Advanced Operating Systems: Lecture 35 - Mr. Farhan Zaidi

Advanced Operating Systems - Lecture 35: Principles of I/O software. This lecture will cover the following: goals of I/O software; layers of I/O software; direct vs memory mapped I/O; interrupt driven I/O; polled I/O; direct memory access (DMA);...

CS703 ­ Advanced  Operating Systems By Mr Farhan Zaidi Lecture No.  35 Overview of today’s lecture       Goals of I/O software Layers of I/O software Direct Vs memory mapped I/O Interrupt driven I/O Polled I/O Direct Memory Access (DMA) Principles of I/O Software   Goals of I/O Software Device independence  Uniform naming    handle as close to the hardware as possible Synchronous vs asynchronous transfers   name of a file or device a string or an integer not depending on which machine Error handling   programs can access any I/O device without specifying device in advance (floppy, hard drive, or CD-ROM) blocked transfers vs interrupt-driven Buffering  data coming off a device cannot be stored in final destination immediately Device Controllers  I/O devices have components:    The electronic component is the device controller   mechanical component electronic component may be able to handle multiple devices Controller's tasks    convert serial bit stream to block of bytes perform error correction as necessary make available to main memory Layers of the I/O system and the main  functions of each layer Memory mapped I/O Vs Direct I/O  Memory mapped I/O   Device controller’s registers and internal memory are directly mapped into the processor’s address space Direct I/O  Device controller’s registers and internal memory is accessible via special instructions in the assembly language instruction set The arguments to these instructions are usually called ports Programmed I/O  Writing a string to the printer using programmed I/O Interrupt­Driven I/O  Writing a string to the printer using interrupt-driven I/O a Code executed when print system call is made b Interrupt service procedure A Typical Hardware System CPU chip register file ALU system bus memory bus main memory I/O bridge bus interface I/O bus USB controller mouse keyboard graphics adapter disk controller monitor disk Expansion slots for other devices such as network adapters Reading a Disk Sector: Step 1 CPU chip register file ALU CPU initiates a disk read by writing a  command, logical block number, and destination memory address to a port (address) associated with disk controller main memory bus interface I/O bus USB controller mouse keyboard graphics adapter disk controller monitor disk Reading a Disk Sector: Step 2 CPU chip register file ALU Disk controller reads the sector and performs a direct memory access (DMA) transfer into main memory main memory bus interface I/O bus USB controller mouse keyboard graphics adapter disk controller monitor disk Reading a Disk Sector: Step 3 CPU chip register file ALU When the DMA transfer completes, the disk controller notifies the CPU with an interrupt (i.e., asserts a special “interrupt” pin on the CPU) main memory bus interface I/O bus USB controller mouse keyboard graphics adapter disk controller monitor disk Direct Memory Access (DMA) Operation of a DMA transfer I/O Using DMA  Printing a string using DMA a code executed when the print system call is made b interrupt service procedure .. .Lecture? ?No.  35 Overview of today’s? ?lecture       Goals of I/O software Layers of I/O software Direct Vs memory... any I/O device without specifying device in advance (floppy, hard drive, or CD-ROM) blocked transfers vs interrupt-driven Buffering  data coming off a device cannot be stored in final destination... printer using programmed I/O Interrupt­Driven I/O  Writing a string to the printer using interrupt-driven I/O a Code executed when print system call is made b Interrupt service procedure A Typical Hardware System