How do you use interrupt masking and unmasking to control interrupt requests in microprocessor?

1 What is interrupt masking and unmasking?

Interrupt masking and unmasking are techniques to enable or disable the recognition of interrupt requests by the microprocessor. When an interrupt is masked, it means that the microprocessor will ignore it, even if the interrupt signal is active. When an interrupt is unmasked, it means that the microprocessor will acknowledge it, if the interrupt signal is active and has a higher priority than the current task. Interrupt masking and unmasking can be done by hardware or software methods.

2 How to use hardware interrupt masking and unmasking?

Hardware interrupt masking and unmasking are done by using special pins or registers on the microprocessor or the interrupt controller. For example, some microprocessors have a pin called INTR (interrupt request) that can be connected to an external device that generates interrupts. When the INTR pin is high, it means that an interrupt request is pending. The microprocessor can mask or unmask this pin by using another pin called INTA (interrupt acknowledge) that signals the acceptance or rejection of the interrupt request. Some microprocessors also have a pin called NMI (non-maskable interrupt) that cannot be masked by the INTA pin and always triggers an interrupt.

3 How to use software interrupt masking and unmasking?

Software interrupt masking and unmasking are done by using special instructions or flags on the microprocessor or the operating system. For example, some microprocessors have an instruction called CLI (clear interrupt flag) that clears a bit in the status register called IF (interrupt flag). When the IF bit is cleared, it means that the microprocessor will not respond to any interrupt requests, except for NMI. To unmask the interrupts, the microprocessor can use another instruction called STI (set interrupt flag) that sets the IF bit. Some operating systems also have system calls or functions that can mask or unmask specific interrupt requests.

4 Why to use interrupt masking and unmasking?

Interrupt masking and unmasking are useful for controlling the timing and order of interrupt requests in microprocessor. By masking and unmasking interrupts, the microprocessor can avoid unwanted interruptions, prioritize critical tasks, prevent conflicts or errors, and optimize performance and power consumption. For example, the microprocessor can mask interrupts when it is executing a time-sensitive or atomic operation that cannot be interrupted, such as updating a shared variable or accessing a critical resource. The microprocessor can unmask interrupts when it is idle or waiting for an event, such as a user input or a sensor reading.

5 How to handle multiple interrupt requests?

When the microprocessor receives multiple interrupt requests, it has to decide which one to service first. This depends on the priority scheme that the microprocessor or the interrupt controller follows. There are different ways to assign priority to interrupt requests, such as fixed priority, programmable priority, rotating priority, or nested priority. The priority scheme determines which interrupt request will be serviced first, which one will be postponed, and which one will be lost. The microprocessor also has to save the current state of the program before servicing an interrupt request, and restore it after returning from the interrupt service routine.

6 What are the challenges of interrupt masking and unmasking?

Interrupt masking and unmasking can be challenging due to the need to find a balance between masking and unmasking interrupts, as well as dealing with nested or concurrent interrupts. Additionally, spurious or false interrupts can occur due to noise or glitches in the interrupt signals or circuits, and managing the latency or overhead of interrupt processing can affect the performance or accuracy of the program.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?