STM32 study notes - AFIO clock configuration issues

Recently, when I was writing a program, I found that there was a problem with setting the external interrupt. Why did the previous program not work? After a night of tossing and turning, I found that the problem was in the configuration of the AFIO clock. I did not enable the AFIO clock.

When should AFIO be enabled? Reference Manual: 

It is very clear that the three types of registers of AFIO need to be turned on when operating: 
1. Event control register (AFIO_EVCR)
2. Multiplexing remapping and debugging I/O configuration register (AFIO_MAPR)
3. External interrupt configuration register x (AFIO_EXTICRx)
These three types are actually all the registers of AFIO, AFIO_EVCR is related to events, AFIO_MAPR is related to remapping and debugging I/O, and AFIO_EXTICRx is related to external interrupts. Therefore, AFIO needs to be turned on when remapping and debugging I/O configuration, external interrupts, and events.

Looking back at the previous program, you can understand it. In the previous program, there are two lines of code in the initialization area of ​​my main function:

RCC->APB2ENR |= 0x00000001; //Disable JTAG, enable SWD

AFIO->MAPR = (0x00FFFFFF & AFIO->MAPR)|0x02000000;   

This code configures the JTAG and SWD pins, and also configures the AFIO clock. So the function can be realized without operating AFIO in the subsequent external interrupt configuration code. Finally, I added this sentence to the program, and the problem was solved perfectly. RCC_APB2PeriphClockCmd(RCC_APB2Periph_AFIO,ENABLE);