Vectored interrupt

In computer science, a vectored interrupt is a processing technique in which the interrupting device directs the processor to the appropriate interrupt service routine. This is in contrast to a polled interrupt system, in which a single interrupt service routine must determine the source of the interrupt by checking all potential interrupt sources, a slow and relatively laborious process. A vectored interrupt is a type of interrupt handling mechanism in computer systems. In computing, an interrupt is a signal to the processor that an event has occurred, requiring its attention. Interrupts are used to handle various events, such as hardware events, errors, or requests for services, in a more efficient and timely manner than continuously polling for these events.

In the context of vectored interrupts, when an interrupt occurs, the interrupting device or component provides the processor with additional information called a vector. This vector is essentially a numeric identifier or address that points to the specific interrupt service routine (ISR) associated with the interrupting device.

Here's a breakdown of how vectored interrupts typically work:

Interrupt Occurs: Some event or condition triggers an interrupt.

Vector Provided: The interrupting device sends a vector to the processor. This vector is a unique identifier that helps the processor determine the specific service routine to execute.

Interrupt Service Routine (ISR): The processor uses the vector to locate the appropriate ISR in a predefined table or memory location. The ISR is a piece of code that handles the specific interrupt.

Processing: The processor jumps to the address specified by the vector and starts executing the ISR. The ISR performs the necessary actions to handle the interrupt, which may include saving the current state of the processor, performing specific tasks related to the interrupt, and restoring the processor's state afterward.

Return to Normal Execution: After the ISR completes its tasks, the processor returns to the interrupted program or task.

Vectored interrupts are often more efficient than non-vectored interrupts because they directly indicate the location of the corresponding ISR. This eliminates the need for the processor to search for the appropriate handler, resulting in faster and more predictable interrupt handling. This mechanism is commonly used in various computer architectures and embedded systems to efficiently manage and respond to interrupts.

Implementation

Vectored interrupts are achieved by assigning each interrupting device a unique code, typically four to eight bits in length. When a device interrupts, it sends its unique code over the data bus to the processor, telling the processor which interrupt service routine to execute.