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1# Software Timer
2
3
4## Basic Concepts<a name="section4118241563"></a>
5
6The software timer is a software-simulated timer based on system tick interrupts. When the preset tick counter value has elapsed, the user-defined callback will be invoked. The timing precision is related to the cycle of the system tick clock. Due to the limitation in hardware, the number of hardware timers cannot meet users' requirements. Therefore, the OpenHarmony LiteOS-A kernel provides the software timer function. The software timer allows more timing services to be created, increasing the number of timers.
7
8The software timer supports the following functions:
9
10-   Disabling the software timer using a macro
11-   Creating a software timer
12-   Starting a software timer
13-   Stopping a software timer
14-   Deleting a software timer
15-   Obtaining the number of remaining ticks of a software timer
16
17## Working Principles<a name="section31079397569"></a>
18
19The software timer is a system resource. When modules are initialized, a contiguous section of memory is allocated for software timers. The maximum number of timers supported by the system is configured by the  **LOSCFG\_BASE\_CORE\_SWTMR\_LIMIT**  macro in  **los\_config.h**. Software timers use a queue and a task resource of the system. The software timers are triggered based on the First In First Out \(FIFO\) rule. For the timers set at the same time, the timer with a shorter value is always closer to the queue head than the timer with a longer value, and is preferentially triggered. The software timer counts time in ticks. When a software timer is created and started, the OpenHarmony system determines the timer expiry time based on the current system time \(in ticks\) and the timing interval set by the user, and adds the timer control structure to the global timing list.
20
21When a tick interrupt occurs, the tick interrupt handler scans the global timing list for expired timers. If such timers are found, the timers are recorded.
22
23When the tick interrupt handling function is complete, the software timer task \(with the highest priority\) is woken up. In this task, the timeout callback function for the recorded timer is called.
24
25Timer States
26
27-   OS\_SWTMR\_STATUS\_UNUSED
28
29    The timer is not in use. When the timer module is initialized, all timer resources in the system are set to this state.
30
31-   OS\_SWTMR\_STATUS\_CREATED
32
33    The timer is created but not started or the timer is stopped. When  **LOS\_SwtmrCreate**  is called for a timer that is not in use or  **LOS\_SwtmrStop**  is called for a newly started timer, the timer changes to this state.
34
35-   OS\_SWTMR\_STATUS\_TICKING
36
37    The timer is running \(counting\). When  **LOS\_SwtmrStart**  is called for a newly created timer, the timer enters this state.
38
39
40Timer Modes
41
42The OpenHarmony provides three types of software timers:
43
44-   One-shot timer: Once started, the timer is automatically deleted after triggering only one timer event.
45-   Periodic timer: This type of timer periodically triggers timer events until it is manually stopped.
46-   One-shot timer deleted by calling an API
47
48## Development Guidelines<a name="section18576131520577"></a>
49
50### Available APIs<a name="section3138019145719"></a>
51
52The following table describes APIs available for the OpenHarmony LiteOS-A software timer module. For more details about the APIs, see the API reference.
