Interrupt processing

The whole process of interrupt refers to the process starting from the interrupt request sent by the interrupt source ,CPU In response to this request , The current program was interrupted , Go to interrupt service program , Until the interrupt service program is executed ,CPU Return to the original program and continue the whole process .

step

1. Request interrupt → In response to interrupt → Turn off interrupt
2. Keep breakpoints
3. Bring out interrupt service program
4. Protection site
5. Open interrupt
6. Execute interrupt service procedure
7. Turn off interrupt
8. Restore the scene
9. Turn on interrupt
10. Interrupt return

 2. Save breakpoints ： Ensure that after the interrupt program is executed, it can return to continue to execute the following program , In fact, the program counter is saved

3. Bring out interrupt service program ： In fact, it is to read the address of the program we want to execute , In order to carry out

4. Save the scene ： Save the data in the register , So that the data can be recovered when it is executed . In order that the interrupt handler does not destroy the contents of the register in the main program , The contents of each register at the breakpoint shall be pushed into the stack for protection , Re entry interrupt processing .

On interrupt and off interrupt ： Lock

• take CPU Do not respond to higher level interrupt requests

• When entering the interrupt service program , CPU Ben has been automatically disabled CPU Interrupt response on , because CPU It cannot be assumed that an interrupt service routine is reentrant .

• If it is interrupted while saving the register value , Then another operation is likely to rewrite the register , Site cannot be recovered

10. Interrupt return

An interrupt return instruction shall be arranged at the end of the interrupt service subroutine IRET, Execute the command , The system automatically saves the stored in the stack IP/EIP and CS Value pop-up , So as to restore the address value at the breakpoint of the main program , It also automatically restores the flag register FR or EFR The content of , send CPU Go to the interrupted program to continue execution