CMSIS-RTOS2  Version 2.1.2
Real-Time Operating System: API and RTX Reference Implementation
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Timer Management

Create and control timer and timer callback functions. More...

Data Structures

struct  osTimerAttr_t
 Attributes structure for timer. More...
 

Typedefs

typedef void * osTimerId_t
 
typedef void(* osTimerFunc_t )(void *argument)
 Timer callback function. More...
 

Enumerations

enum  osTimerType_t {
  osTimerOnce = 0,
  osTimerPeriodic = 1
}
 Timer type. More...
 

Functions

osTimerId_t osTimerNew (osTimerFunc_t func, osTimerType_t type, void *argument, const osTimerAttr_t *attr)
 Create and Initialize a timer. More...
 
const char * osTimerGetName (osTimerId_t timer_id)
 Get name of a timer. More...
 
osStatus_t osTimerStart (osTimerId_t timer_id, uint32_t ticks)
 Start or restart a timer. More...
 
osStatus_t osTimerStop (osTimerId_t timer_id)
 Stop a timer. More...
 
uint32_t osTimerIsRunning (osTimerId_t timer_id)
 Check if a timer is running. More...
 
osStatus_t osTimerDelete (osTimerId_t timer_id)
 Delete a timer. More...
 

Description

In addition to the Generic Wait Functions CMSIS-RTOS also supports virtual timer objects. These timer objects can trigger the execution of a function (not threads). When a timer expires, a callback function is executed to run associated code with the timer. Each timer can be configured as a one-shot or a periodic timer. A periodic timer repeats its operation until it is deleted or stopped. All timers can be started, restarted, or stopped.

Note
RTX handles Timers in the thread osRtxTimerThread. Callback functions run under control of this thread and may use other CMSIS-RTOS API calls. The osRtxTimerThread is configured in Timer Configuration.
Timer management functions cannot be called from Interrupt Service Routines.

The figure below shows the behavior of a periodic timer. For one-shot timers, the timer stops after execution of the callback function.

Timer.png
Behavior of a Periodic Timer

Working with Timers

The following steps are required to use a software timer:

  1. Define the timers:
    osTimerId_t one_shot_id, periodic_id;
  2. Define callback functions:
    static void one_shot_Callback (void *argument) {
    int32_t arg = (int32_t)argument; // cast back argument '0'
    // do something, i.e. set thread/event flags
    }
    static void periodic_Callback (void *argument) {
    int32_t arg = (int32_t)argument; // cast back argument '5'
    // do something, i.e. set thread/event flags
    }
  3. Instantiate and start the timers:
    // creates a one-shot timer:
    one_shot_id = osTimerNew(one_shot_Callback, osTimerOnce, (void *)0, NULL); // (void*)0 is passed as an argument
    // to the callback function
    // creates a periodic timer:
    periodic_id = osTimerNew(periodic_Callback, osTimerPeriodic, (void *)5, NULL); // (void*)5 is passed as an argument
    // to the callback function
    osTimerStart(one_shot_id, 500);
    osTimerStart(periodic_id, 1500);
    // start the one-shot timer again after it has triggered the first time:
    osTimerStart(one_shot_id, 500);
    // when timers are not needed any longer free the resources:
    osTimerDelete(one_shot_id);
    osTimerDelete(periodic_id);

Data Structure Documentation

struct osTimerAttr_t
Data Fields
const char * name name of the timer

Pointer to a string with a human readable name of the timer object.
Default: NULL.

uint32_t attr_bits attribute bits

Reserved for future use (set to '0').
Default: 0.

void * cb_mem memory for control block

Pointer to a memory location for the timer control block object. This can optionally be used for custom memory management systems.
Default: NULL (uses kernel memory management).

uint32_t cb_size size of provided memory for control block

The size of the memory block passed with cb_mem. Must be the size of a timer control block object or larger.

Typedef Documentation

Timer ID identifies the timer.

Instances of this type hold a reference to a timer object.
Returned by:

void(* osTimerFunc_t)(void *argument)

The timer callback function is called everytime the timer elapses.

The callback might be executed either in a dedicated timer thread or in interrupt context. Thus it is recommended to only use ISR callable functions from the timer callback.

Parameters
[in]argumentThe argument provided to osTimerNew.

Enumeration Type Documentation

The osTimerType_t specifies the a repeating (periodic) or one-shot timer for the function osTimerNew.

Enumerator
osTimerOnce 

One-shot timer.

The timer is not automatically restarted once it has elapsed. It can be restarted manually using osTimerStart as needed.

osTimerPeriodic 

Repeating timer.

The timer repeats automatically and triggers the callback continuously while running, see osTimerStart and osTimerStop.

Function Documentation

osTimerId_t osTimerNew ( osTimerFunc_t  func,
osTimerType_t  type,
void *  argument,
const osTimerAttr_t attr 
)
Parameters
[in]funcfunction pointer to callback function.
[in]typeosTimerOnce for one-shot or osTimerPeriodic for periodic behavior.
[in]argumentargument to the timer callback function.
[in]attrtimer attributes; NULL: default values.
Returns
timer ID for reference by other functions or NULL in case of error.

The function osTimerNew creates an one-shot or periodic timer and associates it with a callback function with argument. The timer is in stopped state until it is started with osTimerStart. The function can be safely called before the RTOS is started (call to osKernelStart), but not before it is initialized (call to osKernelInitialize).

The function osTimerNew returns the pointer to the timer object identifier or NULL in case of an error.