53
54**Table  1**  Software timer APIs
55
56<a name="table107038227425"></a>
57<table><thead align="left"><tr id="row2704122217420"><th class="cellrowborder" valign="top" width="20.6020602060206%" id="mcps1.2.4.1.1"><p id="p57041622144212"><a name="p57041622144212"></a><a name="p57041622144212"></a>Function</p>
58</th>
59<th class="cellrowborder" valign="top" width="29.542954295429542%" id="mcps1.2.4.1.2"><p id="p19704142216424"><a name="p19704142216424"></a><a name="p19704142216424"></a>API</p>
60</th>
61<th class="cellrowborder" valign="top" width="49.85498549854985%" id="mcps1.2.4.1.3"><p id="p670412224217"><a name="p670412224217"></a><a name="p670412224217"></a>Description</p>
62</th>
63</tr>
64</thead>
65<tbody><tr id="row1470413222429"><td class="cellrowborder" rowspan="2" valign="top" width="20.6020602060206%" headers="mcps1.2.4.1.1 "><p id="p8284115918428"><a name="p8284115918428"></a><a name="p8284115918428"></a>Creating or deleting timers</p>
66</td>
67<td class="cellrowborder" valign="top" width="29.542954295429542%" headers="mcps1.2.4.1.2 "><p id="p117045225428"><a name="p117045225428"></a><a name="p117045225428"></a>LOS_SwtmrCreate</p>
68</td>
69<td class="cellrowborder" valign="top" width="49.85498549854985%" headers="mcps1.2.4.1.3 "><p id="p170422234213"><a name="p170422234213"></a><a name="p170422234213"></a>Creates a software timer.</p>
70</td>
71</tr>
72<tr id="row11704102217425"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p1970492213426"><a name="p1970492213426"></a><a name="p1970492213426"></a>LOS_SwtmrDelete</p>
73</td>
74<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p870442211421"><a name="p870442211421"></a><a name="p870442211421"></a>Deletes a software timer.</p>
75</td>
76</tr>
77<tr id="row57041422184215"><td class="cellrowborder" rowspan="2" valign="top" width="20.6020602060206%" headers="mcps1.2.4.1.1 "><p id="p1476172124318"><a name="p1476172124318"></a><a name="p1476172124318"></a>Starting or stopping timers</p>
78</td>
79<td class="cellrowborder" valign="top" width="29.542954295429542%" headers="mcps1.2.4.1.2 "><p id="p167040225423"><a name="p167040225423"></a><a name="p167040225423"></a>LOS_SwtmrStart</p>
80</td>
81<td class="cellrowborder" valign="top" width="49.85498549854985%" headers="mcps1.2.4.1.3 "><p id="p1570412229421"><a name="p1570412229421"></a><a name="p1570412229421"></a>Starts a software timer.</p>
82</td>
83</tr>
84<tr id="row15704172224219"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p1170422214216"><a name="p1170422214216"></a><a name="p1170422214216"></a>LOS_SwtmrStop</p>
85</td>
86<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p17705122211426"><a name="p17705122211426"></a><a name="p17705122211426"></a>Stops a software timer.</p>
87</td>
88</tr>
89<tr id="row12705222154214"><td class="cellrowborder" valign="top" width="20.6020602060206%" headers="mcps1.2.4.1.1 "><p id="p0705622134214"><a name="p0705622134214"></a><a name="p0705622134214"></a>Obtaining remaining ticks of a software timer</p>
90</td>
91<td class="cellrowborder" valign="top" width="29.542954295429542%" headers="mcps1.2.4.1.2 "><p id="p177052220424"><a name="p177052220424"></a><a name="p177052220424"></a>LOS_SwtmrTimeGet</p>
92</td>
93<td class="cellrowborder" valign="top" width="49.85498549854985%" headers="mcps1.2.4.1.3 "><p id="p3705122264210"><a name="p3705122264210"></a><a name="p3705122264210"></a>Obtains the number of remaining ticks of a software timer.</p>
94</td>
95</tr>
96</tbody>
97</table>
98
99### How to Develop<a name="section1344817403575"></a>
100
101The typical development process of software timers is as follows:
102
1031.  Configure the software timer.
104    -   Check that  **LOSCFG\_BASE\_CORE\_SWTMR**  and  **LOSCFG\_BASE\_IPC\_QUEUE**  are enabled.
105    -   Configure  **LOSCFG\_BASE\_CORE\_SWTMR\_LIMIT**  \(maximum number of software timers supported by the system\).
106    -   Configure  **OS\_SWTMR\_HANDLE\_QUEUE\_SIZE**  \(maximum length of the software timer queue\).
107
1082.  Call  **LOS\_SwtmrCreate**  to create a software timer.
109    -   Create a software timer with the specified timing duration, timeout handling function, and triggering mode.
110    -   Return the function execution result \(success or failure\).
111
1123.  Call  **LOS\_SwtmrStart**  to start the software timer.
1134.  Call  **LOS\_SwtmrTimeGet**  to obtain the remaining number of ticks of the software timer.
1145.  Call  **LOS\_SwtmrStop**  to stop the software timer.
1156.  Call  **LOS\_SwtmrDelete**  to delete the software timer.
116
117>![](../public_sys-resources/icon-note.gif) **NOTE:**
118>-   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.
