Question

interrupts..microprocessors

Introduction to Microprocessors We Woods IN MOV d e Roubos 8 Interrupts A. From the wikipedia article, name at least nine typical uses of interrupts. B. How can a microprocessor keep time, using interrupts ? C. In systems that are equipped with a power-off interrupt, what is the purpose of the power-off interrupt (many UNIX and Linux systems have a power off interrupt) ? D. The steps of interrupt processing in a micro-processor are broadly analogous to the steps of receiving a phone call on an old-style phone. For each of these microprocessor steps, indicate the analogous step in receiving a phone call Analogous step in receiving a phone call (1) Interrupt request arrives (2) Return address is stored (3) Interrupt service routine is activated (4) Interrupt service routine completes (5) Action of the RETFIE instruction

Answer 1

A. Nine typical uses from the wikipedia article are: -

1) Interrupts are commonly used by hardware devices to indicate electronic or physical state changes that require attention.

2) Interrupts are also commonly used to implement computer multitasking, especially in real-time computing.

3) Interrupts are commonly used to service hardware timers.

4) transfer data to and from storage (e.g., disk I/O)

5) communication interfaces (e.g., UART, Ethernet),

6) handle keyboard and mouse events

7) to respond to any other time-sensitive events as required by the application system.

8) Non-maskable interrupts are typically used to respond to high-priority requests such as watchdog timer timeouts, power-down signals and traps.

9) Periodic interrupts are also commonly used to invoke sampling from input devices such as analog-to-digital converters, incremental encoder interfaces, and GPIO inputs, and to program output devices such as digital-to-analog converters, motor controllers, and GPIO outputs.

10) Interrupts are counted by interrupt handler to keep track of time elapsed, or used by the OS task scheduler to manage execution of running processes.

B.

There are two types of interrupts Hardware interrupt and software interrupt. So first lets discuss hardware interrupt, where it is used to keep track of time.

The hardware which is integrated to the microprocessor is supplied with a clock. Or you can say the microprocessor is the master and the hardware is the slave. I hope you are familiar with master-slave concept. Even if you are not, in simple terms microprocessor has interrupt handler which counts the number of interrupt which is basically the elapsed time. frequency of the hardware should be proper so that between each interrupt the delay is 1 sec. That means 2 interrupt is 2 sec 5 interrupt is 5 sec. It can be calibarated by proper clock frequency given to the hardware device

Now, we come to software interrupt, for this kind of interrupts no external device is required hence it is cheap but the problem here is your microprocessor gets busy generating interrupts and counting them, which was totally different in case of hardware interrupts the microprocessor was free to do anything. The concept is same.. Interrupts are generated and counted by interrupt handler to keep track of elapsed time.

C.

The pupose of power -off interrupt is a power-off interrupt predicts imminent loss of power, allowing the computer to perform an orderly shut-down while there still remains enough power to do so.

D.

Lets assume that your phone is in your pocket in a normal state and at that moment lets assume microprocessor in some random address say 0x01H. Now suddenly your phone rings.

1) Interrupt request arrives: Phone rings analogous to an interrupt signal recevied by a microprocessor.

2) Return address is stored: So as the microprocessor was at 0x01H it will push that address to a stack and go to the Interrupt Service Routine(ISR) of the interrupt arriving at that moment analogous to you doing some work leaving it in the middle and picking up the phone. (Remeber what you were doing => return address storing).

3) Interrupt service routine is activated: Now you pick up the call that is you are performing the ISR, which exactly the microprocess also does.(You pick up the call => microprocessor performing the ISR).

4) Interrupt routine service completes: Your converstation is finished and you ended the phone call analogous to microprocessor finishing the ISR.

5) Action of RETFIE instruction: You return to what you were doing analogous to microprocessor returning to the address it was at earlier 0x01H.