External and Internal Interrupts

Pre-requisites: Interrupts, Software, and Hardware interrupts

The interrupt is a signal emitted by hardware or software when a process or an event needs immediate attention. It alerts the processor to a high-priority process requiring interruption of the current working process.

There are two major types of interrupts that cause a break in the normal execution of a program. Those types are:

1. External interrupts 
2. Internal interrupts

External Interrupts : 

External interrupts come from input-output I/O devices. 

Some examples that cause external interrupts: 

•  I/O devices requesting transfer of data 
•  I/O devices finished the transfer of data. When a program executes in an endless loop and thus exceeds its time limit, an external interrupt occurs which is Timeout Interrupt.
• While transferring the CPU’s complete state to a non-destructive memory in a few milliseconds before power ceases, then an external interrupt occurs.

Advantages of External Interrupts

• Increased Flexibility: External interrupts allow a system to respond to external events, such as a user input or an external sensor, in real-time. This can greatly improve the system’s flexibility, as it is not limited to a fixed operating cycle.
• Ability to Respond to External Events: External interrupts provide a mechanism for the system to respond to external events that may occur at any time. This allows the system to perform tasks in response to changes in the environment, such as user input or incoming data, without the need for continuous monitoring.
• Improved Performance and Efficiency: By allowing the system to respond to external events in real-time, external interrupts can greatly improve the system’s performance and efficiency, as it is not bogged down by continuous monitoring for changes.

Applications of External Interrupts

• Input Devices: External interrupts are commonly used in input devices, such as keyboards, mice, and touchpads, to respond to user input in real-time.
• Data Acquisition Systems: External interrupts can be used in data acquisition systems to respond to incoming data and process it in real-time.
• Robotics: External interrupts can be used in robotics systems to respond to external events, such as sensor inputs or user commands.
• Real-time Systems: External interrupts are commonly used in real-time systems, such as process control systems and medical equipment, to provide a mechanism for responding to external events in real-time.

Internal Interrupts :

Internal interrupts also known as traps, arise from the illegal use of an instruction. 

Some examples that cause external interrupts: 

• Register Overflow.
• Attempt to divide by zero
• Invalid operation code.
• Stack overflow.
• Protection violation.

These conditions usually occur because of premature termination of the instruction execution.

Advantages of Internal Interrupts

• Ease of Use: Internal interrupts are typically easier to implement than external interrupts, as they are triggered by internal events, such as timer overflows, rather than external events.
• Improved Performance: By using internal interrupts, the system can operate at a higher performance level, as it is not limited by the need to respond to external events.
• Consistent Response Times: Internal interrupts provide consistent response times, as they are triggered by internal events, which are predictable and consistent.

Applications of Internal Interrupts

• Timer-based Systems: Internal interrupts are commonly used in timer-based systems to trigger periodic events, such as timekeeping, scheduling, and task switching.
• Real-time Systems: Internal interrupts can be used in real-time systems to provide a consistent, real-time response to internal events.
• Embedded Systems: Internal interrupts are commonly used in embedded systems, such as microcontrollers, to handle internal events, such as timer overflows, without the need for external events.
• Multitasking Systems: Internal interrupts are used in multitasking systems to switch between tasks, manage task scheduling, and provide real-time response to internal events.

Difference between External Interrupts vs Internal Interrupts

External Interrupts	Internal Interrupts
External interrupts are caused by some external event or failure.	Internal interrupts are caused by some exceptional condition caused by program itself rather than by an external event.
External interrupts are asynchronous.	Internal interrupts are synchronous with the program.
External interrupts depend on external conditions that are independent of the program being executed at that time.	If the program is returned, Internal interrupts will occur in the same place each time.