前言
在看STM32H743I-EVAL2板子的知识点例程。数了一下，好像有100多个demo.
现在看RCC_ClockConfig例程。里面用到了上一个外部中断demo的知识点。
RCC_ClockConfig例程，通过外部中断(按钮)的响应，来动态切换时钟源到HSE, HSI, CSI.
知识点看明白了，但是不知道这个demo的应用场景。就没有用CubeMx重建工程，只看一下，知道有这回事。
有啥需求会动态切换时钟源呢? 一般时钟源用CubeMX配好，生成初始化代码，就不改了。
例程中，由CubeMx生成SystemClock_Config(), 在main函数中调用一下.
动态切换时钟源的函数为: SystemClockCSI_Config(), SystemClockHSI_Config(), SystemClockHSE_Config().
对这4个函数做个笔记。
试验
外部中断按下后，修改时钟源的顺序为 HSE(初始化时钟源为HSE), 按下按钮后，由外部中断响应函数动态修改时钟源的顺序为 HSE => HSI => CSI => HSE
/**
* @brief switch in system clock out of ISR context.
* @retval None
*/
static void SwitchSystemClock(void)
{
if (__HAL_RCC_GET_PLL_OSCSOURCE() == RCC_PLLSOURCE_HSI)
{
// 2. HSI => CSI
/* PLL source is HSI oscillator */
/* Set SYSCLK frequency to 400000000 Hz, coming from the PLL which is clocked by CSI */
SystemClockCSI_Config();
}
else if (__HAL_RCC_GET_PLL_OSCSOURCE() == RCC_PLLSOURCE_HSE)
{
// CubeMx配置的时钟源是HSE, 所以按下按键后，先执行的是这里 1. HSE => HSI
/* PLL source is HSE oscillator */
/* Set SYSCLK frequency to 400000000 Hz, coming from the PLL which is clocked by HSI */
SystemClockHSI_Config();
}
else if (__HAL_RCC_GET_PLL_OSCSOURCE() == RCC_PLLSOURCE_CSI)
{
/* PLL source is CSI oscillator */
/* Set SYSCLK frequency to 400000000 Hz, coming from the PLL which is clocked by HSE */
// 3. CSI => HSE 回到系统默认时钟源
SystemClockHSE_Config();
}
/* reset global variable */
SwitchClock = RESET;
}
初始化时钟源
/**
* @brief System Clock Configuration
* The system Clock is configured as follow :
* System Clock source = PLL (HSE)
* SYSCLK(Hz) = 400000000 (CPU Clock)
* HCLK(Hz) = 200000000 (AXI and AHBs Clock)
* AHB Prescaler = 2
* D1 APB3 Prescaler = 2 (APB3 Clock 100MHz)
* D2 APB1 Prescaler = 2 (APB1 Clock 100MHz)
* D2 APB2 Prescaler = 2 (APB2 Clock 100MHz)
* D3 APB4 Prescaler = 2 (APB4 Clock 100MHz)
* HSE Frequency(Hz) = 25000000
* PLL_M = 5
* PLL_N = 160
* PLL_P = 2
* PLL_Q = 4
* PLL_R = 2
* VDD(V) = 3.3
* Flash Latency(WS) = 4
* @param None
* @retval None
*/
static void SystemClock_Config(void)
{
RCC_ClkInitTypeDef RCC_ClkInitStruct;
RCC_OscInitTypeDef RCC_OscInitStruct;
/*!< Supply configuration update enable */
HAL_PWREx_ConfigSupply(PWR_LDO_SUPPLY);
/* The voltage scaling allows optimizing the power consumption when the device is
clocked below the maximum system frequency, to update the voltage scaling value
regarding system frequency refer to product datasheet. */
__HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE1);
while ((PWR->D3CR & (PWR_D3CR_VOSRDY)) != PWR_D3CR_VOSRDY) {}
/* Enable HSE Oscillator and activate PLL with HSE as source */
RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE; // 默认是使用HSE晶振
// 只打开HSE, 关掉(HSI, CSI)
RCC_OscInitStruct.HSEState = RCC_HSE_ON;
RCC_OscInitStruct.HSIState = RCC_HSI_OFF;
RCC_OscInitStruct.CSIState = RCC_CSI_OFF;
RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON; // 使用锁相环
RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE; // 锁相环的源是HSE
// 锁相环参数可以打开CubeMx看一下
RCC_OscInitStruct.PLL.PLLM = 5;
RCC_OscInitStruct.PLL.PLLN = 160;
RCC_OscInitStruct.PLL.PLLFRACN = 0;
RCC_OscInitStruct.PLL.PLLP = 2;
RCC_OscInitStruct.PLL.PLLR = 2;
RCC_OscInitStruct.PLL.PLLQ = 4;
RCC_OscInitStruct.PLL.PLLVCOSEL = RCC_PLL1VCOWIDE;
RCC_OscInitStruct.PLL.PLLRGE = RCC_PLL1VCIRANGE_2;
if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
{
while(1) {}
}
// 设置外设通道时钟(指定经过PLL后的分频系数)
/* Select PLL as system clock source and configure bus clocks dividers */
RCC_ClkInitStruct.ClockType = (
RCC_CLOCKTYPE_SYSCLK
| RCC_CLOCKTYPE_HCLK
| RCC_CLOCKTYPE_D1PCLK1
| RCC_CLOCKTYPE_PCLK1
| RCC_CLOCKTYPE_PCLK2
| RCC_CLOCKTYPE_D3PCLK1);
RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
