Alu and data-path pdf

Chapter 2 pw jw alu and data path, cpu control design 2 s ht tp s. In some cases, one of the buses may be dedicated for moving data into registers inbus, while the other is dedicated for transferring data out of the registers outbus. The control unit tells the datapath what to do, based on the instruction thats currently being executed. Mips is a 32bit machine, so most of the buses are 32bits wide. Instruction read in stage 1 is saved in instruction register. The alu is a digital circuit that provides arithmetic and logic operation. Alu, datapath and control unit computer organization and. Data path for store word sw the format for sw is the same as lw but the data path for sw is slightly di erent. All instructions use the alu after reading the registers. The functionality of the data path logic will usually be divided into blocks and this. The sum from the alu is used as the address for the data memory 5. This input has value 0 for all but 1bit alu for the least significant bit. Alu when the two buses are busy carrying the two operands.

Along with the control unit it composes the central processing unit cpu. The alu computes the sum of the retrieved register data and the signextended immediate value in bits 15. Data path for load and store combine the register file, sign extend, alu, and the data memory immediate from the instruction value of the load or store base register effective address value read from memory load value written to destination register load value to write to memory store 22 ok, now, what about branches. Get the study material and tips for upcoming gate, barc, isro, and other cs exams. Our processor has ten control signals that regulate the datapath. The control section is basically the control unit, which issues control signals to the datapath. Arithmetic logic unit alu combinational logic function input. Elec 52000016200001 computer architecture and design fall. Lecture 5 singlecycle datapath and control computer science. Add wires and possible some hardware gates, multiplexers etc to make the. Two clock cycles are needed for memory read operation. Compute the branch address using alu in case the instruction is a branch we can do this because alu is not busy aluout will keep the target address we have not set any control signals based on the instruction type yet instruction is being decoded now in the control logic.

A demonstration of a typical twoaddress microprocessor datapath, built from a threeport registerfile and a multifunction arithmeticlogic unit the instruction set of several 16bit microprocessors includes arithmetic and logic instructions that operate on two different registers socalled 2address instructions. Memory registers 6 5 5 16 32 instructions extend sign memory data 32 pc 4 32 aluop control opcode memwrite new pc value is computed it is written at next clock pulse instruction is read \fetched from memory two readreg are. Pdf design and implementation 8 bit cpu architecture on. Datapath has to compute the target address and compare two registers. It is the fundamental building block of central processing unit of a. Pcsrc is generated by anding a branch signal from the control unit with the zero signal from the alu.

Consume less power provide better performance, clock frequency. Alu control lines note here that the alu has a 4bit control line called alu operation. Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on youtube. Memory registers 6 5 5 16 32 instructions extend sign memory data 32 pc 4 32 aluop. The datapath is capable of performing certain operations on data items. Registers read reg1 read reg2 write reg write data read data2 read data1. Arithmeticlogic instructions use alu for operation execution. An arithmetic logic unit alu is a digital circuit used to perform arithmetic and logic operations. For the least significant bit less value should be sign of a b set less than slt function 0 3 r e s u l t. Program counter, register file, instruction memory, etc. Building a datapath datapath 1 courses computer science. Eecs 150 components and design techniques for digital. The subject includes machine instructions and addressing modes, alu, data.

Alu doesnt need to know all opcodeswe will summarize opcode with aluop 2 bits. Alu f2 microcode instruction register mir clock unit 41 11 11 main memory rd wr data section datapath 32 address data in 00 next 01 jump 10 inst. A datapath is a collection of functional units such as arithmetic logic units or multipliers that perform data processing operations, registers, and buses. Elec 52000016200001 computer architecture and design. In computer science engineering cse, computer organization and architecture is a set of rules that describe the capabilities and programming model of a computer. Alu result alu zero regwrite alu operation 3 datapath for rformat instructions registerregister timing 32 result aluctr clk busw regwr 32 32 busa 32 busb 5 5 5 rw ra rb 32 32bit registers rd rs rt alu clk pc rs, rt, rd, op, func clktoq aluctr instruction memory access time old value new value regwr old value new value delay through control. It is the fundamental building block of central processing unit of a computer. Elements that process data and addresses in the cpu. Data path main components design page 1 11 data path main components design 11.

The novelty of the alu is it gives high performance through the pipelining concept. Each step fetch, decode, execute, save result requires communication data transfer paths between memory, registers and alu. The data path logic is the logic as the name suggests to process the input data and generate the correct output data. It represents the fundamental building block of the central processing unit cpu of a computer. Internal to the cpu, data move from one register to another and between alu and registers. A machine has a 32bit architecture, with 1word long instructions. Peter wilson, in design recipes for fpgas second edition, 2016. In this case, the additional buffer register may be used, as one of. Introduction to the mips architecture created date. The alu, the bus and all the registers in the data path are of identical size. Multiple inputs selects one output based upon control signals singlecycle data path. Thus, all control signals can be set based on the opcode.

