What is an interrupt ?
An interrupt is a piece of code that starts executing automatically when an event occurs. To do this it has to interrupt whatever code was running before the event occurred. As part of this, the Program Counter (PC) is saved on the GB stack and interrupts are turned off as soon as the interrupt code starts executing. At the end of the interrupt, a RETI assembly instruction is usually executed which returns to executing code that was running before the interrupt occurred and enables interrupts again.
Since the processor cannot process multiple pieces of data at the same time (it processes one piece of data a time, multitasking is actually the alternation of instruction snippets from several different tasks), a currently running program can be momentarily suspended by an interrupt for the time it takes to execute an interrupt service routine. The interrupted program may then continue executing. There are 256 different interrupt addresses. An interrupt is a hardware interrupt when it is requested by a hardware component of the computer. A computer has many peripherals. They generally need to use system resources, if only to communicate with the system… When they need a resource, they send an interrupt request to the system so that the system will pay attention to them. The peripherals each have an interrupt number, called an IRQ (Interruption request). One way of imagining this is to view each peripheral as pulling on a “string” connected to a bell to signal to the computer that it