RCC_ClkInitStruct.SYSCLKDivider = RCC_SYSCLK_DIV1;
RCC_ClkInitStruct.AHBCLKDivider = RCC_HCLK_DIV2;
RCC_ClkInitStruct.APB3CLKDivider = RCC_APB3_DIV2;
RCC_ClkInitStruct.APB1CLKDivider = RCC_APB1_DIV2;
RCC_ClkInitStruct.APB2CLKDivider = RCC_APB2_DIV2;
RCC_ClkInitStruct.APB4CLKDivider = RCC_APB4_DIV2;
// 设置是外设时钟通道
// FLASH_LATENCY_4 为闪存延迟要4个时钟周期
if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_4) != HAL_OK)
{
while(1) {}
}
}
切换时钟源 from CSI => HSE
/**
* @brief Switch the PLL source from CSI to HSE , and select the PLL as SYSCLK
* The system Clock is configured as follow :
* System Clock source = PLL (HSE)
* SYSCLK(Hz) = 400000000 (CPU Clock)
* HCLK(Hz) = 200000000 (AXI and AHBs Clock)
* AHB Prescaler = 2
* D1 APB3 Prescaler = 2 (APB3 Clock 100MHz)
* D2 APB1 Prescaler = 2 (APB1 Clock 100MHz)
* D2 APB2 Prescaler = 2 (APB2 Clock 100MHz)
* D3 APB4 Prescaler = 2 (APB4 Clock 100MHz)
* HSE Frequency(Hz) = 25000000
* PLL_M = 5
* PLL_N = 160
* PLL_P = 2
* PLL_Q = 4
* PLL_R = 2
* VDD(V) = 3.3
* Flash Latency(WS) = 4
* @param None
* @retval None
*/
static void SystemClockHSE_Config(void)
{
RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};
RCC_OscInitTypeDef RCC_OscInitStruct = {0};
// 现将时钟源切到CSI上, 才能修改时钟源(这是和第一次初始化时钟不一样的地方)
/* -1- Select CSI as system clock source to allow modification of the PLL configuration */
RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_SYSCLK;
RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_CSI;
if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_1) != HAL_OK)
{
/* Initialization Error */
Error_Handler();
}
/* -2- Enable HSE Oscillator, select it as PLL source and finally activate the PLL */
RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE; // 操作的时钟源为HSE
RCC_OscInitStruct.HSEState = RCC_HSE_ON; // HSE开
RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON; // PLL开
RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE; // PLL源为HSE
// 参照CubeMX图形化配置
RCC_OscInitStruct.PLL.PLLM = 5;
RCC_OscInitStruct.PLL.PLLN = 160;
RCC_OscInitStruct.PLL.PLLFRACN = 0;
RCC_OscInitStruct.PLL.PLLP = 2;
RCC_OscInitStruct.PLL.PLLR = 2;
RCC_OscInitStruct.PLL.PLLQ = 4;
RCC_OscInitStruct.PLL.PLLVCOSEL = RCC_PLL1VCOWIDE;
RCC_OscInitStruct.PLL.PLLRGE = RCC_PLL1VCIRANGE_2;
if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
{
/* Initialization Error */
Error_Handler();
}
// 设置设备通道时钟
/* Select PLL as system clock source and configure bus clocks clocks dividers */
RCC_ClkInitStruct.ClockType = (RCC_CLOCKTYPE_SYSCLK
| RCC_CLOCKTYPE_HCLK
| RCC_CLOCKTYPE_D1PCLK1
| RCC_CLOCKTYPE_PCLK1
| RCC_CLOCKTYPE_PCLK2
| RCC_CLOCKTYPE_D3PCLK1);
RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
RCC_ClkInitStruct.SYSCLKDivider = RCC_SYSCLK_DIV1;
RCC_ClkInitStruct.AHBCLKDivider = RCC_HCLK_DIV2;
RCC_ClkInitStruct.APB3CLKDivider = RCC_APB3_DIV2;
RCC_ClkInitStruct.APB1CLKDivider = RCC_APB1_DIV2;
RCC_ClkInitStruct.APB2CLKDivider = RCC_APB2_DIV2;
RCC_ClkInitStruct.APB4CLKDivider = RCC_APB4_DIV2;
if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_4) != HAL_OK)
{
/* Initialization Error */
Error_Handler();
}
// 只开HSE（关掉CSI, 因为上一个时钟源是CSI）
/* -4- Optional: Disable CSI Oscillator (if the HSI is no more needed by the application)*/
RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_CSI; // 操作的时钟源为CSI
RCC_OscInitStruct.CSIState = RCC_CSI_OFF; // 关掉CSI
RCC_OscInitStruct.PLL.PLLState = RCC_PLL_NONE; // 断开CSI和PLL的连接
if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
{
/* Initialization Error */
Error_Handler();
}
}
/**
* @brief Switch the PLL source from HSE to HSI, and select the PLL as SYSCLK
* source.
