01-11-2012, 04:30 PM
INPUT-OUTPUT ORGANIZATION
INPUT-OUTPUT.ppt (Size: 558.5 KB / Downloads: 34)
INPUT/OUTPUT INTERFACE
Provides a method for transferring information between internal storage (such as memory and CPU registers) and external I/O devices
Resolves the differences between the computer and peripheral devices
Peripherals - Electromechanical Devices
CPU or Memory - Electronic Device
Data Transfer Rate
Peripherals - Usually slower
CPU or Memory - Usually faster than peripherals
Some kinds of Synchronization mechanism may be needed
Unit of Information
Peripherals – Byte, Block, …
CPU or Memory – Word
Data representations may differ
I/O BUS AND MEMORY BUS
* MEMORY BUS is for information transfers between CPU and the MM
* I/O BUS is for information transfers between CPU
and I/O devices through their I/O interface
* Many computers use a common single bus system
for both memory and I/O interface units
- Use one common bus but separate control lines for each function
- Use one common bus with common control lines for both functions
* Some computer systems use two separate buses,
one to communicate with memory and the other with I/O interfaces
- Communication between CPU and all interface units is via a common
I/O Bus
- An interface connected to a peripheral device may have a number of
data registers , a control register, and a status register
- A command is passed to the peripheral by sending
to the appropriate interface register
- Function code and sense lines are not needed (Transfer of data, control,
and status information is always via the common I/O Bus)
HANDSHAKING
Strobe Methods
Source-Initiated
The source unit that initiates the transfer has
no way of knowing whether the destination unit
has actually received data
Destination-Initiated
The destination unit that initiates the transfer
no way of knowing whether the source has
actually placed the data on the bus
To solve this problem, the HANDSHAKE method
introduces a second control signal to provide a Reply
to the unit that initiates the transfer
PRIORITY INTERRUPT
Priority
- Determines which interrupt is to be served first
when two or more requests are made simultaneously
- Also determines which interrupts are permitted to
interrupt the computer while another is being serviced
- Higher priority interrupts can make requests while
servicing a lower priority interrupt
Priority Interrupt by Software(Polling)
- Priority is established by the order of polling the devices(interrupt sources)
- Flexible since it is established by software
- Low cost since it needs a very little hardware
- Very slow
Priority Interrupt by Hardware
- Require a priority interrupt manager which accepts
all the interrupt requests to determine the highest priority request
- Fast since identification of the highest priority
interrupt request is identified by the hardware
- Fast since each interrupt source has its own interrupt vector to access
directly to its own service routine
INPUT/OUTPUT PROCESSOR - CHANNEL
Channel
- Processor with direct memory access capability
that communicates with I/O devices
- Channel accesses memory by cycle stealing
- Channel can execute a Channel Program
- Stored in the main memory
- Consists of Channel Command Word(CCW)
- Each CCW specifies the parameters needed
by the channel to control the I/O devices and
perform data transfer operations
- CPU initiates the channel by executing an
channel I/O class instruction and once initiated,
channel operates independently of the CPU
INPUT-OUTPUT.ppt (Size: 558.5 KB / Downloads: 34)
INPUT/OUTPUT INTERFACE
Provides a method for transferring information between internal storage (such as memory and CPU registers) and external I/O devices
Resolves the differences between the computer and peripheral devices
Peripherals - Electromechanical Devices
CPU or Memory - Electronic Device
Data Transfer Rate
Peripherals - Usually slower
CPU or Memory - Usually faster than peripherals
Some kinds of Synchronization mechanism may be needed
Unit of Information
Peripherals – Byte, Block, …
CPU or Memory – Word
Data representations may differ
I/O BUS AND MEMORY BUS
* MEMORY BUS is for information transfers between CPU and the MM
* I/O BUS is for information transfers between CPU
and I/O devices through their I/O interface
* Many computers use a common single bus system
for both memory and I/O interface units
- Use one common bus but separate control lines for each function
- Use one common bus with common control lines for both functions
* Some computer systems use two separate buses,
one to communicate with memory and the other with I/O interfaces
- Communication between CPU and all interface units is via a common
I/O Bus
- An interface connected to a peripheral device may have a number of
data registers , a control register, and a status register
- A command is passed to the peripheral by sending
to the appropriate interface register
- Function code and sense lines are not needed (Transfer of data, control,
and status information is always via the common I/O Bus)
HANDSHAKING
Strobe Methods
Source-Initiated
The source unit that initiates the transfer has
no way of knowing whether the destination unit
has actually received data
Destination-Initiated
The destination unit that initiates the transfer
no way of knowing whether the source has
actually placed the data on the bus
To solve this problem, the HANDSHAKE method
introduces a second control signal to provide a Reply
to the unit that initiates the transfer
PRIORITY INTERRUPT
Priority
- Determines which interrupt is to be served first
when two or more requests are made simultaneously
- Also determines which interrupts are permitted to
interrupt the computer while another is being serviced
- Higher priority interrupts can make requests while
servicing a lower priority interrupt
Priority Interrupt by Software(Polling)
- Priority is established by the order of polling the devices(interrupt sources)
- Flexible since it is established by software
- Low cost since it needs a very little hardware
- Very slow
Priority Interrupt by Hardware
- Require a priority interrupt manager which accepts
all the interrupt requests to determine the highest priority request
- Fast since identification of the highest priority
interrupt request is identified by the hardware
- Fast since each interrupt source has its own interrupt vector to access
directly to its own service routine
INPUT/OUTPUT PROCESSOR - CHANNEL
Channel
- Processor with direct memory access capability
that communicates with I/O devices
- Channel accesses memory by cycle stealing
- Channel can execute a Channel Program
- Stored in the main memory
- Consists of Channel Command Word(CCW)
- Each CCW specifies the parameters needed
by the channel to control the I/O devices and
perform data transfer operations
- CPU initiates the channel by executing an
channel I/O class instruction and once initiated,
channel operates independently of the CPU