how single irq line is shared at physical hardware among multiple devices

Question

I want to know how one single irq line is shared among multiple devices, i mean how they are physically connected at hardware level, do they use multiple APIC controllers for this, or what other methods are used.

Answer 1

The most basic way to connect multiple devices to a single interrupt request line, so that every device can activate a request, is to use open collector.
When the request is granted, the acknowledge signal may be forwarded from device to device using a daisy chain.