string(88) ‘ and scans and writes to those addresses are construed as instructions to the I/O device\. ‘
INPUT/OUTPUT ORGANIZATION • Accessing I/O Devices • I/O program • Input/output mechanism Memory-mapped I/O y pp as well as Programmed I/O Interrupts Immediate Memory Gain access to • Busses Synchronous Coach Asynchronous Bus I/O in CO and O/S • • • Programmed I/O Interrupts DMA (Direct storage Access) A bus is actually a shared connection link, which uses a single, set of cables to connect multiple subsystems. The two major advantages of the tour bus organization will be versatility and low cost. Accessing I/O Equipment Most modern pcs use solitary bus layout for connecting I/O devices to CPU , Memory • The shuttle bus enables all the devices connected to it to change information • Bus consists of 3 group of lines: Address, Data, Control • Processor chip places a certain address (unique for a great I/O Dev.
) upon address lines • System which recognizes this talk about responds to the commands released on the Control lines • Processor asks for for either Read / Write • The data will be placed on Data lines Components to connect I/O devices to b t bus Interface Circuit – Address Decodierer – Control Circuits – Data signs up – Status registers • The Subscribes in I/O Interface – buffer and control • Flags in Status Subscribes like DESPROVISTO, SOUT Registers, SIN • Data Registers, like Data-IN, Data-OUT I/O interface to get an input device Memory space Address Processor chip Data Control Address Add Decoders Control C to l brake lines Data deb t big t D big t and status registers I/O /O Software Input system (s) s ( ) Input End result mechanism l i • Memory mapped I/O • Programmed I/O • Stops • DMA (Direct memory space Access)
A bus generally contains some control lines and a couple of data lines. The control lines are accustomed to signal asks for and acknowledgments, and to suggest what type of information is for the data lines. The control lines are more comfortable with indicate what the bus contains and to put into action the coach protocol. The info lines with the bus carry information involving the source and the destination. This information may consist of data, complex commands, or addresses. Busses are usually classified since processor-memory di i ll l ifi d buses or I/O buses or special purposed buses (Graphics, etc . ).
Processor memory space buses happen to be short, generally high speed, and matched to the memory system so as to improve memoryprocessor bandwidth. I/O n buses, w contrast, could be lengthy, may have many simply by t big t b t th l types of devices attached to them, and sometimes have a number of in the data bandwidth with the devices linked to them. I/O buses do not typically user interface directly to the memory although use whether processor-memory or a backplane coach to connect to memory. The major disadvantage of a bus is the fact it creates a communication bottleneck possibly constraining the maximum I/O bottleneck, throughput.
When I/O must pass through a single tour bus, the bus bandwidth of these bus limitations the maximum I/O throughput. Reason why b R h shuttle bus d i actually design is really difficult: i diffi luxury touring , the ideal bus velocity is largely limited by physical factors: the length of the bus and the number of products. These physical limits prevent us coming from running the bus randomly fast. , In addition , the requirement to support a number of devices with generally varying latencies and data transfer rates also makes shuttle bus design difficult. , it is difficult to manage many parallel wires for high speed because of clock skew and expression reflection.
The 2 basic schemes for connection on the tour bus are synchronous and asynchronous. If a bus is synchronous (e. g. Processor-memory), it provides a clock in the control lines and a fixed protocol for conversing that is in accordance with the clock. g This type of process can be executed easily in a small finite state machine. As the protocol is usually predetermined and involves tiny logic, the bus may run extremely fast and the program logic will be small. Synchronous buses possess two major disadvantages: , First, every device around the bus must run at the same clock rate. Second, because of clock alter problems, synchronous buses may not be long if they happen to be fast. An A asynchronous m h bus i not clocked. It might accommodate a is big t l k d d t wide variety of devices, plus the bus can be lengthened without worrying about clock skew or perhaps synchronization problems. To organize the indication of data between sender and receiver, a great asynchronous shuttle bus uses a handshaking protocol. Three special control lines required for hand-shaking: ReadReq: Used to reveal a browse request for recollection. The talk about is place on the data lines at the same time.
