Presented by arrash jaffarzadeh filmed by savannah silva. These resources include more loadstore, computational, and branch units, as well as larger, lowerlatency caches than would be required for a superscalar processor. Hardware and software for vliw and epic the epic approach is based on the application of massive resources. A vliw approach to architecture, compilers and tools fisher, joseph a. It has been developed by intel and hewlett packard.
Superscalar cpus use hardware to decide which operations can run in parallel at runtime, while vliw cpus use software the compiler to decide which operations can run in parallel in advance. Name dependences also exist and may be removed by renaming techniques like those we. The appendices belowsome guest authored by subject expertscover a range of topics, including specific architectures. Understanding epic architectures and implementations clemson.
It provides up to 128 general and floating point unit registers and uses speculative loading, predication, and explicit parallelism to accomplish its computing tasks. Hardware and software for vliw and epic 1 the epic approach is based on the application of massive resources. Explicitly parallel instruction computing wikimili, the. Because the complexity of instruction scheduling is moved into the compiler, complexity of hardware can be reduced. Vliw designs commonly appear in digital signal processor chips. Significantly raising the hardwaresoftware interface created an opportunity for architecture innovation. It was the basis for intel and hp development of the intel itanium architecture, and hp later asserted that epic was merely an. Instruction level parallelism static instruction scheduling. Thus, ia64gamblesthat,in thefuture, powerwillnotbethecriticallimitation,andthatmassive. Vliw is an architecture designed to help software designers extract more parallelism from their software than would be possible using a traditional risc design. Appendix h hardware and software for vliw and epic. I can say that the processor giant surrendered the bastion of the pure vliw under the pressure of software giants.
Epic explicitly parallel instruction computing is a 64bit microprocessor instruction set which is an improvement to the vliw very large instruction word architecture. Whereas conventional central processing units cpu, processor mostly allow programs to specify instructions to execute in sequence only, a vliw processor allows programs to explicitly specify instructions to execute in parallel. The compiler identifies the parallelism in the program and communicates it to the hardware by specifying which operations are independent of one another. This information is of direct value to the hardware, since it knows with no. It uses speculative loading, predication, and explicit parallelism.
Instructionlevel parallelism an overview sciencedirect. Very long instruction word vliw describes a computer processing architecture in which a language compiler or preprocessor breaks program instruction down into basic operations that can be performed by the processor in parallel that is, at the same time. Epic explicit parallel instruction computing is a form of vliw, and risc, with a few additions. The vliw and epic processor architectures school of computer. Predicate software pipeline stages single vliw instruction p1 ld r1 p2 add r3 p3 st r4 p1 bloop dynamic execution. If these speculated instruc tions were permitted to modify hardware registers or memory, the program would be in an inconsistent state. Hardware ensures that loads take exactly mlr cycles to return values into processor pipeline. Automatic architectural synthesis of vliw and epic processors shail aditya b. Basically, it uses vliw instructions, but has some hints embedded in the instruction set to help with the parallelism and to reduce branching with predication, and it has a few more registers, and some other minor changes. Vliwepic processors improve the performance by issuing multiple independent instructions based on the decision of the compiler while limiting hardware complexity. Software thread integration for converting tlp to ilp on vliwepic architectures by won so a thesis submitted to the graduate faculty of. Very long instruction word vliw, and in its generalization, explicitly parallel instruction computing epic architectures explicitly encode multiple independent operations within each instruction. Zuse z3 1941, patent filed in 1949 execution pipeline with overlap of instructions. Wikizero explicitly parallel instruction computing.
In 1970 most computation systems were equipped with additional vector signal processors using vliwlike long instructions flashed in rom. The readings section contains a list of required redaings and other optional readings for the course. Hardware support for exploiting parallelism predicate instructions. Understanding epic architectures and implementations. Founded in a basement in 1979, epic develops software to help people get well, help people stay well, and help future generations be healthier. Dynamically scheduled processors have lower cpi better performance than statically scheduled ones. Explicitly parallel instruction computing wikipedia. The vliw very long instruction word architecture is rooted in the parallel microcode used yet at the dawn of computer engineering and in control data cdc6600 and ibm 36091 supercomputers.
