已知 #define USART_IT_TXE ((uint16_t)0x0727)
在函数USART_GetITStatus中
usartreg = (((uint8_t)USART_IT) >> 0x05);
后下面开始判断 问题在于0x0727右移五位不可能等于以下任一，我不太明白此函数运行的原理
if (usartreg == 0x01)
{
itmask &= USARTx->CR1;
}
else if (usartreg == 0x02)
{
itmask &= USARTx->CR2;
}
else
{
itmask &= USARTx->CR3;
}
完整代码如下：
ITStatus USART_GetITStatus(USART_TypeDef* USARTx, uint16_t USART_IT)
{
uint32_t bitpos = 0x00, itmask = 0x00, usartreg = 0x00;
ITStatus bitstatus = RESET;
assert_param(IS_USART_ALL_PERIPH(USARTx));
assert_param(IS_USART_GET_IT(USART_IT));
if (USART_IT == USART_IT_CTS)
{
assert_param(IS_USART_123_PERIPH(USARTx));
}
usartreg = (((uint8_t)USART_IT) >> 0x05); //D5~D7：代表中断标志位对应的中断使能位在 CR1、CR2还是CR3寄存器中
itmask = USART_IT & IT_Mask;
itmask = (uint32_t)0x01 << itmask; //D0~D4：代表中断标志位对应的中断使能位在CRx寄存器的哪一位
if (usartreg == 0x01)
{
itmask &= USARTx->CR1;
}
else if (usartreg == 0x02)
{
itmask &= USARTx->CR2;
}
else
{
itmask &= USARTx->CR3;
}
bitpos = USART_IT >> 0x08; //D8~D15：代表中断标志位在SR寄存器中的哪一位
bitpos = (uint32_t)0x01 << bitpos;
bitpos &= USARTx->SR;
if ((itmask != (uint16_t)RESET)&&(bitpos != (uint16_t)RESET))
{
bitstatus = SET;
}
else
{
bitstatus = RESET;
}
return bitstatus;
}