DataRdy: Used to i di t a t a d capital t D to Rd U d to point that the info word has become ready around the di d th data lines, asserted by: Output/Memory and Input/I_O Device. Ack: Used to accept the ReadReq or the DataRdy signal of the other party. I/O Dev. Memory space Steps following the device alerts a demand by bringing up ReadReq and putting the address within the Data lines: 1 . Once memory views the ReadReq line, that reads the address in the data tour bus and raises Ack to point it has been noticed. 2 . Because the Ack line is high , I/O emits the ReadReq and data lines. g / queen 3.
Storage sees that ReadReq can be low and drops the Ack collection to acknowledge the ReadReq signal (Mem. Reading happening now). some. This step starts when the storage has the info ready. It places your data from the browse request on the data lines and increases DataRdy. a few. The I/O device perceives DataRdy, reads the data in the bus, and signals that it has the data by increasing Ack. 6th. On the Ack signal, M/M drops DataRdy, and emits the data lines. 7. Finally, the I/O device, seeing DataRdy move low, drops the Ack line, signifies that the transmitting is completed. Memory mapped I/O I/O devices and the memory share similar address space the space, arrangement is called Memory-mapped I/O. In Memory-mapped I/O portions of address space are assigned to I/O devices and reads and writes to those addresses will be interpreted because commands for the I/O unit.
When the cpu places the address and data on the memory tour bus, the storage system ignores the procedure because the treat indicates some of the memory space used for I/O. The device controller, however , views the operation, records the information, and sends it for the device like a command. End user programs are p g g averted from issuing I/O g / businesses directly as the OS will not provide use of the treat space designated to the I/O devices and so the addresses are shielded by the addresses translation. Recollection mapped I/O can also be used to transmit info by composing or reading to select tackles.
The device uses the treat to determine the sort of command, plus the data could possibly be provided by a write or obtained with a read. An application request usually requires several separate I/O operations. Furthermore, the processor chip may have to question the status of the unit between specific commands to ascertain whether the command completed effectively. DATAIN DATAOUT STATUS CONTROL 7 six 5 4 DIRQ KIRQ DEN KEN SOUT DESPROVISTO 3 2 1 zero I/O procedure involving computer keyboard and display devices Signs up: DATAIN, DATAOUT, STATUS, CONTROL Flags: SIN, SOUT , Provides position information to get keyboard nd display unit KIRQ, DIRQ – Keyboard, Screen Interrupt ask for bits DEN, KEN –Keyboard, Display Allow bits Developed I/O • CPU has direct control of I/O – S Realizing status i actually t big t – Read/write commands – Transferring info • CPU waits pertaining to I/O component to complete operation • Wastes CPU time In this case, use dedicated I/O recommendations in the processor. These I/O instructions may specify the two device number and the command word word (or the location with the command word in memory). The processor chip communicates the product address by way of a set of cables normally included as part of the I/O bus.
The actual command can be transmitted within the data lines in the bus. bus (example , Intel IA-32) IA-32). By making the I/O recommendations illegal to execute when not in kernel or boss mode end user programs can be mode, eliminated from getting at the gadgets directly. The process of periodically looking at status bits to see if its about time for the next I/O operation, is called polling. Polling is the simplest way for a great I/O gadget to communicate with the processor processor. The I/O device simply sets the information within a Status enroll, register and the processor need to come and get the info.
The processor is totally in charge and does all of the checking. A ISA program to study one line in the keyboard, retail store it in memory stream and indicate it back to the display stream, The disadvantage of polling is the fact it can waste a lot of processor time because cpus are so considerably faster than I/O devices gadgets. The processor may browse the Status register many times, learn that the unit has not however completed a relatively slow I/O operation, or that the mouse has not budged since the last time it absolutely was polled.
If the device completes an operation, we need to still look at the status to determine whether that (I/O) was successful. Cost to do business in a polling interface lead to the invention of interrupts to notify the processor when an I/O gadget requires attention from the processor. Interrupt-driven I/O, Interrupt driven I/O employs I/O interrupts to indicate to the processor that an I/O unit needs attention. When a device wants to notify the processor that it provides completed several operation or needs attention, it triggers the processor chip to be cut off.
