Introduction to RT thread kernel (4) -- clock management

Timer management

Hardware timer ： The external crystal oscillator provides the chip input clock
Software timer ： Provided by the operating system , The unit is the time length of the clock beat , The timing value must be an integral multiple of the clock beat . The clock beat of the system is 10ms, The time setting of the soft timer must be 20ms,30ms etc. .

Two timer mechanisms ：
Single trigger timer ： Execute timer event only once , Then the timer stops automatically
Cycle triggered timer ： Periodically trigger timer events , The straightway user stops manually

HAED_TIMER Pattern （ The default mode ）
The timer timeout function in this mode executes in the interrupt context , Can be initialized in / Use parameters when creating timers RT_TIMER_FLAG_HARD_TIMER To specify the .

SOFT_TIMER Pattern
Define by macro RT_USING_TIMER_SOFT To decide whether to enable the mode . When this mode is enabled , The system will create a timer Threads , then SOFT_TIMER The timer timeout function of mode will be in timer Execute in the context of thread . Can be initialized in / Use parameters when creating timers RT_TIMER_FLAG_SOFT_TIMER To specify the settings SOFT_TIMER Pattern .

Timer control block :

struct rt_timer
typedef struct rt_timer *rt_timer_t

Timer management mode ：
Initialize the timer ：

void rt_system_timer_init(void);

SOFT_TIMER initialization ：

void rt_system_timer_thread_init(void);

Timer creation ：

rt_timer_t rt_timer_create()

Timer deletion ( Free memory )

rt_err_t rt_timer_delete(rt_timer_t timer);

Timer initialization ：

rt_timer_init() 

Timer disengagement :（ Don't free memory ）

rt_err_t rt_timer_detach(rt_timer_t timer);

Start timer ：

rt_err_t rt_timer_start(rt_timer_t timer);

Stop timer ：

rt_err_t rt_timer_stop(rt_timer_t timer);

Control timer function interface ：
You can view and modify the timer settings according to the parameters of the command type

rt_err_t rt_timer_control(rt_timer_t timer, rt_uint8_t cmd, void* arg);
 Parameters ：timer, Timer handle 
cmd	 Commands for controlling timers , Currently, four commands are supported , Set the timing time , Check the timing , Set single trigger , Set cycle trigger 
arg	 And  cmd  Corresponding control command parameters   such as ,cmd  When setting timeout for , You can pass the timeout parameter through  arg  To set 

cmd command ：
#define RT_TIMER_CTRL_SET_TIME 0x0 /* Set timer timeout /
#define RT_TIMER_CTRL_GET_TIME 0x1 / Get timer timeout /
#define RT_TIMER_CTRL_SET_ONESHOT 0x2 / Set the timer to a single timer /
#define RT_TIMER_CTRL_SET_PERIODIC 0x3 / Set the timer to periodic timer */

High precision delay
Use timer delay because each time the delay time is an integral multiple of the clock beat , If you need more accurate delay , You need to read the count of the hardware timer or directly use the hardware timer

stay Cortex-M In the series ,SysTick Has been RT-Thread Used as a OS Tick Use , It is configured to 1/RT_TICK_PER_SECOND The way to trigger an interrupt after seconds , The interrupt handler function uses Cortex-M3 default SysTick_Handler name . stay Cortex-M3 Of CMSIS（Cortex Microcontroller Software Interface Standard） It is stipulated in the specification that SystemCoreClock Represents the dominant frequency of the chip , So based on the SysTick as well as SystemCoreClock, We can use SysTick Obtain an accurate delay function , As shown in the following example ,Cortex-M3 Based on SysTick Precise delay （ The system is required to enable SysTick After use ）：