STM32 笔记：时钟配置

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void SystemClock_Config(void)
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{
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  /* RCC振荡器配置结构体 */
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  RCC_OscInitTypeDef RCC_OscInitStruct = {0};
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  /* RCC总线时钟配置结构体 */
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  RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};
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  /** Configure the main internal regulator output voltage
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  */
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    //使能 PWR电源控制模块时钟。
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  __HAL_RCC_PWR_CLK_ENABLE();
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    //168M
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  __HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE1);
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  /** Initializes the RCC Oscillators according to the specified parameters
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  * in the RCC_OscInitTypeDef structure.
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  */
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  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;//外部高速晶振
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  RCC_OscInitStruct.HSEState = RCC_HSE_ON;
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  RCC_OscInitStruct.HSIState = RCC_HSI_OFF;//关闭内部高速RC振荡
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  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
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  RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;//PLL源
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  RCC_OscInitStruct.PLL.PLLM = 8;
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  RCC_OscInitStruct.PLL.PLLN = 336;
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  RCC_OscInitStruct.PLL.PLLP = RCC_PLLP_DIV2;
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  RCC_OscInitStruct.PLL.PLLQ = 7;
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  if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
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  {
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    Error_Handler();
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  }
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  /** Initializes the CPU, AHB and APB buses clocks
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  */
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  RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
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                              |RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
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  RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;//系统时钟来自 PLL
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  RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;//168M
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  RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV4;//42M
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  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV2;//84M
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  if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_5) != HAL_OK)
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  {
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    Error_Handler();
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  }
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}

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//计时1us
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void cycleCounterInit(void)
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{
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    usTicks=SystemCoreClock / 1000000U; //168M/1000000
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    CoreDebug->DEMCR |= CoreDebug_DEMCR_TRCENA_Msk;//打开 DWT
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    DWT->CYCCNT = 0;
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    DWT->CTRL |= DWT_CTRL_CYCCNTENA_Msk;//启动周期计数器
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}
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/*使用DWT->CYCCNT*/
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uint32_t start = DWT->CYCCNT;
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/* 要测试的代码 */
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foo();
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uint32_t end = DWT->CYCCNT;