Interrupts I/O INTERRUPT Processor • The moment I/O Device is ready, it sends the INTERRUPT signal to processor by way of a dedicated controller line • Using disrupt we are preferably eliminating WAIT period • In response for the interrupt, the processor executes the Interrupt Service Routine (ISR) • Every one of the registers flags program counter-top values happen to be saved registers, flags, by the processor just before running ISR • Time required to conserve status , restore bring about execution expense? “Interrupt Latency” p con nterrupt-acknowledge transmission , I/O device interface p con accomplishes this by performance of an instructions in the interrupt-service routine (ISR) that has access to a status or data signup in the gadget interface, withought a shadow of doubt informs the device that their interrupt demand has been identified. IRQ signal is then removed by system. ISR can be described as sub-routine – may participate in a different end user than the a single being carried out and then halted. The condition code flags and the contents of any signs up used by both the interrupted software and the interrupt-service interrupt service routine are saved and restored restored.
The concept of interrupts is used in operating systems and i many control applications, where finalizing of d in t li we h my spouse and i f specific routines should be accurately timed relative to external events (e. g. current processing). Interrupt Hardware l Pull up Pullup resister INTR = INTR1 +….. +INTR n INTR An equivalent routine for a drain coach used to put into practice a open-drain common interrupt-request line Disrupt Hardware Supply pp y R INTR Processor Pullup resister INTR 1 INTR 2 INTR 3 INTR = INTR1 +….. +INTR n GND INTR Permitting and Devastating Interrupts System activates interrupt signal collection and waits with this kind of signal triggered until cpus attends • The disrupt signal range is effective during delivery of ISR and right up until the device induced interrupt is definitely serviced • Necessary to ensure that the lively signal will not lead to effective interruptions (level-triggered input) creating (level triggered the system to fall in unlimited loop. • What if a similar d my spouse and i h they would device we interrupts again, within an ISR? i my spouse and i hi • Three techniques of Controlling Stops (single device) – Disregarding interrupt – Disabling stops – Special Interrupt demand line Ignoring Interrupts – Processor hardware ignores the interrupt demand line until the execution with the first teaching of the ISR completed – Using an interrupt disable instruction following your first teaching of the ISR – no more interrupts – A return by interrupt teaching is completed before further distractions can occur • Disabling Stops – Processor chip automatically disables interrupts before starting the execution of the ISR – The processor will save the contents of LAPTOP OR COMPUTER and PS (status register) before carrying out interrupt devastating. The interrupt-enable is set to 0 – no further interrupts allowed – When go back from disrupt instruction is usually executed the contents in the PS will be restored in the stack, plus the interrupt permit is set to at least one • Unique Interrupt series p l – Special interrupt obtain line for which the interrupt handling circuit responds only t a l pada h dli i it d l to the top rated of deb f the signal – Edge –triggered g fjeofj – Processor receives only 1 request however long the queue is activated – And separate we t Simply no t disrupt di bli t disabling i to instructions ti
The sequence of situations involved in managing an interrupt request coming from a single gadget. Assuming that stops are empowered, the following is an average scenario: 1 ) 1 The product raises an interrupt ask for request. 2 . The processor chip interrupts this software currently being accomplished. t m 3. Interrupts are handicapped by changing the control bits inside the PS (except in the case of edge-triggered interrupts) interrupts). 4. The product is knowledgeable that it is request have been recognized, and in response, it deactivates the interrupti g di m ti to th we t to request transmission.. The action requested by interrupt is performed by the interrupt-service routine. 6th. Interrupts happen to be enabled and execution of the interrupted program is started again. Handling Multiple Devices • Multiple equipment can initiate interrupts g p • They uses the common interrupt request series y s q • Techniques are q – Polling – Vectored Interrupts p – Interrupt Having their nests – Daisy Chaining sumado a g Polling Scheme • The IRQ (interrupt request) bit in the status sign-up is set each time a device can be requesting a great interrupt. The Interrupt utility routine polls the I/O equipment connected to the bus. • The first system encountered while using IRQ little set is definitely serviced plus the subroutine is usually invoked. • Easy to put into practice, but a lot of time spent on exploring the IRQ bits of all devices, though some devices will not be requesting service. Vectored Interrupts • Unit requesting an interrupt determines itself directly to the cpu • The product sends a particular code for the processor over the bus. The code contains the – identification of the device device, – starting talk about for the ISR, – address of the branch for the ISR • PC discovers the ISR address from the code. • To add overall flexibility for multiple devices , corresponding ISR is accomplished by the cpu using a part address towards the appropriate schedule , system specified Disrupt Vector. A great interrupt vector is the memory space address of an interrupt handler, or a catalog into an array called a great interrupt vector table or perhaps dispatch desk , a table of interrupt vectors (pointers to routines that handle interrupts).
