CSN221_Lec_35 Computer Architecture and Microprocessor
- 1. Course Website: http://faculty.iitr.ac.in/~sudiproy.fcs/csn221_2015.html Piazza Site: https://piazza.com/iitr.ac.in/fall2015/csn221 Dr. Sudip Roy CSN‐221: COMPUTER ARCHITECTURE AND MICROPROCESSORS Input/Output (I/O) Devices (Lecture – 35)
- 2. Dr. Sudip Roy 2 Introduction to I/O:
- 3. Dr. Sudip Roy 3 I/O Peripherals:
- 4. Dr. Sudip Roy 4 External Device Block Diagram: External Devices: Human readable Screen, printer, keyboard Machine readable Monitoring and control Communication Modem Network Interface Card (NIC)
- 5. Dr. Sudip Roy 5 I/O Problems: Wide variety of peripherals Delivering different amounts of data At different speeds In different formats All slower than CPU and RAM Need I/O modules I/O Module: Interface to CPU and Memory Interface to one or more peripherals
- 6. Dr. Sudip Roy 6 I/O Module Diagram: Generic Model of I/O Module
- 7. Dr. Sudip Roy 7 I/O Module Function: Control & Timing CPU Communication Device Communication Data Buffering Error Detection CPU checks I/O module device status I/O module returns status If ready, CPU requests data transfer I/O module gets data from device I/O module transfers data to CPU Variations for output, DMA, etc. I/O Steps:
- 8. Dr. Sudip Roy 8 I/O Module Decisions: Hide or reveal device properties to CPU Support multiple or single device Control device functions or leave for CPU Also O/S decisions e.g. Unix treats everything it can as a file Input Output Techniques: Programmed I/O Interrupt driven I/O Direct Memory Access (DMA)
- 9. Dr. Sudip Roy 9 Three Techniques for Input of a Block of Data:
- 10. Dr. Sudip Roy 10 Programmed I/O: CPU has direct control over I/O Sensing status Read/write commands Transferring data CPU waits for I/O module to complete operation Wastes CPU time CPU requests I/O operation I/O module performs operation I/O module sets status bits CPU checks status bits periodically I/O module does not inform CPU directly I/O module does not interrupt CPU CPU may wait or come back later Programmed I/O ‐ Details: Addressing I/O Devices: Under programmed I/O data transfer is very much like memory access (CPU viewpoint) Each device given unique identifier CPU commands contain identifier (address)
- 11. Dr. Sudip Roy 11 I/O Mapping: Isolated I/O Separate address spaces Need I/O or memory select lines Special commands for I/O Limited set Memory mapped I/O Devices and memory share an address space I/O looks just like memory read/write No special commands for I/O Large selection of memory access commands available
- 12. Dr. Sudip Roy 12 Type of Peripheral I/O: Isolated I/O
- 13. Dr. Sudip Roy 13 Changes in Memory and Registers for an Interrupt:
- 14. Dr. Sudip Roy 14 Interrupt Driven I/O: Overcomes CPU waiting No repeated CPU checking of device I/O module interrupts when ready Basic Operations: CPU issues read command I/O module gets data from peripheral whilst CPU does other work I/O module interrupts CPU CPU requests data I/O module transfers data
- 15. Dr. Sudip Roy 15 Simple Interrupt Processing:
- 16. Dr. Sudip Roy 16 Interrupt Processing: CPU Viewpoint Issue read command Do other work Check for interrupt at end of each instruction cycle If interrupted:‐ Save context (registers) Process interrupt Fetch data & store Will have more discussion in Operating Systems classes
- 17. Dr. Sudip Roy 17 Interrupt‐driven I/O Design Issues: Identifying Interrupting Module: Software poll CPU asks each module in turn to determine which module caused the interrupt Slow Daisy Chain or Hardware poll All I/O modules share a common interrupt request line Interrupt acknowledge line is daisy chained through the modules When the processor senses an interrupt it sends out an interrupt acknowledge Module responsible places vector on bus CPU uses vector to identify handler routine
- 18. Dr. Sudip Roy 18 Steps to Implement Interrupt:
- 19. Dr. Sudip Roy 19 Interrupts & Priority:
- 20. Dr. Sudip Roy 20 Interrupts & Priority: Multiple Interrupts: Each interrupt line has a priority Higher priority lines can interrupt lower priority lines In bus mastering, only current master can interrupt Example ‐ PC Bus: 80x86 has one interrupt line 8086 based systems use one 8259A interrupt controller 8259A has 8 interrupt lines
- 21. Dr. Sudip Roy 21 Intel 82C55A: Programmable Peripheral Interface
- 22. Dr. Sudip Roy 22 Intel 82C55A: Programmable Peripheral Interface