Note
This function cannot be called from Interrupt Service Routines.

Code Example

#include "cmsis_os2.h"
void Timer1_Callback (void *arg); // prototypes for timer callback function
void Timer2_Callback (void *arg);
uint32_t exec1; // argument for the timer call back function
uint32_t exec2; // argument for the timer call back function
void TimerCreate_example (void) {
osTimerId_t id1; // timer id
osTimerId_t id2; // timer id
// Create one-shoot timer
exec1 = 1;
id1 = osTimerNew (Timer1_Callback, osTimerOnce, &exec1, NULL);
if (id1 != NULL) {
// One-shoot timer created
}
// Create periodic timer
exec2 = 2;
id2 = osTimerNew (Timer2_Callback, osTimerPeriodic, &exec2, NULL);
if (id2 != NULL) {
// Periodic timer created
}
:
}
*const char * osTimerGetName ( osTimerId_t  timer_id)
Parameters
[in]timer_idtimer ID obtained by osTimerNew.
Returns
name as NULL terminated string.

The function osTimerGetName returns the pointer to the name string of the timer identified by parameter timer_id or NULL in case of an error.

Note
This function cannot be called from Interrupt Service Routines.
osStatus_t osTimerStart ( osTimerId_t  timer_id,
uint32_t  ticks 
)
Parameters
[in]timer_idtimer ID obtained by osTimerNew.
[in]tickstime ticks value of the timer.
Returns
status code that indicates the execution status of the function.

The function osTimerStart starts or restarts a timer specified by the parameter timer_id. The parameter ticks specifies the value of the timer in time ticks.

Possible osStatus_t return values:

  • osOK: the specified timer has been started or restarted.
  • osErrorISR: osTimerStart cannot be called from interrupt service routines.
  • osErrorParameter: parameter timer_id is either NULL or invalid or ticks is incorrect.
  • osErrorResource: the timer specified by parameter timer_id is in an invalid timer state.
Note
This function cannot be called from Interrupt Service Routines.

Code Example

#include "cmsis_os2.h"
void Timer_Callback (void *arg) { // timer callback function
// arg contains &exec
// called every second after osTimerStart
}
uint32_t exec; // argument for the timer call back function
void TimerStart_example (void) {
osTimerId_t id; // timer id
uint32_t timerDelay; // timer value
osStatus_t status; // function return status
// Create periodic timer
exec = 1;
id = osTimerNew (Timer_Callback, osTimerPeriodic, &exec, NULL);
if (id) {
timerDelay = 1000;
status = osTimerStart (id, timerDelay); // start timer
if (status != osOK) {
// Timer could not be started
}
}
;
}
osStatus_t osTimerStop ( osTimerId_t  timer_id)
Parameters
[in]timer_idtimer ID obtained by osTimerNew.
Returns
status code that indicates the execution status of the function.

The function osTimerStop stops a timer specified by the parameter timer_id.

Possible osStatus_t return values:

  • osOK: the specified timer has been stopped.
  • osErrorISR: osTimerStop cannot be called from interrupt service routines.
  • osErrorParameter: parameter timer_id is either NULL or invalid.
  • osErrorResource: the timer specified by parameter timer_id is not running (you can only stop a running timer).
Note
This function cannot be called from Interrupt Service Routines.

Code Example

#include "cmsis_os2.h"
void Timer_Callback (void *arg); // prototype for timer callback function
uint32_t exec; // argument for the timer call back function
void TimerStop_example (void) {
osTimerId_t id; // timer id
osStatus_t status; // function return status
// Create periodic timer
exec = 1;
id = osTimerNew (Timer_Callback, osTimerPeriodic, &exec, NULL);
osTimerStart (id, 1000); // start timer
:
status = osTimerStop (id); // stop timer
if (status != osOK) {
// Timer could not be stopped
}
;
osTimerStart (id, 1000); // start timer again
;
}
uint32_t osTimerIsRunning ( osTimerId_t  timer_id)
Parameters
[in]timer_idtimer ID obtained by osTimerNew.
Returns
0 not running, 1 running.

The function osTimerIsRunning checks whether a timer specified by parameter timer_id is running. It returns 1 if the timer is running and 0 if the timer is stopped or an error occurred.

Note
This function cannot be called from Interrupt Service Routines.
osStatus_t osTimerDelete ( osTimerId_t  timer_id)
Parameters
[in]timer_idtimer ID obtained by osTimerNew.
Returns
status code that indicates the execution status of the function.

The function osTimerDelete deletes the timer specified by parameter timer_id.

Possible osStatus_t return values:

  • osOK: the specified timer has been deleted.
  • osErrorISR: osTimerDelete cannot be called from interrupt service routines.
  • osErrorParameter: parameter timer_id is either NULL or invalid.
  • osErrorResource: the timer specified by parameter timer_id is in an invalid timer state.
Note
This function cannot be called from Interrupt Service Routines.

Code Example

#include "cmsis_os2.h"
void Timer_Callback (void *arg); // prototype for timer callback function
uint32_t exec; // argument for the timer call back function
void TimerDelete_example (void) {
osTimerId_t id; // timer id
osStatus_t status; // function return status
// Create periodic timer
exec = 1;
id = osTimerNew (Timer_Callback, osTimerPeriodic, &exec, NULL);
osTimerStart (id, 1000UL); // start timer
;
status = osTimerDelete (id); // stop and delete timer
if (status != osOK) {
// Timer could not be deleted
}
;
}