Interrupt vector tables retain the memory tackles of disrupt handlers. For the interrupt is generated, the processor saves its setup state by way of a context change, and starts execution with the interrupt handler at the disrupt b i ti n th we t t h dl t th i capital t t vector. The Disrupt Descriptor Desk ( s p (IDT) is certain to the ) p I386 architecture. This tells in which the Interrupt Service Routines (ISR) are located. Every single interrupt number is reserved for a specific purpose. For example , sixteen of the vectors are available to the 18 IRQ lines.
Q About PCs, the interrupt vector table (IVT or IDT) consists of 256 4-byte pointers , the first thirty-two (0-31 or 00-1F) which are appropriated f for processor exclusions, the rest farreneheit for hardware interrupts, computer software interrupts. This kind of resides inside the first 1 K of addressable recollection. Interrupt Having their nests • Pre-Emption of low priority Disrupt by another high Pre Emption concern interrupt is called Interrupt having their nests. • Pada bli Devastating I to Interrupts m i big t during th execution of th ISR the usted f the may not favour devices which usually need immediate attention. Need a priority of IRQ gadgets and accepting IRQ from a high goal device. • The top priority level of the processor may be changed y y dynamically. • The privileged instructions write inside the PS (processor status word) that encodes the cpus priority word), priority. Interrupt Nesting (contd. ) Pro ocessor INTR1 Device one particular INTA 1 Device a couple of INTRp… Unit p INTA p Top priority arbitration outlet • Managing I/O devices in a prioritized structure. g g as well as p • Each of the interrupt-request lines can be assigned a different sort of priority level level. • The processor is cut off only with a high goal device. Daisy Chaining • • • • The interrupt request line INTR is common to all the products The disrupt acknowledgement line INTA is connected to gadgets in a DAISY CHAIN method INTA propagates serially through the devices Gadget that is electrically closest for the processor gets high hello there h priority i i Low goal device may have a danger of MALNOURISHMENT INTR P Processor 3rd there�s r Device G i one particular INTA Device D i 2 .. Device n Deb i Daisy Chaining with Priority Group • • Combining Daisy chaining and Interrupt nesting to form p priority group yg g Each group has several priority levels and within each group devices happen to be connected in daisy chain way
INTR1 Proc cessor Device one particular Device you INTA one particular INTR g…. Device Deb i 1 INTA l Priority settlement circuit System D my spouse and i 1 Layout of goal groups Direct Memory Gain access to (DMA) • For I/O transfer, Processor determines the status of I/O devices, by – – Polling Waiting for Interrupt signal • Considerable cost to do business is incurred in over I/O transfer processing • To transfer large obstructs of data at high Speed, between EXTERNAL products , Working memory, DMA procedure is often employed • DMA controller permits data transfer immediately between I/O device g i and d Storage, M with i l minimal we l input i we of f processor. Direct Memory Access (DMA) • DMA control mechanism acts as a Cpu, but it can be controlled by CPU • To trigger transfer of any block of words, the processor sends the following info to control mechanism – The starting addresses of the memory space block – The word count h g – Control to designate the mode of copy such as browse or write – A control to start the DMA transfer • DMA control mechanism performs the requested I/O operation and sends a interrupt towards the processor upon completion one particular Status and Control Starting address Phrase count In?? IRQ 30 IE 1 R/W 0 Carried out DMA software g g First sign-up stores the starting address Second sign-up stores Term count Third register includes status and control flags Bits and Flags R/W Done IRQ IE one particular READ Data transfer finishes Disrupt request Raise interrupt (enable) after Data Transfer 0 PUBLISH Processor Main memory Disk/DMA control DMA controller Printer Computer keyboard Disk Drive Network Program Use of DMA Controller within a computer system Recollection accesses by processor and DMA Control mechanism are interwoven • DMA devices possess higher goal then processor over SHUTTLE BUS control • Cycle Robbing: – DMA Controller “steals” memory cycles from processor, though cpu originates the majority of memory get. • Block or Broken mode: – The of data without being interrupted • Disputes in DMA: , Processor chip and DMA, , Two DMA controllers, try to use the Bus concurrently to access the key memory DMA controller might given exclusive access to the primary memory to transfer a block
