Deep Dive: x86 and ARM
When a computer is executing a program, it needs to be able to respond to external events such as keyboard input, network traffic, or hardware errors. Interrupts and exceptions are mechanisms that allow the computer to temporarily suspend the current program and handle the event before returning to the program. In this lesson, we will focus on interrupts and exceptions in the x86 architecture.
An interrupt is a signal that is sent to the processor from an external source. The signal indicates that an event has occurred that requires the processor's attention. Interrupts can be generated by hardware devices such as a keyboard, mouse, or network card, or they can be generated by software such as a system call or an error condition.
When an interrupt occurs, the processor saves the current state of the program, including the value of the program counter, registers, and flags, onto the stack. It then jumps to a predefined memory location called an interrupt vector table, which contains the addresses of interrupt service routines (ISRs) that handle specific types of interrupts. The ISR performs the required operations to service the interrupt and then returns the control back to the interrupted program by restoring the saved state from the stack.
Exceptions are similar to interrupts but are generated by the processor itself in response to internal error conditions or exceptional events such as division by zero or page faults. Exceptions also use the same mechanism as interrupts to suspend the current program and transfer control to an exception handler, which is a special routine that handles the specific type of exception. Once the exception has been handled, the control is returned to the interrupted program.
In x86 architecture, there are two types of interrupts: hardware interrupts and software interrupts. Hardware interrupts are generated by external devices and are assigned a unique interrupt number. Software interrupts are generated by software and use a special instruction called INT to generate the interrupt. The INT instruction takes a single byte operand that specifies the interrupt number to be generated. Similarly, exceptions are also assigned unique exception numbers and are handled by exception handlers that are registered with the operating system.
In summary, interrupts and exceptions are crucial mechanisms that allow a computer to handle external events and exceptional conditions. They enable the computer to respond to external inputs and internal errors in a controlled and predictable manner, which is essential for the reliable operation of a computer system.
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