STM32F4系列GPIO配置

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在stm32系列单片机的学习过程中，大部分人是从f1系列开始，今天第一次接触到f4系列的配置问题，所以写这篇博客进行简单的解释

GPIO的基本结构见STM32学习笔记，f1系列和f4系列在结构上并无区别，只是在代码配置中有所区别

首先先看看在f1系列里面对GPIO的使能：

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/*开启时钟*/
	RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);			//开启GPIOA的时钟
	
	/*GPIO初始化*/
	GPIO_InitTypeDef GPIO_InitStructure;
	GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
	GPIO_InitStructure.GPIO_Pin = GPIO_Pin_2;
	GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
	GPIO_Init(GPIOA, &GPIO_InitStructure);							//将PA2引脚初始化为复用推挽输出	
//受外设控制的引脚，均需要配置为复用模式

这里演示的是把PA2脚使能为推挽输出

我们可以将使能分为这么几步：

  1. 打开时钟
  2. 初始化GPIO
  3. Init函数完成初始化

f4系列的初始化的大致步骤也是类似：

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   RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA,ENABLE);

GPIO_InitTypeDef Serial_Structure;
Serial_Structure.GPIO_Mode = GPIO_Mode_AF;
Serial_Structure.GPIO_Pin = GPIO_Pin_9;
Serial_Structure.GPIO_Speed = GPIO_Speed_50MHz;
Serial_Structure.GPIO_OType = GPIO_OType_PP;
Serial_Structure.GPIO_PuPd = GPIO_PuPd_UP;
GPIO_Init(GPIOA, &Serial_Structure);

这里演示的是把PA9使能为推挽输出

可以注意到的是，两个GPIO使能的代码有细微的差别，比如：
f1中的时钟开启函数是：RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);，而f4是：RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA,ENABLE);
f4的初始化结构体比f1多OType和PuPd需要配置

这些区别可以在各自的固件库文件中的stm32f4xx_gpio.c/h和stm32f1xx_gpio.c/h文件中找到

这边只给出f4系列配置的过程

在固件库每一个.c文件的开头都会有一段解释对应用法的说明

f4 GPIO文件讲解

stm32f4xx_gpio.c前面给出的说明：

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/**
  ******************************************************************************
  * @file    stm32f4xx_gpio.c
  * @author  MCD Application Team
  * @version V1.8.0
  * @date    04-November-2016
  * @brief   This file provides firmware functions to manage the following 
  *          functionalities of the GPIO peripheral:           
  *           + Initialization and Configuration
  *           + GPIO Read and Write
  *           + GPIO Alternate functions configuration
  * 
@verbatim  
 ===============================================================================
                      ##### How to use this driver #####
 ===============================================================================       
 [..]             
   (#) Enable the GPIO AHB clock using the following function
       RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOx, ENABLE);
               
   (#) Configure the GPIO pin(s) using GPIO_Init()
       Four possible configuration are available for each pin:
       (++) Input: Floating, Pull-up, Pull-down.
       (++) Output: Push-Pull (Pull-up, Pull-down or no Pull)
            Open Drain (Pull-up, Pull-down or no Pull). In output mode, the speed 
            is configurable: 2 MHz, 25 MHz, 50 MHz or 100 MHz.
       (++) Alternate Function: Push-Pull (Pull-up, Pull-down or no Pull) Open 
            Drain (Pull-up, Pull-down or no Pull).
       (++) Analog: required mode when a pin is to be used as ADC channel or DAC 
            output.
   
   (#) Peripherals alternate function:
       (++) For ADC and DAC, configure the desired pin in analog mode using 
            GPIO_InitStruct->GPIO_Mode = GPIO_Mode_AN;
            (+++) For other peripherals (TIM, USART...):
            (+++) Connect the pin to the desired peripherals' Alternate 
                     Function (AF) using GPIO_PinAFConfig() function
            (+++) Configure the desired pin in alternate function mode using
                     GPIO_InitStruct->GPIO_Mode = GPIO_Mode_AF
            (+++) Select the type, pull-up/pull-down and output speed via 
                     GPIO_PuPd, GPIO_OType and GPIO_Speed members
            (+++) Call GPIO_Init() function
          
   (#) To get the level of a pin configured in input mode use GPIO_ReadInputDataBit()
            
   (#) To set/reset the level of a pin configured in output mode use 
       GPIO_SetBits()/GPIO_ResetBits()
                 
   (#) During and just after reset, the alternate functions are not 
       active and the GPIO pins are configured in input floating mode (except JTAG
       pins).
  
