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Introduction to Polling
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Today we're going to discuss polling as a method of bus arbitration. Polling involves the CPU periodically checking the status of devices to see if they need access to the bus.
So, how does polling actually work?
Great question! The CPU systematically checks each device's status by reading a status register. If a device indicates it needs the bus, the CPU will grant access based on a predefined sequence.
What are its advantages over other methods?
One key advantage of polling is flexibility; the priority and order can be defined by software. However, this means the CPU spends time just checking statuses, which can be inefficient.
Can it be used for high-speed applications?
Not typically. Polling is not efficient for high-speed systems, but is common in simpler embedded systems where speed isn't as critical.
So, is polling always bad then?
Not necessarily. In applications where design simplicity is prioritized over execution speed, polling can be quite useful!
Let’s recap: Polling enables flexible bus access management at the cost of some efficiency compared to hardware-driven methods.
Advantages and Disadvantages of Polling
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Let's talk about the advantages and disadvantages of polling. Can anyone tell me a benefit of using polling?
It’s flexible, right? The system can change how devices are checked.
Exactly! Polling allows for a dynamic approach to arbitration. What about some disadvantages?
Does it use a lot of CPU cycles?
Yes! The CPU can waste valuable time checking devices instead of doing more complex tasks.
So, it's not good for high-speed applications?
Correct! Polling isn't the best choice for those situations. It’s suited for simpler systems where real-time performance is less of a concern.
To summarize, polling provides flexibility but can lead to inefficient use of CPU resources, making it less suitable for high-speed needs.
Polling in Embedded Systems
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Now, let’s explore how polling is applied in embedded systems. Can anyone think of scenarios where this might be useful?
Maybe in simple devices like sensors or timers?
Absolutely! In environments where devices have less demanding timing requirements, polling is often a viable solution.
Are there specific advantages in those cases?
For sure! The design simplicity is a huge advantage. It’s easier to implement polling rather than complex hardware arbitration methods.
Does that mean it’s also cheaper?
Yes! Reduced hardware requirements can lead to lower costs in simpler embedded systems.
In conclusion, while polling may not be optimal for all scenarios, it fits well in simple embedded systems where costs and design simplicity matter.
Introduction & Overview
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Quick Overview
Standard
In polling, the CPU does not respond to explicit bus requests from potential bus masters; instead, it systematically checks each device's status to determine if they require bus access. This method provides flexibility but can be inefficient, often consuming valuable CPU time that could be utilized for other tasks.
Detailed
Polling, a form of software-driven arbitration, contrasts with fixed hardware-based schemes by allowing the CPU or a dedicated polling agent to periodically check devices for bus access requests. This method enables flexibility in priority and polling order since these can be defined by software. However, the downside includes inefficiencies, as the CPU spends substantial cycles checking status rather than executing other tasks. Although rarely employed in high-speed bus systems due to inherent inefficiencies, polling can be beneficial in simpler embedded systems where real-time performance is less critical than design simplicity.
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Overview of Polling
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In this method, the CPU (or a dedicated polling agent) does not react to explicit bus requests from other masters. Instead, it systematically and periodically checks the status of various potential bus master devices (e.g., by reading a status register in each device) to determine if they require bus access. If a device indicates a need, the CPU then grants the bus to it based on a pre-programmed polling sequence or software-defined priority.
Detailed Explanation
Polling is a technique where the CPU does not wait for devices to request access to the bus. Instead, it actively checks each device in a predetermined order to see if they need to send or receive data. This approach allows for flexible interaction with devices, as the CPU controls who gets to use the bus and when, based on the status of each device at the time of checking.
Examples & Analogies
Imagine a teacher checking in on each student in a classroom, asking, 'Do you need help?' instead of waiting for a student to raise their hand. This method ensures that each student is given a chance to voice their need, allowing them to receive help as necessary, but it means the teacher must periodically check in rather than respond instantly.
