# Development Guidelines
## Available APIs
The following table describes APIs available for the OpenHarmony LiteOS-M software timer module. For more details about the APIs, see the API reference.
**Table 1** Software timer APIs
Category
API
Description
Creating or deleting timers
LOS_SwtmrCreate
Creates a software timer.
LOS_SwtmrDelete
Deletes a software timer.
Starting or stopping timers
LOS_SwtmrStart
Starts a software timer.
LOS_SwtmrStop
Stop a software timer.
Obtaining remaining ticks of a software timer
LOS_SwtmrTimeGet
Obtains the number of remaining ticks of a software timer.
## How to Develop
The typical development process of software timers is as follows:
1. Configure the software timer.
- Check that **LOSCFG\_BASE\_CORE\_SWTMR** and **LOSCFG\_BASE\_IPC\_QUEUE** are set to **1**.
- Configure **LOSCFG\_BASE\_CORE\_SWTMR\_LIMIT** \(maximum number of software timers supported by the system\).
- Configure **OS\_SWTMR\_HANDLE\_QUEUE\_SIZE** \(maximum length of the software timer queue\).
2. Call **LOS\_SwtmrCreate** to create a software timer.
- Create a software timer with the specified timing duration, timeout handling function, and triggering mode.
- Return the function execution result \(success or failure\).
3. Call **LOS\_SwtmrStart** to start the software timer.
4. Call **LOS\_SwtmrTimeGet** to obtain the remaining number of ticks of the software timer.
5. Call **LOS\_SwtmrStop** to stop the software timer.
6. Call **LOS\_SwtmrDelete** to delete the software timer.
> **NOTE:**
>- Avoid too many operations in the callback function of the software timer. Do not use APIs or perform operations that may cause task suspension or blocking.
>- The software timers use a queue and a task resource of the system. The priority of the software timer tasks is set to **0** and cannot be changed.
>- The number of software timer resources that can be configured in the system is the total number of software timer resources available to the entire system, not the number of software timer resources available to users. For example, if the system software timer occupies one more resource, the number of software timer resources available to users decreases by one.
>- If a one-shot software timer is created, the system automatically deletes the timer and reclaims resources after the timer times out and the callback function is executed.
>- For a one-shot software timer that will not be automatically deleted after expiration, you need to call **LOS\_SwtmrDelete** to delete it and reclaim the timer resource to prevent resource leakage.
## Development Example
### Example Description
The following programming example demonstrates how to:
1. Create, start, delete, pause, and restart a software timer.
2. Use a one-shot software timer and a periodic software timer
### Sample Code
Prerequisites
- In **los\_config.h**, **LOSCFG\_BASE\_CORE\_SWTMR** is enabled.
- In **los\_config.h**, **LOSCFG\_BASE\_CORE\_SWTMR\_ALIGN** is disabled. The sample code does not involve timer alignment.
- The maximum number of software timers supported by the system \(**LOSCFG\_BASE\_CORE\_SWTMR\_LIMIT**\) is configured.
- The maximum length of the software timer queue \(OS\_SWTMR\_HANDLE\_QUEUE\_SIZE\) is configured.
The sample code is as follows:
```
#include "los_swtmr.h"
/* Timer count */
UINT32 g_timerCount1 = 0;
UINT32 g_timerCount2 = 0;
/* Task ID*/
UINT32 g_testTaskId01;
void Timer1_Callback(UINT32 arg) // Callback function 1
{
UINT32 tick_last1;
g_timerCount1++;
tick_last1 = (UINT32)LOS_TickCountGet(); // Obtain the current number of ticks.
printf("g_timerCount1=%d, tick_last1=%d\n", g_timerCount1, tick_last1);
}
void Timer2_Callback(UINT32 arg) // Callback function 2
{
UINT32 tick_last2;
tick_last2 = (UINT32)LOS_TickCountGet();
g_timerCount2++;
printf("g_timerCount2=%d tick_last2=%d\n", g_timerCount2, tick_last2);
}
void Timer_example(void)
{
UINT32 ret;
UINT32 id1; // timer id1
UINT32 id2; // timer id2
UINT32 tickCount;
/* Create a one-shot software timer, with the number of ticks set to 1000. When the number of ticks reaches 1000, callback function 1 is executed. */
LOS_SwtmrCreate(1000, LOS_SWTMR_MODE_ONCE, Timer1_Callback, &id1, 1);
/* Create a periodic software timer and execute callback function 2 every 100 ticks. */
LOS_SwtmrCreate(100, LOS_SWTMR_MODE_PERIOD, Timer2_Callback, &id2, 1);
printf("Timer 1 created.\n");
LOS_SwtmrStart(id1); // Start the one-shot software timer.
printf("Timer 1 started.\n");
LOS_TaskDelay(200); // Delay 200 ticks.
LOS_SwtmrTimeGet(id1, &tickCount); // Obtain the number of remaining ticks of the one-short software timer.
printf("tickCount=%d\n", tickCount);
LOS_SwtmrStop(id1); // Stop the software timer.
printf("Timer 1 stopped.\n");
LOS_SwtmrStart(id1);
LOS_TaskDelay(1000);
LOS_SwtmrStart(id2); // Start the periodic software timer.
printf("Timer 2 started.\n");
LOS_TaskDelay(1000);
LOS_SwtmrStop(id2);
ret = LOS_SwtmrDelete(id2); // Delete the software timer.
if (ret == LOS_OK) {
printf("Timer 2 deleted.\n");
}
}
UINT32 Example_TaskEntry(VOID)
{
UINT32 ret;
TSK_INIT_PARAM_S task1;
/* Lock task scheduling. */
LOS_TaskLock();
/* Create task 1. */
(VOID)memset(&task1, 0, sizeof(TSK_INIT_PARAM_S));
task1.pfnTaskEntry = (TSK_ENTRY_FUNC)Timer_example;
task1.pcName = "TimerTsk";
task1.uwStackSize = LOSCFG_BASE_CORE_TSK_DEFAULT_STACK_SIZE;
task1.usTaskPrio = 5;
ret = LOS_TaskCreate(&g_testTaskId01, &task1);
if (ret != LOS_OK) {
printf("Failed to create the timer task.\n");
return LOS_NOK;
}
/* Unlock task scheduling. */
LOS_TaskUnlock();
return LOS_OK;
}
```
### Verification
The output is as follows:
```
Timer 1 created.
Timer 1 started.
tickCount=798
Timer 1 stopped.
g_timerCount1=1, tick_last1=1208
Timer 2 started.
g_timerCount2=1 tick_last2=1313
g_timerCount2=2 tick_last2=1413
g_timerCount2=3 tick_last2=1513
g_timerCount2=4 tick_last2=1613
g_timerCount2=5 tick_last2=1713
g_timerCount2=6 tick_last2=1813
g_timerCount2=7 tick_last2=1913
g_timerCount2=8 tick_last2=2013
g_timerCount2=9 tick_last2=2113
g_timerCount2=10 tick_last2=2213
Timer 2 deleted.
```