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Lecture Introduction to computing systems (2/e): Chapter 8 - Yale N. Patt, Sanjay J. Patel

The main contents of this chapter include all of the following: I/O basics; input from the keyboard; output to the monitor; a more sophisticated input routine; interrupt-driven I/O; implementation of memory-mapped I/O, revisited. | Chapter 8 I/O I/O: Connecting to Outside World So far, we’ve learned how to: compute with values in registers load data from memory to registers store data from registers to memory But where does data in memory come from? And how does data get out of the system so that humans can use it? 8- I/O: Connecting to the Outside World Types of I/O devices characterized by: behavior: input, output, storage input: keyboard, motion detector, network interface output: monitor, printer, network interface storage: disk, CD-ROM data rate: how fast can data be transferred? keyboard: 100 bytes/sec disk: 30 MB/s network: 1 Mb/s - 1 Gb/s 8- I/O Controller Control/Status Registers CPU tells device what to do -- write to control register CPU checks whether task is done -- read status register Data Registers CPU transfers data to/from device Device electronics performs actual operation pixels to screen, bits to/from disk, characters from keyboard Graphics Controller Control/Status Output Data Electronics CPU display 8- Programming Interface How are device registers identified? Memory-mapped vs. special instructions How is timing of transfer managed? Asynchronous vs. synchronous Who controls transfer? CPU (polling) vs. device (interrupts) 8- Memory-Mapped vs. I/O Instructions Instructions designate opcode(s) for I/O register and operation encoded in instruction Memory-mapped assign a memory address to each device register use data movement instructions (LD/ST) for control and data transfer 8- Transfer Timing I/O events generally happen much slower than CPU cycles. Synchronous data supplied at a fixed, predictable rate CPU reads/writes every X cycles Asynchronous data rate less predictable CPU must synchronize with device, so that it doesn’t miss data or write too quickly 8- Transfer Control Who determines when the next data transfer occurs? Polling CPU keeps checking status register until new data arrives OR device ready for next data “Are we there yet? Are we | Chapter 8 I/O I/O: Connecting to Outside World So far, we’ve learned how to: compute with values in registers load data from memory to registers store data from registers to memory But where does data in memory come from? And how does data get out of the system so that humans can use it? 8- I/O: Connecting to the Outside World Types of I/O devices characterized by: behavior: input, output, storage input: keyboard, motion detector, network interface output: monitor, printer, network interface storage: disk, CD-ROM data rate: how fast can data be transferred? keyboard: 100 bytes/sec disk: 30 MB/s network: 1 Mb/s - 1 Gb/s 8- I/O Controller Control/Status Registers CPU tells device what to do -- write to control register CPU checks whether task is done -- read status register Data Registers CPU transfers data to/from device Device electronics performs actual operation pixels to screen, bits to/from disk, characters from keyboard Graphics Controller Control/Status Output Data .