STM32官方例程，滴答时钟，可利用系统内的滴答进行延时，更加准确-This example shows how to configure the SysTick to generate a time base equal to

1 ms. The system clock is set to 24 MHz on Value line devices and to 72 MHz on

other devices, the SysTick is clocked by the AHB clock (HCLK).



A "Delay" function is implemented based on the SysTick end-of-count event.

Four LEDs are toggled with a timing defined by the Delay function.