DMA and Interrupt Breakpoints During D we an My spouse and i t Teaching Cycle usted C l Bus Arbitration • Coach master: system that starts data transfers on the tour bus. • The next device may take control of the bus following your current master relinquishes control • Coach Arbitration: method by which another device for being master is usually selected • Centralized and Distributed Settlement BBSY S Processor l BR BG1 DMA control mechanism 1 BG2 DMA control 2 A basic arrangement to get bus arbitration using a daisy chain BAYERISCHER RUNDFUNK (bus obtain ) line , open up drain collection , the signal within this line is a logical OR PERHAPS of the coach request by all the g q DMA devices – BG (bus grant) collection , processor chip activates this kind of line indicating (acknowledging) for all the DMA devices (connected in daisy chain fashion) that the TOUR BUS may be used once its totally free free. – BBSY (bus busy) line , open collector line , the present bus grasp i di b implies d we devices that i i presently using they would it is l i the bus by simply signaling this kind of line BBSY Processor BAYERISCHER RUNDFUNK BG1 DMA controller 1 BG2
DMA controller two Sequence of signals during data transfer of bus mastership • Central Arbitration – Separate product (bus settlement circuitry) coupled to the bus – Processor can be your bus master, unless it grants shuttle bus mastership to DMA Intended for the timing/control, in past slide: DMA controller 2 requests and acquires coach mastership sometime later it was releases the bus. During its tenure as the bus grasp, it may execute one or more data transfer operations, depending on whether it is g, p g operating in the cycle thieving or prevent mode.
After it launches the coach, the processor resumes bus mastership. • Distributed Arbitration – Almost all devices holding out to use the bus must carry out the arbitration procedure , simply no central arbiter – Each device within the bus is definitely assigned with a identification quantity 4-bit – One or more devices request the bus by simply asserting q y g the start-arbitration signal make their identification number for the four open collector lines – ARB0 through ARB3 are the four open collector lines – One among the four is definitely selected making use of the code for the lines and one with all the highest IDENTIFICATION number
A distributed arbitration scheme Imagine two equipment, A and B, having ID amounts 5 and 6, respectively, are requesting the use of the coach. Device A transmits the pattern 0101, and unit B transmits the routine 0110. s The code seen by simply both devices is 0111. Each gadget compares the pattern on the arbitration lines to its ID, beginning with the most significant tad. If it detects a difference any kind of time bit position, it disables its motorists at that little bit position and for all lower-order bits. It can do so simply by placing a zero at the insight of these motorists drivers.
When it comes to our model, device A detects a difference on line IT I. Therefore, it disables its drivers on diff li I actually H i actually di bl i d i lines ARB one particular and ARBO. This triggers the style on the settlement lines to alter to 0110, which means that N has gained the legislation. Universal Dram�n Bus (USB) The UNIVERSAL SERIAL BUS supports two speeds of operation called lowoperation, low speed (1. 5 megabits/s) and full-speed (12 megabits/s). The Th most recent revising of the bus specification (USB i i actually f they would b ifi i installment payments on your 0) introduced a third rate of operation, called excessive (480 megabits/s).
