【转】STM32库函数中GPIO_Init的理解

只看该作者 · 2018-7-26 21:30

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;
配置一个引脚只需要4位寄存器，而上面却定义了8位，仔细研究GPIO_Init（）函数后，确定为ST开发人员加上去的标识位。0x1_ 的是输出标识，其他则为输入模式。
下面看一下GPIO_Init（）这个函数：
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);//屏蔽高半个字节的标识位
if ((((uint32_t)GPIO_InitStruct->GPIO_Mode) & ((uint32_t)0x10)) != 0x00)//判断是否为输出，0x1_
{
/* Check the parameters
assert_param(IS_GPIO_SPEED(GPIO_InitStruct->GPIO_Speed));
/* Output mode
currentmode |= (uint32_t)GPIO_InitStruct->GPIO_Speed;//如果是输出，则加上相关的速度标志
}
/*---------------------------- GPIO CRL Configuration ------------------------
/* Configure the eight low port pins
if (((uint32_t)GPIO_InitStruct->GPIO_Pin & ((uint32_t)0x00FF)) != 0x00)//判断引脚是否有效
{
tmpreg = GPIOx->CRL; //读出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 找出引脚的位置
currentpin = (GPIO_InitStruct->GPIO_Pin) & pos;
if (currentpin == pos)
{
pos = pinpos << 2; //pos*4,因为每个引脚配置占4位
/* Clear the corresponding low control register bits
pinmask = ((uint32_t)0x0F) << pos;
tmpreg &= ~pinmask; //把需要配置引脚的4位清0，其位不变
/* Write the mode configuration in the corresponding bits
tmpreg |= (currentmode << pos); //把配置数据写入tmpreg
/* Reset the corresponding ODR bit //如果是下拉输入或者上拉输入，则还需要配置PxODR位
if (GPIO_InitStruct->GPIO_Mode == GPIO_Mode_IPD)
{
GPIOx->BRR = (((uint32_t)0x01) << pinpos); //如果下拉，清除对应ODRy为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，设置对应的ODRy为1
}
}
}
}
GPIOx->CRL = tmpreg; //把配置好的数值写入寄存器
}