SysTick功能总结

一、初始化SysTick

按1ms来设置systick，也可以除以1000000。按1us来设置

1. SysTick_Config(SystemCoreClock / 1000); //SysTick开启系统tick定时器并初始化其中断，1ms

二、systick的函数

1. // cycles per microsecond
2. static volatile uint32_t usTicks = 0;
3. // current uptime for 1kHz systick timer. will rollover after 49 days. hopefully we won't care.
4. volatile uint32_t sysTickUptime = 0;
5. // SysTick
6. void SysTick_Handler(void)
7. {
8. sysTickUptime++;
9. }
10. //delay ms
11. void DelayMs(uint16_t nms)
12. {
13. uint32_t t0=micros();
14. while(micros() - t0 < nms * 1000);
15. }
16. // Return system uptime in microseconds (rollover in 70minutes)
17. //返回 us
18. uint32_t micros(void)
19. {
20. register uint32_t ms, cycle_cnt;
21. do {
22. ms = sysTickUptime;
23. cycle_cnt = SysTick->VAL;
24. } while (ms != sysTickUptime);
25. return (ms * 1000) + (usTicks * 1000 - cycle_cnt) / usTicks;
26. }
27. // Return system uptime in milliseconds (rollover in 49 days)
28. uint32_t millis(void)
29. {
30. return sysTickUptime;
31. }

systick启动后会进入SysTick_Handler()的中断，

三、少了重要的一部，哭~T.T

开启RCC时钟！！！！！

1. void cycleCounterInit(void)
2. {
3. RCC_ClocksTypeDef clocks;
4. RCC_GetClocksFreq(&clocks);
5. usTicks = clocks.SYSCLK_Frequency / 1000000;
6. }

遇到的错误：我在初始化MPU6050时，写入数据特别慢。明明计时都准的，不知道为什么特别慢。其他还都能顺利运行。

最后发现时RCC的时钟有问题。