Interrupt Initiated IO

Duration: 7 min

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  23. UPPSC Live Class Recordings: UPPSC Polytechnic Lecturer 2025 (CS)
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AI summary & chapters

AI Summary

An AI-generated summary of this video lecture.

The video lecture provides a detailed explanation of Interrupt Initiated I/O, a method where I/O devices signal the CPU to initiate data transfer. The instructor begins by defining the process: the CPU executes instructions and checks for interrupts between them. If an interrupt occurs, the CPU decides whether to handle it. A crucial note is that instructions are absolute, meaning partial execution is not possible. The lecture then introduces Interrupt Service Routines (ISRs) as the programs that manage these interrupts. The session transitions to classifying interrupts into two types: Non-vectored, where the location is mutually understood, and Vectored, where the device provides the address. Finally, the lecture addresses priority handling using a hardware solution called Daisy Chaining, illustrated with a diagram of three devices connected in a serial chain to the CPU.

Chapters

  1. 0:00 – 2:00 00:00-02:00

    The slide titled 'Interrupt initiated i/o' is displayed. The instructor explains that in this method, the I/O device interrupts the CPU when ready for data transfer. The CPU continues executing instructions and checks for interrupts after each instruction. A key note on the slide states that instructions are absolute in nature, implying no partial execution. The instructor also mentions that every device has a specific program or routine called an ISR (Interrupt Service Routine) to manage the interrupt, which saves CPU time. The text on the slide explicitly mentions 'CPU keep executing instructions and after executing one instruction and before starting another instructions CPU wait and see if there is interrupt or not'.

  2. 2:00 – 5:00 02:00-05:00

    The slide changes to 'Interrupt can be of two types'. The instructor defines Non-vectored interrupt as having a mutual understanding between CPU and device regarding the routine's location. In contrast, a Vectored interrupt involves the device telling the CPU the address where the routine is stored. The slide also notes that if different I/O devices interrupt simultaneously, the CPU must decide priority. The lecture then introduces a hardware solution known as Daisy Chaining, showing a diagram with Device 1, Device 2, and Device 3 connected in a serial line to the CPU. The text 'H/w solution: - It can be serial or parallel, serial solution is known as Daisy Channing' is visible.

  3. 5:00 – 6:48 05:00-06:48

    The instructor elaborates on the Daisy Chaining diagram, drawing red arrows to trace the signal flow. He explains that the device placed first in the arrangement gets acknowledgment first. If it wants to perform I/O, it puts 0 on the priority outline and places the ISR address on the vector address line. If it does not want to perform I/O, it sets the priority output to 1, passing the chance to the second device. The slide lists advantages such as being simple, easy to use, and relatively fast. The disadvantage noted is that the priority is fixed and cannot be changed even if requirements change. The instructor draws a red arrow from the CPU's INT ACK line back to the first device.

The lecture systematically builds an understanding of interrupt management. It starts with the basic interaction between CPU and I/O devices, emphasizing the non-blocking nature of interrupt-driven I/O compared to polling. It then distinguishes between interrupt types based on address resolution, highlighting the efficiency of vectored interrupts. The final section focuses on the practical hardware implementation of priority resolution through Daisy Chaining. By analyzing the diagram and the instructor's explanation of signal propagation (Interrupt Request and Interrupt Acknowledge), students learn how hardware logic determines which device gets serviced first. The trade-off between simplicity and flexibility (fixed priority) is clearly outlined, providing a complete picture of this specific I/O control method.

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