𝐖𝐡𝐚𝐭 𝐢𝐬 𝐚𝐧 𝐈𝐧𝐭𝐞𝐫𝐫𝐮𝐩𝐭?
At its core, an interrupt is a signal to the processor of an event that requires immediate attention. Imagine reading a book and suddenly your phone rings. You stop reading, answer the phone, and after finishing the call, you resume reading from where you left off. In this analogy, the phone call is an interrupt to your reading activity.
In computer terms, an interrupt alerts the CPU to pause its current task and address the new task related to the interrupt. Common sources of interrupts include Input/Output (I/O) activities, timers reaching their limit, or even error occurrences like trying to divide by zero.
𝐖𝐡𝐲 𝐚𝐫𝐞 𝐈𝐧𝐭𝐞𝐫𝐫𝐮𝐩𝐭𝐬 𝐈𝐦𝐩𝐨𝐫𝐭𝐚𝐧𝐭?
Efficiency: Instead of the CPU constantly checking the status of devices (known as “polling”), interrupts allow the CPU to work on other tasks until a device signals it needs attention.
Error Handling: Interrupts provide a mechanism for the system to handle unexpected events or errors in a controlled manner.
Routine Reminders: They can remind the CPU to perform routine tasks at regular intervals.
𝐈𝐧𝐭𝐞𝐫𝐫𝐮𝐩𝐭 𝐌𝐚𝐬𝐤𝐚𝐛𝐢𝐥𝐢𝐭𝐲:
Maskable Interrupts: These are the interrupts that the CPU can choose to ignore. Before they can interrupt the CPU, they must be enabled, typically by setting a flag.
Non-maskable Interrupts: These are critical interrupts that the CPU cannot ignore, often representing urgent system events.
𝐈𝐧𝐭𝐞𝐫𝐫𝐮𝐩𝐭 𝐏𝐫𝐢𝐨𝐫𝐢𝐭𝐲:
In scenarios where multiple interrupts occur simultaneously, a priority system determines which interrupt should be serviced first.
𝐒𝐞𝐫𝐯𝐢𝐜𝐢𝐧𝐠 𝐚𝐧 𝐈𝐧𝐭𝐞𝐫𝐫𝐮𝐩𝐭:
When an interrupt occurs, the CPU follows a sequence of steps:
1. Save the current state of the program, including the program counter and CPU status.
2. Determine the cause of the interrupt.
3. Locate the starting address of the appropriate Interrupt Service Routine (ISR) to handle the interrupt.
4. Execute the ISR.
5. Restore the saved state of the program and resume execution.
𝐈𝐧𝐭𝐞𝐫𝐫𝐮𝐩𝐭 𝐕𝐞𝐜𝐭𝐨𝐫 & 𝐕𝐞𝐜𝐭𝐨𝐫 𝐓𝐚𝐛𝐥𝐞:
The “Interrupt Vector” is the address of the ISR. All these vectors are stored in a table known as the “Interrupt Vector Table”. The method to determine these vectors varies across different microcontrollers and architectures.
𝐏𝐫𝐨𝐠𝐫𝐚𝐦𝐦𝐢𝐧𝐠 𝐰𝐢𝐭𝐡 𝐈𝐧𝐭𝐞𝐫𝐫𝐮𝐩𝐭𝐬:
1. Initialize the Interrupt Vector Table.
2. Write the Interrupt Service Routine to address the interrupt’s cause.
3. Enable the interrupt so that the CPU can recognize it.
𝐈𝐧𝐭𝐞𝐫𝐫𝐮𝐩𝐭 𝐎𝐯𝐞𝐫𝐡𝐞𝐚𝐝:
Handling an interrupt isn’t free; there’s an “overhead” or cost associated with it:
– Time taken to save and restore CPU status.
– Execution time of the ISR.
– Time for restoring the CPU state and resuming the main program.
Interrupts are crucial in embedded systems, allowing for efficient multitasking, timely responses to external events, and effective error handling. However, it’s essential to manage them effectively to ensure the system’s responsiveness and reliability.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
An Article by: Yashwanth Naidu Tikkisetty
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
