RCC introduction of Hal Library

One 、RCC Clock tree overview

There are four clock input sources .
Selectors 、( pre ) Frequency divider and frequency multiplier .
Final set frequency .
SYSCLK The system clock

SYSCLK There are three ways to get ：
1、HSI The internal high-speed clock uses RC oscillator , The frequency is 8M, Accuracy is not high , Without frequency divider and frequency multiplier , In this way SYSCLK The clock is 8M
2、HSE The external high-speed clock is generally externally connected 4-16MHZ Crystal oscillator , Due to the use of external crystal oscillator , So the accuracy is greatly improved , But it increases the cost , In this way SYSCLK The clock and HSE The clock frequency is the same , Is the external crystal oscillator frequency , It's usually 8M
3、 adopt PLLCLK obtain , This way is through the frequency divider 、 The clock obtained after the frequency multiplier and selector are allocated . Its input clock is HSI or HSE, Due to the addition of frequency divider and frequency multiplier , So what you get SYSCLK The clock can be overclocked or down clocked ,STM32F103 maximal SYSCLK by 72MHZ.
HCLK The clock

HCLK Clock pass SYSCLK After frequency division, we get , Generally will HCLK and SYSCLK Set to consistent

FCLK The clock

FCLK The frequency and HCLK Always consistent

PCLK The clock

PCLK Provide clock for MCU peripherals , It is divided into PCLK1 and PCLK2
APB1 The maximum clock frequency of the peripheral is 36MHZ

RTC The clock

Independent watchdog clock