* System Clock source = PLL (HSI)
* SYSCLK(Hz) = 400000000 (CPU Clock)
* HCLK(Hz) = 200000000 (AXI and AHBs Clock)
* AHB Prescaler = 2
* D1 APB3 Prescaler = 2 (APB3 Clock 100MHz)
* D2 APB1 Prescaler = 2 (APB1 Clock 100MHz)
* D2 APB2 Prescaler = 2 (APB2 Clock 100MHz)
* D3 APB4 Prescaler = 2 (APB4 Clock 100MHz)
* HSI Frequency(Hz) = 64000000
* PLL_M = 16
* PLL_N = 200
* PLL_P = 2
* PLL_Q = 4
* PLL_R = 2
* VDD(V) = 3.3
* Flash Latency(WS) = 4
* @param None
* @retval None
*/
static void SystemClockHSI_Config(void)
{
RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};
RCC_OscInitTypeDef RCC_OscInitStruct = {0};
// 先指定一个和要修改的目标时钟源不同的时钟源，才能修改目标时钟源
// e.g. 要修改HSI为最终要用的时钟源，那先将时钟源设定为空闲的时钟源(e.g. 现在的时钟源为HSE, 要修改时钟源为HSI)
/* -1- Select HSE as system clock source to allow modification of the PLL configuration */
RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_SYSCLK;
RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_HSE;
if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_1) != HAL_OK)
{
/* Initialization Error */
Error_Handler();
}
/* -2- Enable HSI Oscillator, select it as PLL source and finally activate the PLL */
RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI;
RCC_OscInitStruct.HSIState = RCC_HSI_ON;
RCC_OscInitStruct.HSICalibrationValue = RCC_HSICALIBRATION_DEFAULT;
// 参照CubeMx图形化设置
RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSI;
RCC_OscInitStruct.PLL.PLLM = 16;
RCC_OscInitStruct.PLL.PLLN = 200;
RCC_OscInitStruct.PLL.PLLFRACN = 0;
RCC_OscInitStruct.PLL.PLLP = 2;
RCC_OscInitStruct.PLL.PLLR = 2;
RCC_OscInitStruct.PLL.PLLQ = 4;
RCC_OscInitStruct.PLL.PLLVCOSEL = RCC_PLL1VCOWIDE;
RCC_OscInitStruct.PLL.PLLRGE = RCC_PLL1VCIRANGE_2;
if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
{
/* Initialization Error */
Error_Handler();
}
/* Select PLL as system clock source and configure bus clocks clocks dividers */
// 设置设备时钟通道
RCC_ClkInitStruct.ClockType = (
RCC_CLOCKTYPE_SYSCLK
| RCC_CLOCKTYPE_HCLK
| RCC_CLOCKTYPE_D1PCLK1
| RCC_CLOCKTYPE_PCLK1
| RCC_CLOCKTYPE_PCLK2
| RCC_CLOCKTYPE_D3PCLK1);
RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
RCC_ClkInitStruct.SYSCLKDivider = RCC_SYSCLK_DIV1;
RCC_ClkInitStruct.AHBCLKDivider = RCC_HCLK_DIV2;
RCC_ClkInitStruct.APB3CLKDivider = RCC_APB3_DIV2;
RCC_ClkInitStruct.APB1CLKDivider = RCC_APB1_DIV2;
RCC_ClkInitStruct.APB2CLKDivider = RCC_APB2_DIV2;
RCC_ClkInitStruct.APB4CLKDivider = RCC_APB4_DIV2;
if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_4) != HAL_OK)
{
/* Initialization Error */
Error_Handler();
}
/* -4- Optional: Disable HSE Oscillator (if the HSE is no more needed by the application) */
// 关掉以前的时钟源(HSE).
RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;
RCC_OscInitStruct.HSEState = RCC_HSE_OFF;
RCC_OscInitStruct.PLL.PLLState = RCC_PLL_NONE;
if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
{
/* Initialization Error */
Error_Handler();
}
}
/**
* @brief Switch the PLL source from HSI to CSI, and select the PLL as SYSCLK
* source.
* System Clock source = PLL (CSI)
* SYSCLK(Hz) = 400000000 (CPU Clock)
* HCLK(Hz) = 200000000 (AXI and AHBs Clock)
* AHB Prescaler = 2
* D1 APB3 Prescaler = 2 (APB3 Clock 100MHz)
* D2 APB1 Prescaler = 2 (APB1 Clock 100MHz)
* D2 APB2 Prescaler = 2 (APB2 Clock 100MHz)
* D3 APB4 Prescaler = 2 (APB4 Clock 100MHz)
* CSI Frequency(Hz) = 4000000
* PLL_M = 1
* PLL_N = 200
* PLL_P = 2
* PLL_Q = 4
* PLL_R = 2
* VDD(V) = 3.3
* Flash Latency(WS) = 4
* @param None
* @retval None
*/
static void SystemClockCSI_Config(void)
{
RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};
RCC_OscInitTypeDef RCC_OscInitStruct = {0};
// 因为上一个时钟源是HSI(按钮按下的时钟源切换顺序为 HSE => HSI => CSI => HSE), 所以要先切到HSI
/* -1- Select HSI as system clock source to allow modification of the PLL configuration */
RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_SYSCLK;
RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_HSI;
if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_1) != HAL_OK)
{
/* Initialization Error */
Error_Handler();
}
/* -2- Enable CSI Oscillator, select it as PLL source and finally activate the PLL */
RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_CSI;
RCC_OscInitStruct.CSIState = RCC_CSI_ON;
RCC_OscInitStruct.CSICalibrationValue = RCC_CSICALIBRATION_DEFAULT;
RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_CSI;
RCC_OscInitStruct.PLL.PLLM = 1;
RCC_OscInitStruct.PLL.PLLN = 200;
RCC_OscInitStruct.PLL.PLLFRACN = 0;
RCC_OscInitStruct.PLL.PLLP = 2;
RCC_OscInitStruct.PLL.PLLR = 2;
RCC_OscInitStruct.PLL.PLLQ = 4;
RCC_OscInitStruct.PLL.PLLVCOSEL = RCC_PLL1VCOWIDE;
RCC_OscInitStruct.PLL.PLLRGE = RCC_PLL1VCIRANGE_2;
if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
{
/* Initialization Error */
Error_Handler();
}
/* Select PLL as system clock source and configure bus clocks clocks dividers */
RCC_ClkInitStruct.ClockType = (
RCC_CLOCKTYPE_SYSCLK
| RCC_CLOCKTYPE_HCLK
| RCC_CLOCKTYPE_D1PCLK1
| RCC_CLOCKTYPE_PCLK1
| RCC_CLOCKTYPE_PCLK2
| RCC_CLOCKTYPE_D3PCLK1);
RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
RCC_ClkInitStruct.SYSCLKDivider = RCC_SYSCLK_DIV1;
RCC_ClkInitStruct.AHBCLKDivider = RCC_HCLK_DIV2;
RCC_ClkInitStruct.APB3CLKDivider = RCC_APB3_DIV2;
RCC_ClkInitStruct.APB1CLKDivider = RCC_APB1_DIV2;
RCC_ClkInitStruct.APB2CLKDivider = RCC_APB2_DIV2;
RCC_ClkInitStruct.APB4CLKDivider = RCC_APB4_DIV2;
if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_4) != HAL_OK)
{
/* Initialization Error */
Error_Handler();
}
/* -4- Optional: Disable HSI Oscillator (if the HSI is no more needed by the application) */
// 关掉上一个时钟源HSI
RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI;
RCC_OscInitStruct.HSEState = RCC_HSI_OFF;
RCC_OscInitStruct.PLL.PLLState = RCC_PLL_NONE;
if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
{
/* Initialization Error */
Error_Handler();
}
}
总结
这个demo意义不大。
如果不借助CubeMx, 怎么来写时钟初始化? 那些分频，倍频系数(那么复杂的系数…)如何填写？
实际工程板子上，用的时钟源都是HSE上外接的晶振(为了时钟精确)，那为啥要切到片内晶振上呢?
如果外部晶振坏了，好像文档上说，STMCU会自动切到HSI上(维持系统不挂掉, 但是系统运行速度会大大降低)。那为啥要手工切到片内晶振上呢?
