Polling vs Interrupts: A Detailed Comparison of Methods

This report provides a detailed comparison between polling and interrupt methods used in computer systems for device servicing. It begins by defining interrupts as hardware mechanisms that allow the CPU to respond to device requests, contrasting them with polling, where the CPU regularly checks the status of devices. The report outlines the types of interrupts, including hardware and software interrupts, and explains the polling protocol. A comparison chart highlights the key differences between the two approaches, focusing on their basic mechanisms, servicing methods, and CPU interaction. Furthermore, the report discusses various methods of device polling based on priority and concludes by referencing relevant literature on embedded hardware and microprocessors. Desklib offers a wealth of similar solved assignments and study resources for students.

POLLING AND INTERRUPTS
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 Interrupts
 An interrupt refers to a hardware mechanism which allows CPU to sense a device
which requires its attention.
 Immediately the CPU senses that there is an interrupting wave on the interrupt-request
line, CPU halts instantly the activity it was executing and immediately responds to
interrupt sent by device [1].
 The handler of interrupts immediately resolves the interrupt through servicing the
device.

Types of interrupts  An interrupt refers to a signal to the processor showing a
device that needs instant attention
 There are two types of interrupt;
 Hardware for example pressing on the key found on the
keyboard which makes the keyboard send interrupts to the
microcontroller which in turn reads the information of the
pressed key
Software
A hardware interrupt refers to an electronic notifying indication sent to the CPU from an external device.
A software interrupt is produced either by a special condition or an unusual command in the instruction set that sources an
interrupt when it is executed by the processor.

 polling
 Each time the device is given a command, for example ``move the read head to sector 42 of the
floppy disk'' the device driver has a choice as to how it finds out that the command has
completed. The device drivers polls the device
 Polling refers to the protocol which allows the CPU which devices requires its attention.
 With polling the CPU is not affected unexpectedly since the CPU continuous to make regular
checks for the status of the device.
 CPU polls the devices at consistent breaks

 Comparison chart
BASIS INNTERRUPT POLLING
Basic The devices tells CPU its status The CPU checks devices status
Mechanism Hardware mechanism Protocol
Servicing Devices serviced by handler Device serviced by CPU
Indication The interrupt-requesting indicates Command-ready bit indicates
CPU CPU only disturbed when there is
need for serving the device
CPU waits and check if a device
needs serving
Occurrence An happens at any time CPU polls the device at given
times

 Difference between the Polling and interrupt
 In interrupt, device alerts the CPU that it requires servicing while, polling CPU frequently looks
if a given device wants attention.
 Interrupt refers to a hardware mechanism while the pooling is a protocol mechanism.
 . Interrupt handler resolves the interrupts while polling, the CPU specifically services a device
in the situations where there is need.
 Usually the Interrupts are detected by the interrupt-request line. While in polling bit shows the
device that requires attention[2] .

 Methods of device Polling according to priority
 Device polling can be according to priority, usually beginning from highest priority
 Device polling can be according to no-specific, priority, usually beginning from second
priority to the least serviced device.
 Device polling can be according to no-specific priority, usually starting from next priority to
the least serviced device
 For fexample when a CPU regulary checks for the updates.The updates are installed depending
on their priority in the CPU.

 References
[1] J. Catsoulis, Designing Embedded Hardware, London: "O'Reilly Media, Inc.",
2013.
[2] A. P. Mathur, Introduction to Microprocessors, Chicago: ata McGraw-Hill
Education, 2013.