I/O module :
I/O module interfaces to the systems bus or central switch and controls one or more peripheral devices.An I/O module is not simply a set of mechanical connectors that wire a device into the systems bus.rather the I/O module contains logic for performing a communication function between the peripheral and the bus.
Discuss the function of I/O module :
This module has two major functions
< Interface to the processor and memory via the syetem bus or control switch.
Interface to one or more peripheral devices by tailo red data links.
Interrupt is any infrequent or exceptional event that cause a cpu to temporarily transfer control from its current programm to another program.Interrupts are the primary means by which I/O devices obtain the services of the cpu.
Interrupts are the primary means by which I/O devices obtain the service of the cpu.
Discuss the step for interrupt service routine :
*The cpu identifies the source of the interrupt for example by polling I/O device.
*The cpu obtain the memory address of the required interrupt handler.This address can be provided by the interrupting device its interrupt request.
*The program counter pc and other cpu status information are saved as in as subroutine call.
*The pc is loaded with the address of the interrupt handler.Exception proceeds until a return instruction is encountered which transfer control back to the interrupted program.
A bus is a communication path way connecting two or more devices..Bus is shared transmission medium.A bus consists of multiple communication on pathways or lines.Each line is capable of transmitting signal is representating binary 1 and binary 0.
Example : an 8-bit unit of data can be transmitted over eight bus lines.
Significant of IO interface :
*There are a wide variety of peripherals with various methods of operation.It would be impractical to incorporate the necessary logic within the processor to control a range of devices.
*The data transfer rate of peripherals is often much slower than that of the memory or processor.Thus, it is impractical to use the high speed system bus to communicate directly with a peripheral.
On the other hand, the data transfer rate of some peripherals is faster than that of the memory or processor.Again, the mismatch would lead to inefficiencies it not managed properly.
Peripherals often use different data formats and word lengths than the computer to which they are attached.
The function of DMA :
# Whether a read or write is requested, using the read or write control line between the processor and the DMA module.
#The address of the I/O device involved, communicate on the data lines.
#The starting location in memory to read from or write to, communicated on the data lines and stored by the DMA module in its address register.
#The number of words to be read or written, again communicated via the data lines and stored in the data count register.
A pipeline is a series of stages, where some work is done at each stage.The work is not finished until it has passed through all stages.This is the key to pipelining : Division of a larger task into smaller overlapping.The advantages of Pipeline :
1.Pipeline approach to improve system performance
2.Divide process into "stages" and send tasks into a pipeline
3.Overlap the subtasks of instruction fetch, decode and execute
4.All transfers simultaneous
5.One task or operation enters the pipeline per cycle
Pipeline Processing/Criteria of Pipeline :
Pipelining is a technique of decomposing a sequential process into suboperations, with each subprocess being executed in a special dedicated segment that operates concurrently with all other segments.A pipeline can be visualized as a collection of processing segments through which binary information flows.Each segment performs partial processing dictated by the way the task is partitioned.The result obtained from the computation in each segment is transffered to the next segment in the pipeline.The final result is obtained after the data have passsed through all segments.
Interface is a process to connect one device with others.In input-output organization, I/O interface provides a metho for transferring information between internal storages and external I/O devices.Peripherals connected to a computer need special communication links for interfacing them with the central processing unit.
computer architecture :
A computer architecture refers to other attributes of a computer system that are visible to a programmer or those attributes that have a direct impact on the logical execution of a program.
Example : computer architecture attriburtes includes the instruction set.the number of bits used to represent difference data types, I/O mechanisms, and techniques for addressing memory.
Discuss the functional units of a computer :
Data Processing : The computer must be able to process data.The data may take a wide variety of forms and the range of processing requirements is broad data storage.
Data Storage :It is also essential that a computer store data.The computer must temporarily store at least those pieces of data that are being worked on can perform the two types of data storage function that is sort term data storage and long term data storage.
Data Movement :The computer must able to move data between itself and the side world.When data are received from or delivered to a device that is directly connected the computer, the process is unknown as input and the device is referred to as a peripheral.When data is removed over longer or from a remote devices.
Control : A control unit manages the computers resources and chestrates the performance of its functional parts in response to those instructions.
An instruction manuipulate the stored data and a sequence of instruction constitutes a program.In general an instruction has two components 1.Op-code field 2.Address field(S)/operand Example : ADD R1, R2 op-code operandDiscuss the cpu's processing steps of an instruction :
Data Processing :Arithmetic and logic instruction arithmetic instruction provide computational capabilities for processing numeric data logic instruction operate the bits of a word as bits rather than as number logic instruction thus provid capabilities for processing any other type of data.There operations are performed primary on data in cpu register. Data Storage :Memory instruction are used for moving dta between memory and cpu register. Data Movement : I/O instruction are needed to transfer program and data into memory from storage device or input and the result of computation back to the user. Control/Test and Branch Instruction :Test instruction are used to test the value of a data word or the status as a computation.Branch instruction are then used to a different set of instruction depending on the decision module.
Every computer contains several types of devices to store the instruction and data required for its operation.These storage devices are called memory or computer memory.Different between RAM and ROM :
RAM ROM 1.RAM stands for random access memory. 1.ROM stand for read only memory 2.User can read and erite into it.. 2.User can only read from it. 3.For any type of processing user must store program and data into RAM 3.Manufacture stores instruction into the ROM permanently 4.RAM is volatile memory 4.ROM is non-volatile memory 5.Information is lost when router the power is switched off 5.Information are not lost when the power is switched off.
we can measure the cost and performance of a memory :
There are three parameter are in the cost and performance of a memory : - Access time :- For random access memory, this is the tiime it takes to perform a read or write operation that is , the time from the instant that an address is presented to the memory to the instant that data have been stored or made available for access time is the time it takes to position the read, write mechanism at the finished location.
Memory Cycle Time :- This concept is primary applied to random access memory and consists if the access time plus any additional time required before a second access can commence meomory cycle time is concerned with the system bus not the processor.
Transfer Rate :- This is the rate at which data can be transferred into or out of a memory unit.For random access memory, it is equal to 1/cycle time.
For non-random access memory, the following relationship holdes -
TN = TA +n/R.
Where TN = Average time to read or write N bits.
TA = Average access time.
N = Number of bits
R = Transfer rate in bits per second(bps).