Brief

In the x86 architecture --8259A interrupt controller , we have to introduce, through 8259A interrupt controller, the system can connect up to 64 interrupt sources, but in actual use, if you really use the 8259A 8 pieces, the system design It will be very difficult. Therefore, in actual use, we can use a general or a 8259A chip 2, thus constituting a maximum of 16 interrupt (one or cascaded with, the actual on 15).

However, with the development of computer systems, need access to more and more equipment, especially the introduction of PCI devices, resulting in the number of interruptions it is not enough, in order to solve this problem, we introduced the concept of interrupt sharing, in order to better support PCI devices, and the introduction of PCI interrupt (ie article title referred PCI IRQ).

This paper describes the PCI IRQ. Note that, this thing PCI devices need extra pins to support, follow-up with the introduction of MSI interrupts, PCI IRQ has basically been eliminated, so this is also part of the archaeological culture.

Description PCI specification IRQ

Below is specified the device PIN pin PCI specification:

Note that the red box part of PIN feet, they are for the interruption, they have the following characteristics:

1. Alternatively, as in the case of MSI, the interrupt walk PCI protocol, no additional pins to support;

2. A total of four pins, dB is ABCD;

3. For multi-function (Multi-Functions) devices will be used to pin outside the INTA #, otherwise you can only use INTA #;

These are hardware configuration, when the pin is determined, the need to configure the software, which requires use of the contents inside the PCI configuration space, as follows:

This is the PCI configuration space, the red part is configured on the PCI IRQ.

Interrupt Pin: Specifies the INTA # / INTB # / INTC # / INTD # one, 1 INTA #, 2 denotes INTB #, and so on;

Interrupt Line: Specifies the PCI IRQ interrupt controller is connected to which of the interrupt (interrupt number, such as 8259A, it is interesting that the general 8259A interrupt A / B is the flow out to a PCI IRQ, a correspondence relationship just formed, However, this correspondence is not required).