The isa says, the length of our every instructions will be 16 bit. Design a 32x 32 bit register file design a 32 bit arithmetic and logic unit alu 11. For more subjects like c, ds, algorithm,computer network,compiler design etc. Opcode alu op operation funct alu action alu control input lw 00 load word na add 0010 sw 00 store word na add 0010 beq 01 branch equal na subtract 0110 rtype 10 add 00 add 0010 rtype 10 subtract 10 subtract 0110 rtype 10 and 100100 and 0000 rtype 10 or 100101 or 0001 rtype 10 seton less than 101010 slt 0111. Memory, registers, adders, alu, and communication buses. Alu takes two 32 bit input and produces a 32 bit output also, sets onebit signal if the results is 0 the operation done by alu is controlled by a 4 bit control signal input. A larger datapath can be made by joining more than one datapaths using multiplexers a data path is the alu, the set of registers, and the cpus internal buses. Datapath for each step is set up by control signals that set up dataflow directions on communication buses and select alu and memory functions. Introduction to computer architecture reading assignment. Alu a l u c o n t r o l 3 alu result zero alu control function 000 and 001 or 010 add 110 subtract 111 set on less than. For this instruction the alu is used to calculate the final memory address. Designing the control units for the single cycle data path.

Lc3 data path global bus memory interface register file and alu fetch and memory address generation condition code logic control unit just one way to build the data path for this isa alternatives may. All operations including incrementation of the pc and the gprs are to be carried out in the alu. Courtesy of arvind l034 writing synthesizable verilog. Output of alu control is a 3bit signal one of ve combinations to control the alu setting alu control inputs based on 2bit aluop control and 6bit funct eld instruction aluop instruction funct desired alu control type operation eld alu action input memory 00 lw xxxxxx add 010 memory 00 sw xxxxxx add 010 branch 01 beq xxxxxx subtract 110. Datapath and control auburn engineering auburn university. Cse 141, s206 jeff brown generating alu control alu. A 4to1 mux alusrcb selects the second alu input from among. Many relatively simple cpus have a 2read, 1write register file connected to the 2 inputs and 1 output of the alu. The first two bits indicate whether a and bneed to be inverted, respectively. Rtype instructions must access registers and an alu.

Arithmetic logic unit is the hardware that performs addition, subtraction. In this video youll learn the concept of cpu organization. Aug 21, 2019 the first alu was intel 74181 implemented as a 7400 series is a ttl integrated circuit which was released in 1970. Heres a simple alu with five operations, selected by a. The first alu was intel 74181 implemented as a 7400 series is a ttl integrated circuit which was released in 1970. Pipeline floating point alu design using vhdl request pdf. These outputs must be stored in intermediate registers for future use. Thus, each 1bit alu should have an additional input called less, that will provide results for slt function.

The alu result for an address computation in stage 3 is needed as the memory address for lw or sw in stage 4. This is set according to the instruction chapter 4 the processor 17. Oepc oesp oeac oe1 oe3 oead oeop oe2 oembr oemar oe4 oe5 setalu oemem setshft oe6 oe7 clkmem writeread mar pc sp ac mbr iropcode iraddress status ir cu control lines alu memory incpcloadpc figure3. Datapath is all about the flow of data from instruction memory to registers, alu, data memory, program counter and the other components of hardware where appropriate data needs to go. Alu s operation based on instruction type and function code e. The microarchitecture consists of the control unit and the pro grammervisible registers, functional units such as the alu, and any additional registers that may be. Arithmetic logic unit alu design presentation f cse 675. Alu, datapath and control unit computer organization. Total 7 questions have been asked from alu, datapath and control unit topic of computer organization and architecture subject in previous gate papers.

Datapath and control introduction clock cycle time and number of. The data at the specified address is fetched from memory and written into the register file at the destination specified in bits 20. Bus bus consists of 1 or more wires real computer has multiple buses, for example. Otherwise they will be lost after the next clock cycle. A complete datapath for r type instructions what else is. A 2to1 mux alusrca sets the first alu input to be the pc or a register. Remember subtractis implemented as add thus the inversion alu control lines function 0000 and 0001 or 0010 add 0110 subtract 0111 set. Computer organization and architecture notes for gate. Register transfer and datapath structures ryerson university. A modern cpu has very powerful alu and it is complex in design. Alu computes sum of base address and signextended o. Datapath for each step is set up by control signals.