119>-   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.
120>-   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.
121>-   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.
122>-   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.
123
124### Development Example<a name="section114416313585"></a>
125
126Prerequisites:
127
128-   In  **los\_config.h**,  **LOSCFG\_BASE\_CORE\_SWTMR**  is enabled.
129-   The maximum number of software timers supported by the system \(**LOSCFG\_BASE\_CORE\_SWTMR\_LIMIT**\) is configured.
130-   The maximum length of the software timer queue \(**OS\_SWTMR\_HANDLE\_QUEUE\_SIZE**\) is configured.
131
132**Sample Code**
133
134```
135#include "los_swtmr.h"
136
137void Timer1_Callback(uint32_t arg);
138void Timer2_Callback(uint32_t arg);
139
140UINT32 g_timercount1 = 0;
141UINT32 g_timercount2 = 0;
142
143void Timer1_Callback(uint32_t arg) // Callback function 1
144{
145    unsigned long tick_last1;
146    g_timercount1++;
147    tick_last1=(UINT32)LOS_TickCountGet(); // Obtain the current number of ticks.
148    PRINTK("g_timercount1=%d\n",g_timercount1);
149    PRINTK("tick_last1=%d\n",tick_last1);
150}
151
152void Timer2_Callback(uint32_t arg) // Callback function 2
153{
154    unsigned long tick_last2;
155    tick_last2=(UINT32)LOS_TickCountGet();
156    g_timercount2 ++;
157    PRINTK("g_timercount2=%d\n",g_timercount2);
158    PRINTK("tick_last2=%d\n",tick_last2);
159}
160
161void Timer_example(void)
162{
163    UINT16 id1;
164    UINT16 id2; // timer id
165    UINT32 uwTick;
166
167    /* 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. */
168    LOS_SwtmrCreate (1000, LOS_SWTMR_MODE_ONCE, Timer1_Callback, &id1, 1);
169
170    /* Create a periodic software timer and execute callback function 2 every 100 ticks. */
171    LOS_SwtmrCreate(100, LOS_SWTMR_MODE_PERIOD, Timer2_Callback, &id2, 1);
172    PRINTK("create Timer1 success\n");
173
174    LOS_SwtmrStart (id1); // Start the one-shot software timer.
175    dprintf("start Timer1 success\n");
176    LOS_TaskDelay(200); // Delay 200 ticks.
177    LOS_SwtmrTimeGet(id1, &uwTick); // Obtain the number of remaining ticks of the one-short software timer.
178    PRINTK("uwTick =%d\n", uwTick);
179
180    LOS_SwtmrStop(id1); // Stop the software timer.
181    PRINTK("stop Timer1 success\n");
182
183    LOS_SwtmrStart(id1);
184    LOS_TaskDelay(1000);
185    LOS_SwtmrDelete(id1); // Delete the software timer.
186    PRINTK("delete Timer1 success\n");
187
188    LOS_SwtmrStart(id2); // Start the periodic software timer.
189    PRINTK("start Timer2\n");
190
191    LOS_TaskDelay(1000);
192    LOS_SwtmrStop(id2);
193    LOS_SwtmrDelete(id2);
194}
195```
196
197**Output**
198
199```
200create Timer1 success
201start Timer1 success
202uwTick =800
203stop Timer1 success
204g_timercount1=1
205tick_last1=1201
206delete Timer1 success
207start Timer2
208g_timercount2 =1
209tick_last1=1301
210g_timercount2 =2
211tick_last1=1401
212g_timercount2 =3
213tick_last1=1501
214g_timercount2 =4
215tick_last1=1601
216g_timercount2 =5
217tick_last1=1701
218g_timercount2 =6
219tick_last1=1801
220g_timercount2 =7
221tick_last1=1901
222g_timercount2 =8
223tick_last1=2001
224g_timercount2 =9
225tick_last1=2101
226g_timercount2 =10
227tick_last1=2201
228```
229
230