Stm32's five clock source parameter setting experience

1. In STM32 , there are five clock sources, HSI , HSE , LSI , LSE , and PLL .

1 HSI is a high speed internal clock, RC oscillator with a frequency of 8MHz .

2 HSE is a high-speed external clock that can be connected to a quartz / ceramic resonator or an external clock source with a frequency range of 4MHz to 16MHz .

3 LSI is a low-speed internal clock, RC oscillator with a frequency of 40kHz .

4 LSE is a low-speed external clock connected to a quartz crystal with a frequency of 32.768kHz .

5 PLL is the phase-locked loop multiplier output, and its clock input source can be selected as HSI/2 , HSE or HSE/2 . The multiplier can be selected from 2 to 16 times, but its output frequency must not exceed 72MHz .

2. If the external crystal oscillator is not used on the STM32, the connection of OSC_IN and OSC_OUT: If the internal RC oscillator is used instead of the external crystal oscillator, please proceed as follows:

1 For 100- pin or 144- pin products, OSC_IN should be grounded and OSC_OUT should be left floating. 2 For products with less than 100 feet, there are 2 ways to connect: 1st: OSC_IN and OSC_OUT are grounded through 10K resistors respectively . This method can improve EMC performance; the second kind: remap OSC_IN and OSC_OUT to PD0 and PD1 respectively , then configure PD0 and PD1 as push-pull outputs and output '0' . This method can reduce power consumption and (relative to the above) save 2 external resistors.

Third, use HSE clock, program to set the clock parameter flow : 01 , reset the RCC register to the default value     RCC_DeInit; 02 , open the external high-speed clock crystal oscillator HSE RCC_HSEConfig (RCC_HSE_ON); 03 , wait for the external high-speed clock crystal to work      HSEStartUpStatus = RCC_WaitForHSEStartUp(); 04 , set AHB clock           RCC_HCLKConfig; 05 , set the high speed AHB clock       RCC_PCLK2Config; 06 , set the low speed AHB clock     RCC_PCLK1Config ; 07 , set PLL RCC_PLLConfig; 08 , turn on PLL RCC_PLLCmd (ENABLE); 09 , wait for PLL to work     While(RCC_GetFlagStatus(RCC_FLAG_PLLRDY) == RESET) 10 , set the system clock          RCC_SYSCLKConfig; 11 , to determine whether the PLL is the system clock       While(RCC_GetSYSCLKSource() != 0x08) 12 , open the peripheral clock to be used      RCC_APB2PeriphClockCmd()/RCC_APB1PeriphClockCmd()

Fourth, the following is the configuration function of RCC in the program of STM32 software firmware library ( using external 8MHz crystal oscillator )

/************************************************* ******************************

* Function Name : RCC_Configuration

* Description : RCC configuration ( using an external 8MHz crystal )

* Input : None

* Output : None

* Return : None

************************************************** *****************************/

Void RCC_Configuration(void)

{

/* Reset the peripheral RCC register to the default value */

RCC_DeInit();

/* Set external high speed crystal oscillator ( HSE ) */

RCC_HSEConfig(RCC_HSE_ON); //RCC_HSE_ON —— HSE crystal on (ON)

   /* Wait for HSE to start */

HSEStartUpStatus = RCC_WaitForHSEStartUp();

If(HSEStartUpStatus == SUCCESS) //SUCCESS : HSE crystal is stable and ready

{

    /* Set AHB clock ( HCLK ) */

RCC_HCLKConfig(RCC_SYSCLK_Div1); //RCC_SYSCLK_Div1——AHB clock = system clock

     / * Set the high speed AHB clock ( PCLK2 ) * /

RCC_PCLK2Config(RCC_HCLK_Div1); //RCC_HCLK_Div1——APB2 clock = HCLK

     /* Set low speed AHB clock ( PCLK1 ) */

RCC_PCLK1Config(RCC_HCLK_Div2); //RCC_HCLK_Div2——APB1 clock = HCLK / 2

    / * Set the number of FLASH memory delay clock cycles * /

FLASH_SetLatency(FLASH_Latency_2); //FLASH_Latency_2 2 delay period

   

/ * Select FLASH prefetch refers to the mode of the cache * /

FLASH_PrefetchBufferCmd(FLASH_PrefetchBuffer_Enable); // Prefetch refers to cache enable

