The top level view is important because of its explanatory power in understanding about the nature of computer.
Hardwired programs – process of connecting the various components in the desired configuration as a form of programming. CPU execution and storing concept dito pumapasok ung mga techniques ng processor example ay branch prediction
In figure (a) programming in hardware the system accepts data and control signals and produce results while, in figure(b) it indicates two major components of a system: an instruction interpreter and a module of general purpose of arithmetic and logic functions. Kailangan pa ng instruction codes tas ay interpret para maging control signal saka pa papasok sa ALU at logic functions saka pa ang result.
Inputs are the signals or data received by the system, and outputs are the signals or data sent from it. Moves data between the computer and its external environment.
The CPU exchanges data from memory with the use of MAR(memory address registers) which specifies the address in memory for the next read or write, and a MBR(memory buffer register) which contains the data. Similar to an IOAR specifies a particular I/O device and an IOBR used for exchange data between I/O module and the CPU.
Report in SAD
A Top-Level View ofComputer Functionand Interconnection
• This chapter focuses on the basic structures used for computer component interconnection. As background, the chapter begins with a brief examination of the basic components and their interface requirements. Then a functional overview is provided. And also examined the use of
Computer Components• The Control Unit and the Arithmetic and Logic Unit constitute the Central Processing Unit• Data and instructions need to get into the system and results out – Input/output• Temporary storage of code and results is needed – Main memory
Von Neumann Architecture• Data and Instructions are stored in a single read-write memory.• The contents of this memory are addressable by location, without regard to the type of data contained there.• Execution occurs in a sequential fashion (unless explicitly modified) from one instruction to the next.
More Components• I/O Components: a module that accepts data, and instructions and converts them into instruction signals usable by the system. It can also report results in the form of an output module.• Memory: A place to store instructions and data temporarily. (Von Neumann pointed out that the same memory could be used to store both instructions and data).
Computer Function The basic function performed by a computeris execution of a program, which consists of set ofinstructions stored in memory. The processor doesthe actual work by executing instructions specifiedin the program. This section provides an overviewof the key elements of the program execution. Inits simplest form, instruction processing consists oftwo steps: The processor reads (fetches)instructions from the memory one at a time andexecute each instruction.
Fetch Cycle• Program Counter (PC) holds address of next instruction to fetch• Processor fetches instruction from memory location pointed to by PC• Increment PC – Unless told otherwise• Instruction loaded into Instruction Register (IR)• Processor interprets instruction and performs required actions
Execute Cycle• Processor-memory – data transfer between CPU and main memory• Processor I/O – Data transfer between CPU and I/O module• Data processing – Some arithmetic or logical operation on data• Control – Alteration of sequence of operations – e.g. jump to other location
InterruptsA mechanism by which other modules may interrupt the normal processing of the processor.Classes of InterruptsProgram: Generated by some condition that occurs as a result of an instruction execution, such as arithmetic overflow, division by zero, attempt to execute an illegal machine instruction, or reference outside a user’s allowed memory space..
Interrupts (cont.)• Timer: Generated by a timer within the processor. This allows the operating system to perform certain functions on a regular basis.• I/O: Generated by an I/O controller, to signal normal completion of an operation or to signal a variety of error conditions.• Hardware Failure: Generated by failure such as power failure or memory parity error.
Interrupts.. Why bother?• Without the use of interrupts, once this command is issued, the program must wait for the I/O device to perform the requested function. The program might wait by simply repeatedly performing a test operation to determine if the I/O operation is done.
Interrupt Cycle• Added to instruction cycle• Processor checks for interrupt – Indicated by an interrupt signal• If no interrupt, fetch next instruction• If interrupt pending: – Suspend execution of current program – Save context – Set PC to start address of interrupt handler routine – Process interrupt – Restore context and continue interrupted program
PROGRAM FLOW OF CONTROLWITHOUT AND WITH INTERRUPTS
Multiple Interrupts• Disable interrupts – Processor will ignore further interrupts whilst processing one interrupt – Interrupts remain pending and are checked after first interrupt has been processed – Interrupts handled in sequence as they occur• Define priorities – Low priority interrupts can be interrupted by higher priority interrupts – When higher priority interrupt has been processed, processor returns to previous interrupt
Instruction Cycle (with Interrupts) - State Diagram
Interconnection Structure – The collection of paths connecting the various modules. The design of this structure will depend on the exchanges that must be made between modules. The computer consists of a set ofcomponents or modules of three basic types(processor, memory, I/O) that communicatewith each other. In effect, computer is anetwork of basic modules. Thus, there mustbe paths for connecting the modules.
Interconnection Structure (cont.)•Memory: Typically, a memory module willconsists of N words of equal length. Each word isassigned a unique numerical address(0,1………..N-1)•I/O module: From an internal (to the computersystem) point of view, I/O is functionally similar tomemory. Two operations: read and write.•Processor: reads in instructions and data, writesout data after processing, and uses control signalsto control overall operation of the system. It alsoreceives interrupt signals.
Buses• There are a number of possible interconnection systems• Single and multiple BUS structures are most common• e.g. Control/Address/Data bus (PC)• e.g. Unibus (DEC-PDP)
What is a Bus?• A communication pathway connecting two or more devices• Usually broadcast• Often grouped – A number of channels in one bus – e.g. 32 bit data bus is 32 separate single bit channels• Power lines may not be shown
Bus Structure•Consists from about to 50 to hundreds ofseparate lines.•Each line is assigned a particular meaningor function.•3 functional groups: – Data lines – Address lines – Control lines
Data Bus• Carries data – Remember that there is no difference between “data” and “instruction” at this level• Path for moving data between system modules.
Address bus• Identify the source or destination of data on the data bus• e.g. CPU needs to read an instruction (data) from a given location in memory
Control Bus• Control and timing information – Memory read/write signal – Interrupt request – Clock signals
Elements of Bus DesignType: Dedicated, MultiplexedMethod of Arbitration: Distributed, CentralizedTiming: Synchronous, AsynchronousBus Width : Address, DataData Transfer Type Read Write Read-modify-write Read-after-write Block
Bus Types• Dedicated – Separate data & address lines – Permanently assigned either to one function or to physical subset of computer components• Multiplexed – Shared lines – Address valid or data valid control line – Advantage - fewer lines – Disadvantages • More complex control • Ultimate performance
Method of Arbitration•Centralized – Bus controller or arbiter is responsible for allocating time on the bus.•Distributed – There is no central controller.
Timing•Synchronous -The occurrence of events on the bus is determined by a clock.•Asynchronous -The occurrence of one event on a bus follows and depends on the occurrence of previous event.
Bus Width – The width of the data bus has an impact on system performance. The wider the data bus, the greater the number of bits transferred at one time. The width of the address bus has an impact on system capacity. The wider the address bus, the greater the range of locations that can be referenced.
PCI(Peripheral Component Interconnect) Bus• is a computer bus for attaching hardware devices in a computer. The PCI bus supports the functions found on a processor bus, but in a standardized format that is independent of any particular processor. Devices connected to the bus appear to the processor to be connected directly to the processor bus, and are assigned addresses in the processors address space.
PCI Bus Lines (required)• Systems lines – Including clock and reset• Address & Data – 32 time mux lines for address/data – Interrupt & validate lines• Interface Control• Arbitration – Not shared – Direct connection to PCI bus arbiter• Error lines
PCI Bus Lines (Optional)• Interrupt lines – Not shared• Cache support• 64-bit Bus Extension – Additional 32 lines – Time multiplexed – 2 lines to enable devices to agree to use 64- bit transfer• JTAG/Boundary Scan – For testing procedures