Stm32f4xx that thing. (ii)--configuration of the system clock

Every time I contact a new microcontroller, I will be very curious how many MHz the microcontroller's system clock, how to reach the maximum system clock described in datasheet, the microcontroller's peripheral clock will be how many MHz it? If I want to use delay, how can I write a program to achieve a precise delay? I think these are the questions I need to know before I start contacting a new microcontroller.

For each ARM CORTEX-M series SCM, manufacturers in order to better promote their own microcontroller, at the same time to facilitate the use of designers, reduce product development cycle, will be the microcontroller peripheral related registers and peripherals related functions are implemented and packaged, on the official website free for everyone to use. The standard peripheral Library of the STM32F405RG also contains various operational functions with DSP cores. If required, you can ttp://www2.st.com/content/st_com/en/products/embedded-software/mcus-embedded-software/from H stm32-embedded-software/stm32-standard-peripheral-libraries/stsw-stm32065.html# download.

If you use the standard peripherals Library, we can follow the code analysis in the system_stm32f4xx.c file in the standard Peripherals Library:

#if  defined (stm32f40_41xxx)  | |  defined (stm32f427_437xx)  | |  defined (stm32f429_439xx)  | |  defined (stm32f401xx)  | |  defined (stm32f469_479xx)   #define  pll_m      25#elif defined   (stm32f446xx)   #define  PLL_M      8#elif defined  ( STM32F410XX)  | |  defined  (stm32f411xe)   #if  defined (use_hse_bypass)    #define  PLL_M       8      #else  /* ! use_hse_bypass */   #define  PLL_M      16  #endif  /*  use_hse_bypass */#else #endif#if defined  (stm32f40_41xxx) #define  PLL_N       336/* sysclk = pll_vco / pll_p */#define  PLL_P       2#endif#if defined (stm32f40_41xxx)   uint32_t systemcoreclock = 168000000; #endif 

According to the programming Manual on the contents of the clock Register,

Pll_vco = (Hse_value or hsi_value/pll_m) * Pll_n

sysclk=pll_vco/pll_p

, Hse_value represents the frequency of the single-chip external crystal oscillator, Hsi_value represents the frequency of the internal oscillator, the experiment board using the external 25MHz crystal oscillator, according to the configuration of the program, we can calculate the Systemcoreclock = 168000000.

This article is from the "intentions to create" blog, please be sure to keep this source http://chasingdreams.blog.51cto.com/2790339/1768816

Stm32f4xx that thing. (ii)--configuration of the system clock