int fputc(int ch, FILE *p) { while((USART1->SR & 0x40)==0); USART1->DR=ch; return ch; }作用

& 0x80) == 0); USART1->DR = (ch & 0xFF); return ch; }

This is a function that writes a single character (represented by the integer "ch") to a file (represented by the pointer "p") using USART1 (a Universal Synchronous/Asynchronous Receiver/Transmitter).

The function first checks the status register (SR) of USART1 to see if it is ready to transmit data. It does this by checking if the transmit data register is empty (the 7th bit of the SR is set to 1).

If the transmit data register is not empty, the function waits in a loop until it is (by repeatedly checking the SR). Once the transmit data register is empty, the function writes the character to the data register (DR) of USART1, which is then transmitted over the UART.

Finally, the function returns the character that was written to the file.