STM32中GPIO的配置風(fēng)格和以往研究的MCU有很大的不同，研究了好一段時間才搞通。

typedef enum
{ GPIO_Mode_AIN = 0x0,
GPIO_Mode_IN_FLOATING = 0x04,
GPIO_Mode_IPD = 0x28,
GPIO_Mode_IPU = 0x48,
GPIO_Mode_Out_OD = 0x14,
GPIO_Mode_Out_PP = 0x10,
GPIO_Mode_AF_OD = 0x1C,
GPIO_Mode_AF_PP = 0x18
}GPIOMode_TypeDef;

配置一個引腳只需要4位寄存器，而上面卻定義了8位，仔細(xì)研究GPIO_Init（）函數(shù)后，確定為ST開發(fā)人員加上去的標(biāo)識位。0x1_ 的是輸出標(biāo)識，其他則為輸入模式。

下面看一下GPIO_Init（）這個函數(shù)：

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);//屏蔽高半個字節(jié)的標(biāo)識位
if ((((uint32_t)GPIO_InitStruct->GPIO_Mode) & ((uint32_t)0x10)) != 0x00)//判斷是否為輸出，0x1_
{
/* Check the parameters
assert_param(IS_GPIO_SPEED(GPIO_InitStruct->GPIO_Speed));
/* Output mode
currentmode |= (uint32_t)GPIO_InitStruct->GPIO_Speed;//如果是輸出，則加上相關(guān)的速度標(biāo)志
}
/*---------------------------- GPIO CRL Configuration ------------------------
/* Configure the eight low port pins
if (((uint32_t)GPIO_InitStruct->GPIO_Pin & ((uint32_t)0x00FF)) != 0x00)//判斷引腳是否有效
{
tmpreg = GPIOx->CRL;//讀出CRL寄存器中的值，并保存
for (pinpos = 0x00; pinpos < 0x08; pinpos++)
{
pos = ((uint32_t)0x01) << pinpos;
/* Get the port pins position找出引腳的位置
currentpin = (GPIO_InitStruct->GPIO_Pin) & pos;
if (currentpin == pos)
{
pos = pinpos << 2;//pos*4,因為每個引腳配置占4位
/* Clear the corresponding low control register bits
pinmask = ((uint32_t)0x0F) << pos;
tmpreg &= ~pinmask;//把需要配置引腳的4位清0，其位不變
/* Write the mode configuration in the corresponding bits
tmpreg |= (currentmode << pos);//把配置數(shù)據(jù)寫入tmpreg
/* Reset the corresponding ODR bit//如果是下拉輸入或者上拉輸入，則還需要配置PxODR位
if (GPIO_InitStruct->GPIO_Mode == GPIO_Mode_IPD)
{
GPIOx->BRR = (((uint32_t)0x01) << pinpos);//如果下拉，清除對應(yīng)ODRy為0
}
else
{
/* Set the corresponding ODR bit
if (GPIO_InitStruct->GPIO_Mode == GPIO_Mode_IPU)
{
GPIOx->BSRR = (((uint32_t)0x01) << pinpos);//如果上拉，設(shè)置對應(yīng)的ODRy為1
}
}
}
}
GPIOx->CRL = tmpreg;//把配置好的數(shù)值寫入寄存器
}