Stm32--- systick timer

brief introduction

Systick Timer , It's a simple timer , about CM3,CM4 Kernel chip , There are Systick Timer .

Systick Timers are often used to delay , Or the heartbeat clock of the real-time system . This can save MCU resources , Don't waste a timer . such as UCOS in , Time division multiplexing , Need a minimum timestamp , Generally in STM32+UCOS In the system , All use Systick do UCOS Heartbeat clock .

Systick The timer is the system tick timer , One 24 Bit countdown timer , Count 0 when , Will be taken from RELOAD The initial value of the automatic reload timing in the register . As long as you don't put it in SysTick Enable bits in the control and status registers are cleared , Never stop , Works even in sleep mode .

SysTick The timer is tied to NVIC in , Used to produce SYSTICK abnormal （ Exception number ：15）.
Systick The priority of interrupts can also be set .

working principle

The system timer triggers 1KHz The interrupt , Interrupt cycle time
T= 1/f =1000ms/1000=1ms
The system timer is connected to PLL Output 72MHz The clock
As long as the system timer 72000000 Times count , Namely 1 The arrival of seconds
As long as the system timer 72000 Times count , Namely 1ms The arrival of time
As long as the system timer 72 Times count , Namely 1us The arrival of time

SysTick_Config(SystemCoreClock/1000);

Systick register

CTRL -> SysTick Control and status registers
LOAD -> SysTick Auto reload division register
VAL -> SysTick Current value register
CALIB -> SysTick Calibration value register

SysTick Control and status registers - CTRL

about STM32, The external clock source is HCLK(AHB Bus clock ） Of 1/8 The kernel clock is HCLK The clock
Configuration function ：SysTick_CLKSourceConfig();

SysTick Reload the load value register - LOAD

SysTick Current value register - VAL

In the firmware library Systick Correlation function

SysTick_CLKSourceConfig()    //Systick Clock source selection  misc.c In file 

SysTick_Config(uint32_t ticks) // initialization systick, The clock is HCLK, And turn on the interrupt 
                                                //core_cm3.h/core_cm4.h In file 

Systick Interrupt service function ：

   void SysTick_Handler(void);