接上文，继续来看这个函数：

/*** @brief  Initializes the GPIOx peripheral according to the specified*         parameters in the GPIO_InitStruct.* @param  GPIOx: where x can be (A..G) to select the GPIO peripheral.* @param  GPIO_InitStruct: pointer to a GPIO_InitTypeDef structure that*         contains the configuration information for the specified GPIO peripheral.* @retval None*/
void GPIO_Init(GPIO_TypeDef* GPIOx, GPIO_InitTypeDef* GPIO_InitStruct)
{uint32_t currentmode = 0x00, currentpin = 0x00, pinpos = 0x00, pos = 0x00;uint32_t tmpreg = 0x00, pinmask = 0x00;/* Check the parameters */assert_param(IS_GPIO_ALL_PERIPH(GPIOx));assert_param(IS_GPIO_MODE(GPIO_InitStruct->GPIO_Mode));assert_param(IS_GPIO_PIN(GPIO_InitStruct->GPIO_Pin));  /*---------------------------- GPIO Mode Configuration -----------------------*/currentmode = ((uint32_t)GPIO_InitStruct->GPIO_Mode) & ((uint32_t)0x0F);if ((((uint32_t)GPIO_InitStruct->GPIO_Mode) & ((uint32_t)0x10)) != 0x00){ /* Check the parameters */assert_param(IS_GPIO_SPEED(GPIO_InitStruct->GPIO_Speed));/* Output mode */currentmode |= (uint32_t)GPIO_InitStruct->GPIO_Speed;}
/*---------------------------- GPIO CRL Configuration ------------------------*//* Configure the eight low port pins */if (((uint32_t)GPIO_InitStruct->GPIO_Pin & ((uint32_t)0x00FF)) != 0x00){tmpreg = GPIOx->CRL;for (pinpos = 0x00; pinpos < 0x08; pinpos++){pos = ((uint32_t)0x01) << pinpos;/* Get the port pins position */currentpin = (GPIO_InitStruct->GPIO_Pin) & pos;if (currentpin == pos){pos = pinpos << 2;/* Clear the corresponding low control register bits */pinmask = ((uint32_t)0x0F) << pos;tmpreg &= ~pinmask;/* Write the mode configuration in the corresponding bits */tmpreg |= (currentmode << pos);/* Reset the corresponding ODR bit */if (GPIO_InitStruct->GPIO_Mode == GPIO_Mode_IPD){GPIOx->BRR = (((uint32_t)0x01) << pinpos);}else{/* Set the corresponding ODR bit */if (GPIO_InitStruct->GPIO_Mode == GPIO_Mode_IPU){GPIOx->BSRR = (((uint32_t)0x01) << pinpos);}}}}GPIOx->CRL = tmpreg;}

一段一段来看：

/**
  * @brief  Initializes the GPIOx peripheral according to the specified
  *         parameters in the GPIO_InitStruct.
  * @param  GPIOx: where x can be (A..G) to select the GPIO peripheral.
  * @param  GPIO_InitStruct: pointer to a GPIO_InitTypeDef structure that
  *         contains the configuration information for the specified GPIO peripheral.
  * @retval None
  */

这个函数的功能是：按照在GPIO结初始化结构体的里的参数，来初始化GPIO

输入参数有两个。没有返回值。

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  /* Check the parameters */
  assert_param(IS_GPIO_ALL_PERIPH(GPIOx));
  assert_param(IS_GPIO_MODE(GPIO_InitStruct->GPIO_Mode));
  assert_param(IS_GPIO_PIN(GPIO_InitStruct->GPIO_Pin));  

第一句：  assert_param(IS_GPIO_ALL_PERIPH(GPIOx));（第二句和第三句作用也类似，）

这是使用 assert_param（）函数来检查传进来的GPIOx是否在IS_GPIO_ALL_PERIPH这个宏定义范围之内。

也就是检查传进来的参数是否有效。也就是传来进的只能是这里定义的这些。

其中的->相当于GPIO_InitStruct.GPIO_Mode，就是取出这个结构体中的该成员变量的值的意思。

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后面的

/*---------------------------- GPIO Mode Configuration -----------------------*/

/*---------------------------- GPIO CRL Configuration ------------------------*/

很明显，就是根据收到的端口以及端口的引脚，输入输出模式以及工作速度，配置好相应的寄存器，没必要仔细看了。