Preface

  Open a special topic , Record your own learning STm32 The process of . A lot of information comes from previous notes and excerpts , I don't remember the specific source of some documents and knowledge points . If there is your hard work and the source is not indicated , Please contact me .
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  （ Only the most basic concepts and operations of some peripherals are listed here , Registers are just a part of the list , For detailed study, please refer to the official manual and check the source code ）
  For peripherals, use , Generally, you need to understand the basic concept and principle of peripherals , Learn about related registers . When using , First initialize the clock , Then initialize （ To configure ） peripherals , If used to GPIO To initialize the corresponding port and reuse it as the corresponding function , Finally, if you need to use interrupts , The interrupt should be turned on , Write interrupt handling functions . After initialization, we can use the corresponding library functions in the main logic code and use the corresponding peripherals to complete our functional requirements .

1. What is the clock source ？

  Clock is the basis of MCU operation , The clock signal pushes each part of the MCU to execute the corresponding instructions .
  The system clock , Is the processor runtime benchmark （ One clock cycle per machine instruction ）
 STM32 The main purpose of clock system is to provide clock for relatively independent peripheral modules , It is also to reduce the energy consumption of the whole chip .
  Different function modules have different clock upper limits , Therefore, different clocks are provided , More functional modules can also be placed in a single chip microcomputer .
  Add on and off functions for clocks of different modules , It can reduce the power consumption of MCU
 STM32 For low power consumption , He set all peripheral clocks to disable( Do not enable ), What peripherals are used , Just turn on the clock of the corresponding peripheral , Other unused items can still be disable( Do not enable ), This will reduce energy consumption .（ This is why no matter what function you configure, you need to turn on the corresponding clock first ）
Clock source ：
HSI、HSE、LSI、LSE、
PLL（ Lord PLL and I2S Part of it is dedicated to PLLI2S and SAI Part of it is dedicated to PLLSAI）
Look at the clock tree SYSCLK The clock source can have three options HSI HSE PLL
Here we generally choose HSE（ High speed external clock source ）
It can be seen that the maximum clock frequency of the system can be set to 168MHz
It can also be found in the chip manual
STM32F407 Schematic diagram ：
View external HSE Crystal vibration is 8Hz LSE by 32.768Hz( If there is This value is fixed )

CubeMX On the configuration
Configure our high-speed clock source as HSE
// Configure our low-speed clock source as LSE

choose HSE As SYSCLK Clock source To configure SYSCLK by 168MHz
The generated code

void SystemClock_Config(void)
{
  RCC_OscInitTypeDef RCC_OscInitStruct = {0};
  RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};

  /** Configure the main internal regulator output voltage
  */
  __HAL_RCC_PWR_CLK_ENABLE();
  __HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE1);
  /** Initializes the RCC Oscillators according to the specified parameters
  * in the RCC_OscInitTypeDef structure.
  */
  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;
  RCC_OscInitStruct.HSEState = RCC_HSE_ON;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
  RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
  RCC_OscInitStruct.PLL.PLLM = 8;
  RCC_OscInitStruct.PLL.PLLN = 336;
  RCC_OscInitStruct.PLL.PLLP = RCC_PLLP_DIV2;
  RCC_OscInitStruct.PLL.PLLQ = 4;
  if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
  {
    Error_Handler();
  }
  /** Initializes the CPU, AHB and APB buses clocks
  */
  RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
                              |RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
  RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
  RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
  RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV4;
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV2;

  if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_5) != HAL_OK)
  {
    Error_Handler();
  }
}