stm32-learning experience summary——UCOSIII-software timer

1. Software Timer Introduction 
UC/OS-III provides software timer service. The essence of timer is a decrementing counter. When the counter is reduced to 0, it can trigger the execution of some action. This action is implemented through callback function. The callback function is defined by the user. It can be a simple LED light or a motor. When the timer is finished, the defined callback function will be called immediately. The application can have any number of timers. 
Note! Do not use blocking calls or functions that can block or delete timer tasks in the callback function, such as: OSTimeDly() OSTimeDlyHMSM() and other functions. 
The relevant code of UCOSIII's software timer service is in the OS_TIMR.c file. When OS_CFG_TMR_EN in OS_CFG.H is set to 1, the software timer service is enabled. The 
time resolution of the timer in UCOSIII depends on the time base frequency, that is, the value of OS_CFG_TMR_TASK_RATE_HZ, in HZ. If the time base frequency is set to 10Hz, the resolution of all timers is one tenth of a second.

Common functions of software timer: 
1. OSTmrCreate() creates a timer and specifies the operation mode 
2. OSTmrDel() deletes the timer 
3. OSTmrRemainGet() gets the remaining time of the timer 
4. OSTmrStart() starts the timer counting 
5. OSTmrStateGet() gets the current timer status 
6. OSTmrStop() stops the countdown of the timer

Before using the timer, you must call the OSTmrCreate() function to create it and set related parameters. The function prototype is as follows:

OSTmrCreate (OS_TMR *p_tmr, (1)
             CPU_CHAR *p_name, (2)
             OS_TICK dly, (3)
             OS_TICK period, (4)
             OS_OPT opt, (5)
             OS_TMR_CALLBACK_PTR p_callback, (6)
             void *p_callback_arg, (7)
             OS_ERR *p_err) (8)

The meaning of each parameter: 
(1): Timer, you need to define it yourself, such as: OS_TMR tmr1; //Define a timer 1 
(2): The name of the timer; 
(3): Set the period of the timer's first operation; 
(4): Set the period of the timer's operation after the second operation; 
(5): Configuration mode: OS_OPT_TMR_ONE_SHOT: Single timer 
OS_OPT_TMR_PERIODIC: Periodic mode 
(6): Timer callback function; 
(7): Timer transfer parameters; 
(8): Returned error code;

Note: 
When opt is set to a single timer: the timer starts counting down from the initial value (that is, the parameter dly in the OSTmrCreate() function) until it reaches 0, the callback function is called and the timer stops. The timer of a single timer is executed only once. 
When opt is in periodic mode, when the countdown is completed, the timer calls the callback function, resets the counter and restarts the timing, and continues in a cycle. If the parameter dly is set to 0 when calling the function OSTmrCreate() to create a periodic timer, then each cycle of the timer is period. 
As shown in the following figure: 
Single timer mode, only executed once 
 
. In the same single timer mode, when the timer is working, calling the OSTmrStart() function will restart the timer, as shown in the following figure. 
 
In periodic mode, there are two types: initial delay and no initial delay. When there is an initial delay, when the countdown is completed, the timer calls the callback function, resets the counter and restarts the timing, and continues in a cycle. If the parameter dly is set to 0 when calling the function OSTmrCreate() to create a periodic timer, then each cycle of the timer is period. As shown in the figure below, 
 
when there is no initial delay, the function OSTmrCreate() parameter dly is used to determine the first cycle, and the counter value is reset to period at the beginning of each subsequent cycle. 

Finally, I attach the source code for creating a software timer

    OSTmrCreate((OS_TMR *)&tmr1,    

                (CPU_CHAR *)"tmr1",       

                (OS_TICK) 20,           

                (OS_TICK) 100,         

                (OS_OPT )OS_OPT_TMR_PERIODIC, 

                (OS_TMR_CALLBACK_PTR)tmr1_callback,

                (void *)0,            

                (OS_ERR *)&err);