RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSI_DIV2;

这段代码是什么意思？

这段代码是用来配置STM32芯片的时钟源的。其中，RCC代表Reset and Clock Control，而PLL代表Phase-Locked Loop，是一种用来产生稳定高频时钟信号的电路。

在这段代码中，RCC_OscInitStruct.PLL.PLLSource的值被设置为RCC_PLLSOURCE_HSI_DIV2，表示使用内部高速时钟源（HSI）除以2作为PLL的输入时钟源。这个PLL的输出时钟信号会用来驱动STM32芯片的各个模块，例如CPU、外设等。

相关问题

修改以下程序，使其接收指令后发送一个hello,world字符串。#include "main.h"#include "usart.h"#include "gpio.h"#include "stdio.h"#include "string.h"uint8_t aRxBuffer;void SystemClock_Config(void);int fputc(int ch, FILE *f){ uint8_t temp[1] = {ch}; HAL_UART_Transmit(&huart1, temp, 1, 0xffff);return ch;}int fgetc(FILE * f){ uint8_t ch = 0; HAL_UART_Receive(&huart1,&ch, 1, 0xffff); return ch;}int main(void){ HAL_Init(); SystemClock_Config(); MX_GPIO_Init(); MX_USART1_UART_Init(); /* USER CODE BEGIN 2 */ HAL_UART_Receive_IT(&huart1, (uint8_t *)&aRxBuffer, 1); user_main_printf(""); /* USER CODE END 2 */ while (1) { }}void SystemClock_Config(void){ RCC_OscInitTypeDef RCC_OscInitStruct = {0}; RCC_ClkInitTypeDef RCC_ClkInitStruct = {0}; RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI; RCC_OscInitStruct.HSIState = RCC_HSI_ON; RCC_OscInitStruct.HSICalibrationValue = RCC_HSICALIBRATION_DEFAULT; RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON; RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSI_DIV2; RCC_OscInitStruct.PLL.PLLMUL = RCC_PLL_MUL2; if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK) { Error_Handler(); } 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_DIV2; RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1; if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_0) != HAL_OK) { Error_Handler(); }}void HAL_UART_RxCpltCallback(UART_HandleTypeDef *huart){ char *pCmd = NULL; uint8_t len; switch(aRxBuffer){ case '1': pCmd = "command 1\r\n"; len = strlen(pCmd); break; case '2': pCmd = "command 2\r\n"; len = strlen(pCmd); break; case '3': pCmd = "command 3\r\n"; len = strlen(pCmd); break; case '4': pCmd = "command 4\r\n"; len = strlen(pCmd); break; default: pCmd = "command cmd\r\n"; len = strlen(pCmd); break; } HAL_UART_Transmit(&huart1, (uint8_t *)pCmd, len,0xFFFF); HAL_UART_Receive_IT(&huart1, (uint8_t *)&aRxBuffer, 1); }void Error_Handler(void){}#ifdef USE_FULL_ASSERTvoid assert_failed(uint8_t *file, uint32_t line){ }#endif

请修改程序如下：

#include "main.h"
#include "usart.h"
#include "gpio.h"
#include "stdio.h"
#include "string.h"

uint8_t aRxBuffer;

void SystemClock_Config(void);

int fputc(int ch, FILE *f) {
    uint8_t temp[1] = {ch};
    HAL_UART_Transmit(&huart1, temp, 1, 0xffff);
    return ch;
}

int fgetc(FILE * f) {
    uint8_t ch = 0;
    HAL_UART_Receive(&huart1,&ch, 1, 0xffff);
    return ch;
}

int main(void) {
    HAL_Init();
    SystemClock_Config();
    MX_GPIO_Init();
    MX_USART1_UART_Init();

    HAL_UART_Receive_IT(&huart1, (uint8_t *)&aRxBuffer, 1);

    while (1) {
        if (aRxBuffer != 0) {
            HAL_UART_Transmit(&huart1, "hello, world\r\n", 14, 0xFFFF);
            aRxBuffer = 0;
            HAL_UART_Receive_IT(&huart1, (uint8_t *)&aRxBuffer, 1);
        }
    }
}

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

    RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI;
    RCC_OscInitStruct.HSIState = RCC_HSI_ON;
    RCC_OscInitStruct.HSICalibrationValue = RCC_HSICALIBRATION_DEFAULT;
    RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
    RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSI_DIV2;
    RCC_OscInitStruct.PLL.PLLMUL = RCC_PLL_MUL2;

    if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK) {
        Error_Handler();
    }

    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_DIV2;
    RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;

    if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_0) != HAL_OK) {
        Error_Handler();
    }
}

void Error_Handler(void) {}

#ifdef  USE_FULL_ASSERT
void assert_failed(uint8_t *file, uint32_t line) {}
#endif

修改后的程序会在收到任何字符后发送 "hello, world" 字符串，然后再继续等待下一个字符。

/** * @brief System Clock Configuration * @retval None */ void SystemClock_Config(void) { RCC_OscInitTypeDef RCC_OscInitStruct = {0};//定义结构体变量RCC_OscInitStruct RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};//定义结构体变量RCC_ClkInitStruct RCC_PeriphCLKInitTypeDef PeriphClkInit = {0};//定义结构体变量PeriphClkInit /** Initializes the CPU, AHB and APB busses clocks */ RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_LSI|RCC_OSCILLATORTYPE_HSE; RCC_OscInitStruct.HSEState = RCC_HSE_BYPASS; RCC_OscInitStruct.HSEPredivValue = RCC_HSE_PREDIV_DIV2; RCC_OscInitStruct.HSIState = RCC_HSI_ON; RCC_OscInitStruct.LSIState = RCC_LSI_ON; RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON; RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE; RCC_OscInitStruct.PLL.PLLMUL = RCC_PLL_MUL12; if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK) { Error_Handler(); } /** Initializes the CPU, AHB and APB busses 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_DIV2; RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1; if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_2) != HAL_OK) { Error_Handler(); } PeriphClkInit.PeriphClockSelection = RCC_PERIPHCLK_ADC; PeriphClkInit.AdcClockSelection = RCC_ADCPCLK2_DIV6; if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInit) != HAL_OK) { Error_Handler(); } }

SystemClock_Config函数是用来配置系统时钟的。它执行了以下操作：

1. 初始化CPU、AHB和APB总线时钟。

2. 配置振荡器类型：使用LSI和HSE两种振荡器。

3. 配置HSE状态为旁路模式（BYPASS）。

4. 配置HSE预分频值为2。

5. 配置HSI状态为开启。

6. 配置LSI状态为开启。

7. 配置PLL状态为开启。

8. 配置PLL时钟源为HSE。

9. 配置PLL倍频因子为12。

10. 调用HAL_RCC_OscConfig函数配置时钟，并检查返回值是否为HAL_OK，如果不是则调用Error_Handler函数进行错误处理。

11. 初始化CPU、AHB和APB总线时钟。

12. 配置系统时钟源为PLL时钟。

13. 配置AHB时钟分频系数为1。

14. 配置APB1时钟分频系数为2。

15. 配置APB2时钟分频系数为1。

16. 调用HAL_RCC_ClockConfig函数配置时钟，并检查返回值是否为HAL_OK，如果不是则调用Error_Handler函数进行错误处理。

17. 配置外设时钟：配置ADC外设时钟分频系数为6。

18. 调用HAL_RCCEx_PeriphCLKConfig函数配置外设时钟，并检查返回值是否为HAL_OK，如果不是则调用Error_Handler函数进行错误处理。

这个函数的作用是根据具体的系统需求配置系统时钟，确保各个外设能够正常工作。