     /* Set PLL clock source and multiplication factor */

RCC_PLLConfig(RCC_PLLSource_HSE_Div1, RCC_PLLMul_9);

// PLL input clock = HSE clock frequency; RCC_PLLMul_9 - PLL input clock x 9

   

/* Enable PLL */

RCC_PLLCmd(ENABLE);

     /* Check if the specified RCC flag (PLL ready flag ) is set or not */

While(RCC_GetFlagStatus(RCC_FLAG_PLLRDY) == RESET)

{

}

     /* Set the system clock ( SYSCLK ) */

RCC_SYSCLKConfig(RCC_SYSCLKSource_PLLCLK);

//RCC_SYSCLKSource_PLLCLK - select PLL as system clock

    /* PLL returns the clock source used as the system clock */

While(RCC_GetSYSCLKSource() != 0x08) //0x08 : PLL as system clock

{

}

}

/* Enable or disable APB2 peripheral clock */

RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA | RCC_APB2Periph_GPIOB |

RCC_APB2Periph_GPIOC , ENABLE);

//RCC_APB2Periph_GPIOA GPIOA clock

//RCC_APB2Periph_GPIOB GPIOB clock

//RCC_APB2Periph_GPIOC GPIOC clock

//RCC_APB2Periph_GPIOD GPIOD clock

}

Fifth, the clock frequency

The internal 8M internal oscillation of the STM32F103 can reach 72M after multiplying. At present, TI's M3 series chips can reach a maximum frequency of 80M.

The selection of the clock frequency in the stm32 firmware library 3.0 has been greatly simplified, and a lot of the original operations are performed in the background. The function given by the system is SystemInit(). However, some macro definition settings need to be made before the call, and the specific settings are in the system_stm32f10x.c file.

There is one such definition at the beginning of the file: //#define SYSCLK_FREQ_HSE HSE_Value //#define SYSCLK_FREQ_20MHz 20000000 //#define SYSCLK_FREQ_36MHz 36000000 //#define SYSCLK_FREQ_48MHz 48000000 //#define SYSCLK_FREQ_56MHz 56000000 #define SYSCLK_FREQ_72MHz 72000000

ST's officially recommended external crystal oscillator is 8M, so the library function settings assume that your hardware has been connected to the 8M crystal oscillator. The above is the default crystal oscillator 8M, the recommended CPU frequency selection. Here choose: # Define SYSCLK_FREQ_72MHz 72000000 That is, the maximum value of the 103 series can reach 72M.

Then the C file continue to look down #elif defined SYSCLK_FREQ_72MHz const uint32_t SystemFrequency = SYSCLK_FREQ_72MHz; const uint32_t SystemFrequency_SysClk = SYSCLK_FREQ_72MHz; const uint32_t SystemFrequency_AHBClk = SYSCLK_FREQ_72MHz; const uint32_t SystemFrequency_APB1Clk = (SYSCLK_FREQ_72MHz / 2); const uint32_t SystemFrequency_APB2Clk = SYSCLK_FREQ_72MHz;

This is the speed of each system when defining the CPU running 72M. They are: hardware frequency, system clock, AHB bus frequency, APB1 bus frequency, APB2 bus frequency . Look down, see this: # Elif defined SYSCLK_FREQ_72MHz static void SetSysClockTo72(void);

This is the function that sets the clock when defining 72M. This function is called by the SetSysClock() function, and the SetSysClock() function is called by the SystemInit() function. Finally, the SystemInit() function is called by you.

So the process of setting the system clock is: First, the user program calls the SystemInit() function, which is a library function. Then, after the necessary initialization of some registers is performed in the SystemInit() function, the SetSysClock() function is called. SetSysClock() function According to the macro definition of #define SYSCLK_FREQ_72MHz 72000000, I know that I want to call the SetSysClockTo72() function, so I have a bunch of troublesome and complicated settings~!@#$%^ Then, the CPU runs, and the speed is 72M. It’s a bit cumbersome, but everyone just needs to know that the user has to set the frequency, and the program will do two things:

First: system_stm32f10x.c #define SYSCLK_FREQ_72MHz 72000000 Second: Call SystemInit()