概述

    本篇文章介绍如何使用STM32HAL库，USART-调试串口（大小端测试）示例。

硬件：STM32F103CBT6最小系统板
软件：Keil 5.29  + STM32CubeMX6.01
 

一、原理

          CPU的大端和小端模式很多地方都会用到，由于不同硬件商，按自己的构想设计硬件，导致了硬件设计不同，工作原理也有差异。之所以就会有大小端这个说法。
 大小端模式：
    大端模式，是指数据的高字节保存在内存的低地址中，而数据的低字节保存在内存的高地址中，这样的存储模式有点儿类似于把数据当作字符串顺序处理：地址由小向大增加，而数据从高位往低位放；这和我们的阅读习惯一致。

    小端模式，是指数据的高字节保存在内存的高地址中，而数据的低字节保存在内存的低地址中，这种存储模式将地址的高低和数据位权有效地结合起来，高地址部分权值高，低地址部分权值低。

下面以unsigned int value = 0x12345678为例，分别看看在两种字节序下其存储情况，我们可以用unsigned char buf[4]来表示value

Big-Endian: 低地址存放高位，如下：

高地址
　　---------------
　　buf[3] (0x78) -- 低位
　　buf[2] (0x56)
　　buf[1] (0x34)
　　buf[0] (0x12) -- 高位
　　---------------
　　低地址

Little-Endian: 低地址存放低位，如下：

高地址
　　---------------
　　buf[3] (0x12) -- 高位
　　buf[2] (0x34)
　　buf[1] (0x56)
　　buf[0] (0x78) -- 低位
　　--------------

低地址

比如：
要存放的数据：0x22334455
低字节为:0x22
高字节为:0x55
 

小端模式：
内存中存放顺序：0x22,0x33,0x44,0x55
读取数据方向：从高地址开始读取数据
读取结果：0x55,0x44,0x33,0x22

大端模式：
内存中排存放序:0x55,0x44,0x33,0x22
读取数据方向：从低地址开始读取数据
读取结果：0x55,0x44,0x33,0x22

二、STM32CubeMx配置

三、Examples

main.c文件

/* USER CODE BEGIN Header */
/**
  ******************************************************************************
  * @file           : main.c
  * @brief          : Main program body
  ******************************************************************************
  * @attention
  *
  * <h2><center>&copy; Copyright (c) 2021 STMicroelectronics.
  * All rights reserved.</center></h2>
  *
  * This software component is licensed by ST under BSD 3-Clause license,
  * the "License"; You may not use this file except in compliance with the
  * License. You may obtain a copy of the License at:
  *                        opensource.org/licenses/BSD-3-Clause
  *
  ******************************************************************************
  */
/* USER CODE END Header */
/* Includes ------------------------------------------------------------------*/
#include "main.h"
#include "usart.h"
#include "gpio.h"

/* Private includes ----------------------------------------------------------*/
/* USER CODE BEGIN Includes */
#include "stdio.h"
#include "string.h"
/* USER CODE END Includes */

/* Private typedef -----------------------------------------------------------*/
/* USER CODE BEGIN PTD */

/* USER CODE END PTD */

/* Private define ------------------------------------------------------------*/
/* USER CODE BEGIN PD */
/* USER CODE END PD */

/* Private macro -------------------------------------------------------------*/
/* USER CODE BEGIN PM */

/* USER CODE END PM */

/* Private variables ---------------------------------------------------------*/

/* USER CODE BEGIN PV */

/* USER CODE END PV */

/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
/* USER CODE BEGIN PFP */

/* USER CODE END PFP */

/* Private user code ---------------------------------------------------------*/
/* USER CODE BEGIN 0 */
#ifdef __GNUC__
  /* With GCC/RAISONANCE, small printf (option LD Linker->Libraries->Small printf
     set to 'Yes') calls __io_putchar() */
  #define PUTCHAR_PROTOTYPE int __io_putchar(int ch)
#else
  #define PUTCHAR_PROTOTYPE int fputc(int ch, FILE *f)
#endif /* __GNUC__ */
/**
  * @brief  Retargets the C library printf function to the USART.
  * @param  None
  * @retval None
  */
PUTCHAR_PROTOTYPE
{
  /* Place your implementation of fputc here */
  /* e.g. write a character to the EVAL_COM1 and Loop until the end of transmission */
  HAL_UART_Transmit(&huart1, (uint8_t *)&ch, 1, 0xFFFF);
 