The UNIVERSAL SERIES BUS has been designed to meet a lot of key objectives: -P Provide a simple, cheap, and easy to work with interconnection id i t l t d capital t i capital t ti program that prevails over the difficulties due to the limited number of I/O jacks available on a computer , Support a wide range of data transfer characteristics to get I/O products, including mobile phone and Internet connections /, g p , Enhance consumer convenience by using a “plug-and-play” method of operation USB Bandwidths: A low-speed rate of just one. 5 Mbit/s (~183 kB/s) is defined by UNIVERSAL SERIAL BUS 1 . 0.
It is intended primarily to save cost in lowbandwidth man interface devices (HID) including keyboards, ( ) sumado a, mice, and joysticks. The full-speed rate of doze Mbit/s (~1. 43 MB/s) is the full speed ( 1 . 43 basic UNIVERSAL SERIES BUS data rate defined simply by USB 1 . 1 . Almost all USB hubs support full-bandwidth. A high speed (USB installment payments on your 0) rate of 480 Mbit/s (~57 MB/s) was introduced in 2001. Almost all hi-speed products are capable of falling back to full bandwidth procedure if necessary, they are full-bandwidth backwards compatible. Connectors are identical. SuperSpeed ( d (USB 3. 0) rate produces upto 4800 Mbit/s ) d drone / (~572 MB/s or 5 Gbps)
Each client of the woods has a gadget called a hub, which acts as an more advanced control point between the web host and the I/0 devices products. At the root of the tree, a root hub connects the complete tree to the host computer system. The leaves of the woods are the I/0 p as well as devices becoming served. The tree composition enables a large number of devices being connected while using only basic point-topoint serial links. Each hub provides a number of plug-ins where gadgets may be connected, including other hubs. In normal operation, a link g clones a message that this receives from its upstream link with all their downstream plug-ins.
As A an outcome, a message dispatched b the host computer is luxury touring t by th they would t big t i transmission to all I/O devices, nevertheless only the addressed device will certainly respond to that message. A note from a great I/O unit is directed only upstream towards the reason behind the forest and is not really seen by simply other devices. Hence, th USB enables th h t to communicate with the I/O L the bl the sponsor to i t ith th equipment, but it does not enable they to exchange their views. The USB operates firmly on the basis of polling. A device may send a note only in response to a poll message through the host number.
Hence, upstream messages tend not to encounter disputes or interfere with each other, because no two devices can send additional messages simultaneously. This restriction allows hubs to be straightforward, low-cost gadgets. USB process requires that a message transmitted on a highspeed link is actually transmitted s y for high speed, even though the ultimate recipient is a low-speed device. gadget Hence, a message intended for gadget D is definitely sent in high speed from your root hub to centre A, a forwarded by low rate to gadget D. These transfer will need a long time, where highl ti d we hi l hi l speed visitors other nodes is permitted to continue.
Every single device on the USB, unique a centre or a great I/O gadget, is assigned a 7-bit address. This kind of address is definitely local towards the USB forest and is certainly not related at all to the details used on the processor bus. A centre may have got any number of devices or various other hubs linked to it, and addresses happen to be assigned randomly. When a system is first attached to a hub, or in the next powered upon, it has the address zero. The hardware of the centre to which this gadget is connected is capable of detecting the device has become connected, and it data this f d howdy fact within i own status my spouse and i f farrenheit its information. Periodically, the host polls each hub to collect status information and pay attention to about new devices which may have been added or shut off. When the web host is up to date that a fresh device continues to be connected, connected it uses a chain of directions to send a reset signal on the corresponding hub dock, read details from the unit about its capabilities, mail configuration info to the device, and assign the device an exceptional USB address. O deb i g i a d i actually i dd Once this kind of thi pattern is completed the device begins normal operation and responds only to the new address. Read about USB protocols Isochronous traffic about USB and USB BODY
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