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详细说明： Using Interrupts Version 1.0 Disclaimer : While every effort has been made to make sure the information in this document is correct, the author can not be liable for any damages whatsoever for loss relating to this document. Use this information at your own risk. Table of Contents What are Interrupts? Page 2 Interrupts and Intel Arc hitecture Page 3 Hardware Interrupts Page 3 Implementing the Interrupt Service Routine (ISR) Page 5 Using your new Interrupt Service Routine Page 6 The Programmable Interrupt Controller Page 7 IRQ2/IRQ9 Redirection Page 9 Programmable Interrupt Controllers Addresses Page 10 Initialization Command Word 1 (ICW1) Page 11 Initialization Command Word 2 (ICW2) Page 12 Initialization Command Word 3 (ICW3) Page 12 Initialization Command Word 4 (ICW4) Page 14 Operation Control Word 1 (OCW1) Page 15 Operation Control Word 2 (OCW2) Page 16 Operation Control Word 3 (OCW3) Page 17 Using Interrupts http://www.senet.com.au/~cpeacock Using Interrupts Page 2 What are Interrupts? When receiving data and change in status from I/O Ports, we have two methods available to us. We can Poll the port, which involves reading the status of the port at fixed intervals to determine whether any data has been received or a change of status has occurred. If so, then we can branch to a routine to service the ports requests. As you could imagine, polling the port would consume quite some time. Time which could be used doing other things such refreshing the screen, displaying the time etc. A better alternative would be to use Interrupts. Here, the processor does your tasks such as refreshing the screen, displaying the time etc, and when a I/O Port/Device needs attention as a byte has been received or status has changed, then it sends a Interrupt Request (IRQ) to the processor. Once the processor receives an Interrupt Request, it finishes its current instruction, places a few things on the stack, and executes the appropriate Interrupt Service Routine (ISR) which can remove the byte from the port and place it in a buffer. Once the ISR has finished, the processor returns to where it left off. Using this method, the processor doesnt have to waste time, looking to see if your I/O Device is in need of attention, but rather the device will interrupt the processor when it needs attention. Interrupts and Intel Architecture Interrupts do not have to be entirely associated with I/O devices. The 8086 family of microprocessors provides 256 interrupts, many of these are only for use as software interrupts, which we do not attempt to explain in this document. The 8086 series of microprocessors has an Interrupt Vector Table situated at 0000:0000 which extends for 1024 bytes. The Interrupt Vector table holds the address of the Interrupt Service Routines (ISR), all four bytes in length. This gives us room for the 256 Interrupt Vectors.
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