  return ch;
}
 
int fgetc(FILE * f)
{
  uint8_t ch = 0;
  HAL_UART_Receive(&huart1, (uint8_t *)&ch, 1, 0xffff);
  return ch;
}


typedef union
{
 	int a;
 	char b;
}union_t;


void union_test(void)
{
	union_t ut;  //共用体测试
  ut.a = 0x22334455;
	
	printf("*************共用体方式测试*************\r\n");
  if(ut.b==0x22)
    printf(">> 编译环境为大端模式\n");
  if(ut.b==0x55)
    printf(">> 编译环境为小端模式\n"); 
	else
    printf(">> 程序运行出错\n");
}

void pointer_test(void)
{
	uint8_t ch;
  uint8_t i,	data[8];
  uint32_t data_32 = 0x22334455;
	
	printf("*************指针方式测试*************\r\n");
	memcpy(data,&data_32,sizeof(uint32_t));
  for(i=0;i<sizeof(uint32_t);++i)
  {
    printf("data[[%d]=0x%X\n",i,data[i]);
  }
  if(data[0]==(data_32&0x000000FF))
    printf(">> 编译环境为小端模式\n");
   else if(data[0]==(data_32&0xFF000000))
    printf(">> 编译环境为大端模式\n");
   else
    printf(">> 程序运行出错\n");
}

/* USER CODE END 0 */

/**
  * @brief  The application entry point.
  * @retval int
  */
int main(void)
{
  /* USER CODE BEGIN 1 */
	
  /* USER CODE END 1 */

  /* MCU Configuration--------------------------------------------------------*/

  /* Reset of all peripherals, Initializes the Flash interface and the Systick. */
  HAL_Init();

  /* USER CODE BEGIN Init */

  /* USER CODE END Init */

  /* Configure the system clock */
  SystemClock_Config();

  /* USER CODE BEGIN SysInit */

  /* USER CODE END SysInit */

  /* Initialize all configured peripherals */
  MX_GPIO_Init();
  MX_USART1_UART_Init();
  /* USER CODE BEGIN 2 */
	printf("HeiHei!!!\n");
	 
	union_test();
	pointer_test();
  /* USER CODE END 2 */

  /* Infinite loop */
  /* USER CODE BEGIN WHILE */
  while (1)
  {
		HAL_Delay(1000);
		HAL_GPIO_TogglePin(LED_GPIO_Port, LED_Pin);
    /* USER CODE END WHILE */

    /* USER CODE BEGIN 3 */
  }
  /* USER CODE END 3 */
}

/**
  * @brief System Clock Configuration
  * @retval None
  */
void SystemClock_Config(void)
{
  RCC_OscInitTypeDef RCC_OscInitStruct = {0};
  RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};

  /** 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.HSEPredivValue = RCC_HSE_PREDIV_DIV1;
  RCC_OscInitStruct.HSIState = RCC_HSI_ON;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
  RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
  RCC_OscInitStruct.PLL.PLLMUL = RCC_PLL_MUL9;
  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_DIV2;
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;

  if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_2) != HAL_OK)
  {
    Error_Handler();
  }
}

/* USER CODE BEGIN 4 */

/* USER CODE END 4 */

/**
  * @brief  This function is executed in case of error occurrence.
  * @retval None
  */
void Error_Handler(void)
{
  /* USER CODE BEGIN Error_Handler_Debug */
  /* User can add his own implementation to report the HAL error return state */

  /* USER CODE END Error_Handler_Debug */
}

#ifdef  USE_FULL_ASSERT
/**
  * @brief  Reports the name of the source file and the source line number
  *         where the assert_param error has occurred.
  * @param  file: pointer to the source file name
  * @param  line: assert_param error line source number
  * @retval None
  */
void assert_failed(uint8_t *file, uint32_t line)
{
  /* USER CODE BEGIN 6 */
  /* User can add his own implementation to report the file name and line number,
     tex: printf("Wrong parameters value: file %s on line %d\r\n", file, line) */
  /* USER CODE END 6 */
}
#endif /* USE_FULL_ASSERT */

/************************ (C) COPYRIGHT STMicroelectronics *****END OF FILE****/

四、运行结果

传送门->代码

五、总结

      好了，就介绍到此。