   (#) The LSE oscillator pins OSC32_IN and OSC32_OUT can be used as general purpose 
       (PC14 and PC15, respectively) when the LSE oscillator is off. The LSE has 
       priority over the GPIO function.
  
   (#) The HSE oscillator pins OSC_IN/OSC_OUT can be used as 
       general purpose PH0 and PH1, respectively, when the HSE oscillator is off. 
       The HSE has priority over the GPIO function.
               
@endverbatim        
  *
  ******************************************************************************
  * @attention
  *
  * <h2><center>&copy; COPYRIGHT 2016 STMicroelectronics</center></h2>
  *
  * Licensed under MCD-ST Liberty SW License Agreement V2, (the "License");
  * You may not use this file except in compliance with the License.
  * You may obtain a copy of the License at:
  *
  *        http://www.st.com/software_license_agreement_liberty_v2
  *
  * Unless required by applicable law or agreed to in writing, software 
  * distributed under the License is distributed on an "AS IS" BASIS, 
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  *
  ******************************************************************************
  */

通过阅读这段说明我们可以知道如何使用这个文件里面的函数
当然这篇博客只涉及GPIO的初始化过程，所以我们只会讲解其中一部分，剩余可以自行去了解

从 ##### How to use this driver ##### 后面开始就是正式的讲解
这里我们只说明前面两段，这两段的内容足够我们完成GPIO的见到那配置

第一段：

Enable the GPIO AHB clock using the following function
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOx, ENABLE);

即使用RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOx, ENABLE);语句来进行时钟使能

第二段：

Configure the GPIO pin(s) using GPIO_Init()
Four possible configuration are available for each pin:
(++) Input: Floating, Pull-up, Pull-down.
(++) Output: Push-Pull (Pull-up, Pull-down or no Pull)
Open Drain (Pull-up, Pull-down or no Pull). In output mode, the speed
is configurable: 2 MHz, 25 MHz, 50 MHz or 100 MHz.
(++) Alternate Function: Push-Pull (Pull-up, Pull-down or no Pull) Open
Drain (Pull-up, Pull-down or no Pull).
(++) Analog: required mode when a pin is to be used as ADC channel or DAC
output.

这段讲解了结构体的配置，你需要确定的有：

  1. 你使用的引脚
  2. 你选择的模式
  3. 你选择的传输速度

文档里同时也说明了模式有哪些:

  1. 输入
  2. 输出
  3. 复用
  4. 模拟

其中输入模式分为

  1. 悬空
  2. 上拉
  3. 下拉

输出分为：

  1. 推挽
  2. 开漏

复用需要同时设置输入和输出的两种

具体到代码：

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RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA,ENABLE); //开启时钟
	
	GPIO_InitTypeDef Serial_Structure; //初始化结构体
	Serial_Structure.GPIO_Mode = GPIO_Mode_AF; //选择模式
	Serial_Structure.GPIO_Pin = GPIO_Pin_9; //选择引脚
	Serial_Structure.GPIO_Speed = GPIO_Speed_50MHz; //选择速度
	Serial_Structure.GPIO_OType = GPIO_OType_PP; //选择输出模式
	Serial_Structure.GPIO_PuPd = GPIO_PuPd_UP; //选择输入模式
	GPIO_Init(GPIOA, &Serial_Structure); //完成初始化

总结

两个系列GPIO的初始化结构相同，只有细微区别，在使用前可以打开对应文件阅读说明，便于更好的理解和使用对应的函数

给穷逼一点钱吧！
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