Advantages of Polling
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Extremely flexible as the priority and polling order are entirely determined by software and can be easily changed at runtime. Requires minimal dedicated hardware for arbitration beyond standard I/O lines.
Detailed Explanation
One of the main benefits of polling is its flexibility. Since the system is controlled by software, the programmer can set the priorities and order in which devices are checked, making it easy to adapt to changing requirements or to optimize performance. Furthermore, polling typically needs less specialized hardware than other arbitration methods, simplifying design.
Examples & Analogies
Consider a car mechanic who can choose the order in which they check cars for repairs based on urgency or importance. If a new urgent repair comes in, they can adjust their order and prioritize that car without needing to change any tools or elaborate systems. This adaptability helps manage work effectively.
Disadvantages of Polling
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Inherently inefficient and slow. The CPU spends a significant portion of its time actively checking device statuses, consuming valuable CPU cycles that could be used for other tasks. This makes it unsuitable for high-speed bus masters or systems with stringent real-time requirements where rapid bus grants are essential.
Detailed Explanation
Despite its benefits, polling can be inefficient. Since the CPU is constantly checking each device rather than performing other operations, it can waste cycles, especially when devices do not need to communicate frequently. This process can lead to delays in systems where immediate access to the bus is critical, as the CPU might miss opportunities to perform other tasks or respond to urgent requests.
Examples & Analogies
Think of a receptionist at a busy hotel who periodically walks through the lobby asking guests if they need help, rather than staying at the desk to help those who actively approach. While the receptionist checks in with many guests, they might miss out on important requests or new arrivals needing immediate assistance, leading to inefficient service during peak times.
Common Usage of Polling
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Rarely used for general high-speed bus arbitration due to its inefficiency. However, the concept of polling is very common in simpler embedded systems for managing routine I/O operations where real-time performance is less critical than design simplicity.
Detailed Explanation
Polling is less favored in high-speed computing because it does not provide the immediate access required for many applications. However, in simpler embedded systems—like those managing low-frequency I/O operations—polling can be an effective strategy, as the demands for immediate response are lower, and the ease of implementation can save on costs and complexity.
Examples & Analogies
Imagine a simple digital clock that only updates the time every minute. It checks its timekeeping system once every minute rather than continuously updating or seeking readings. Thus, it has a simpler design that is sufficient for its purpose, even if it's not the most efficient way of keeping track of time.
Definitions & Key Concepts
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Key Concepts
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Polling: A technique for bus arbitration where the CPU periodically checks devices for access.
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Efficiency: Polling can lead to inefficient CPU usage due to the time spent checking device statuses.
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Embedded systems: Polling is suitable for applications where speed is not critical.
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Flexibility: The order of polling and device priority can be defined by software.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
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In a simple embedded system, an Arduino might poll the temperature sensors every second to update the display.
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Polling can be used in a keyboard controller where the CPU checks the status of key presses at regular intervals.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
🎵 Rhymes Time
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Polling every hour, gives devices the power, to speak to the CPU, for tasks they must do.
📖 Fascinating Stories
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Imagine a careful librarian (the CPU) who checks in with every book (devices) periodically to see if it's in the right place or needs attention.
🧠 Other Memory Gems
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Remember 'P-Check' for Polling: P for Periodic, C for Checks on devices.
🎯 Super Acronyms
P.A.C.E.
- Polling Allows Check Efficiency — a reminder that polling helps manage multiple device requests.
Flash Cards
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Glossary of Terms
Review the Definitions for terms.
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Term: Polling
Definition:
A method of bus arbitration where the CPU periodically checks the status of devices to determine bus access.
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Term: Bus Arbitration
Definition:
The mechanism used to control access to the shared data bus in a computer system.
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Term: Bus Master
Definition:
A device capable of initiating data transfers on a bus.
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Term: Status Register
Definition:
A register in a device that indicates its status and whether it requires bus access.