void(*callback)(HANDLE, void *), void *arg, u_char flags)
void NutSleep (u_long ms)
 Temporarily suspends the current thread.
void NutTimerStopAsync (HANDLE handle)
 Asynchronously stop a specified timer.
void NutTimerStop (HANDLE handle)
 Stop a specified timer.
u_long NutGetCpuClock (void)
 Return the CPU clock in Hertz.
u_long NutGetTickCount (void)
 Return the number of timer ticks.
u_long NutGetSeconds (void)
 Return the seconds counter value.
u_long NutGetMillis (void)
 Return the milliseconds counter value.

Variables

NUTTIMERINFO *volatile nutTimerList
 Linked list of all system timers.
NUTTIMERINFO *volatile nutTimerPool
volatile u_char ms62_5
 System tick counter.

Function Documentation

u_long NutGetCpuClock (  void   ) 
 

Return the CPU clock in Hertz.

Returns:
CPU clock frequency in Hertz.

u_long NutGetMillis (  void   ) 
 

Return the milliseconds counter value.

This function returns the value of a counter, which is incremented every system timer tick. During system start, the counter is cleared to zero and will overflow roughly after 49.7 days. The resolution is depends on system ticks.

Note:
There is intentionally no provision to modify the seconds counter. Callers can rely on a continuous update and use this value for system tick independend timeout calculations.
Returns:
Value of the seconds counter.

u_long NutGetSeconds (  void   ) 
 

Return the seconds counter value.

This function returns the value of a counter, which is incremented every second. During system start, the counter is cleared to zero.

Note:
There is intentionally no provision to modify the seconds counter. Callers can rely on a continuous update and use this value for system tick independend timeout calculations. Applications, which want to use this counter for date and time functions, should use an offset value.
Returns:
Value of the seconds counter.

u_long NutGetTickCount (  void   ) 
 

Return the number of timer ticks.

This function returns the TickCount since the system was started. It is limited to the resolution of the system timer.

Returns:
Number of ticks.

void NutSleep (  u_long  ms  ) 
 

Temporarily suspends the current thread.

Causes the current thread to wait for a specified interval or, if the specified interval is zero, to give up the CPU for another thread with higher or same priority.

This function may switch to another application thread, that got the same or a higher priority and is ready to run.

Note:
Threads may sleep longer than the specified number of milliseconds, depending on the number of threads with higher or equal priority, which are ready to run. If you need exact timing, use NutDelay().

Parameters:
ms Milliseconds to sleep. Granularity is 62.5 ms. If 0, the current thread will not sleep, but may give up the CPU.

u_long NutTimerMillisToTicks (  u_long  ms  ) 
 

Create an asynchronous timer.

The function returns immediately, while the timer runs asynchronously in the background.

The timer counts for a specified number of milliseconds, then calls the callback routine with a given argument.

The callback function is executed in interrupt context at a very high priority. It can call only a limited set of functions and must return as soon as possible.

Parameters:
ms Specifies the timer interval in milliseconds.
callback Identifies the function to be called on each timer interval.
arg The argument passed to the callback function.
flags If set to TM_ONESHOT, the timer will be stopped after the first interval. Set to 0 for periodic timers.
Returns:
Timer handle if successfull, 0 otherwise. The handle may be used to stop the timer by calling TimerStop.

void NutTimerStop (  HANDLE  handle  ) 
 

Stop a specified timer.

Only periodic timers need to be stopped. One-shot timers are automatically stopped by the timer management after ther first timer interval. Anyway, long running one-shot timers may be stopped to release the occupied memory.

Parameters:
handle Identifies the timer to be stopped. This handle must have been created by calling NutTimerStart().

void NutTimerStopAsync (  HANDLE  handle  ) 
 

Asynchronously stop a specified timer.

Stops one-shot and periodic timers.

Note:
It is save to call this function from within an interrupt handler. The memory occupied by the timer is not released, but added to a pool and will be re-used by the next timer being created. In any case interrupts should be disabled when calling this function.
Parameters:
handle Identifies the timer to be stopped. This handle must have been created by calling NutTimerStart().

Variable Documentation

volatile u_char ms62_5
 

System tick counter.

For the time being we put this here to ensure that it will be placed in lower RAM. This is essential for the AVR platform, where we use this counter to determine the system clock and calculate the correct baudrate factors. If this counter would be placed in external RAM, additional wait states may apply.

NUTTIMERINFO* volatile nutTimerPool
 

This pool is used to collect released memory from elapsed timers. It's required because we can't free memory in interrupt context.