Static scheduling can look at the whole program rather than a relatively small instruction window. Vliw architectures achieve high performance through the combination of a number of key enabling hardware and software. But solving a difficult problem of interaction of hardware and software in the vliw architecture requires thorough preliminary investigations. Vliw and epic advocates at the time believed if a single instruction could specify, say, six independent operationstwo data transfers, two integer operations, and two floating point operationsand compiler technology could efficiently assign operations into the six instruction slots, the hardware could be made simpler. It is part two of a two part lesson that teaches you about your computers hardware and. Superscalar implementations are required when architectural compatibility must be preserved, and they will be used for entrenched architectures with legacy software, such as the x86 architecture that dominates the desktop computer market. View notes from eng at bgs institute of technology. Aca unit 8 hardware and software for vliw and epic notes unit 8 download as pdf file. Summary of discussions multiple issue ilp processors. This is intels term for vliw plus some dynamic checks. In addition, there is an extra cost in compiler development to take into account when performing a costbenefit analysis for vliw execution over hardware schedule superscalar execution. Software thread integration for converting tlp to ilp on vliw. Epic, for explicitly parallel instruction computing.
Cristina silvano the epic architecture and a noptimization, jacquesolivier haenni. An early example of the run time hardware approach is the national semiconductor swordfish processor 1990. H2 appendix h hardware and software for vliw and epic. In addition to the custom vliw processor, pico may design one or more nonprogrammable, systolicarray coprocessors asics and a twolevel cache hierarchy to support these processors. Cs 211 history introduction to explicitly parallel. Cs 211 history introduction to explicitly parallel overview. The fact that there are more embedded computers than generalpurpose computers and that we are impacted by hundreds of them every day is no longer news.
However, these concepts are more favorable for embedded systems and are not proven to be widely popular for generalpurpose computing. A vliw implementation has capabilities very similar to those of a superscalar processorissuing and completing more than one operation at a timewith one important exception. Specifying multiple operations per instruction creates a verylong instruction word architecture or vliw. In this chapter, we discuss compiler technology for increasing the amount of par allelism that we can.
An architecture for instructionlevel parallel processors michael s. It forms the interface between the hardware and the software and facilitates ef. Epic explicitly parallel instruction computing epic permits microprocessors to execute software instructions in parallel by using the compiler, rather than complex ondie circuitry, to control parallel instruction execution. Jan 16, 2014 part one of a twopart lesson teaches you about your computers hardware. A new golden age for computer architecture february 2019. Aca unit 8 hardware and software for vliw and epic notes unit. It partitions the given application between hardware the systolic arrays and software, compiles the software to.
A vliw processor allows programs that can explicitly specify instructions to be executed at the same time i. Working together, intel and hewlett packard designed a 64bit processor based on epic ideas to replace the 32bit x86. Part one of a twopart lesson teaches you about your computers hardware. Very long instruction word vliw processors 2, 3 are examples of architectures for which the program provides explicit information regarding parallelism1. Hardware support for exposing parallelism predicated instructions motivation oloop unrolling, software pipelining, and trace scheduling work well but only when branches are predicted at compile time oin other situations branch instructions can severely limit parallelism. The compiler is still responsible for scheduling instructions, but there is also speculation that can be controlled by the compiler as well as the microarchitecture. Static scheduling can look at the whole program rather than a relatively small. Aca unit 8 hardware and software for vliw and epic notes unit 8 free download as pdf file. An introduction to verylong instruction word vliw computer. Vliw of course is the most dramatic departure to the current norm in computer architecture. These include vliw very long instruction word, epic explicitly parallel instruction computing, and tta transport triggered architecture. The program is translated into primitive risc style operations. A partial list of machines and designs exploiting ilp. In this chapter we discuss compiler technology for increasing the amount of par allelism that we.
An architecture for instructionlevel parallel processors. Theseresourcesincludemoreloadstore, computational, andbranchunits, aswellaslarger, lowerlatencycachesthanwould berequiredforasuperscalarprocessor. May 03, 2015 classic vliws have a very long and rigid instruction word, with dedicated fields in that instruction word for each of the functional units. Summary of discussions ilp processors vliwepic, superscalar superscalar has hardware logic for extracting parallelism solutions for stalls etc. Pervasive from highend servers to lowend embedded systems e. A vliw processor allows programs that can explicitly specify instructions to be. It is part two of a two part lesson that teaches you about your computers hardware and software. The processors instructionset architecture isa specifies the interface between hardware and software, while. Merced was much delayed for both hardware and software reasons and currently performance is not up to what was expected. G2 appendix g hardware and software for vliw and epic. Automatic architectural synthesis of vliw and epic processors. Highend consumer devices currently include the intel itanium line of cpus known as explicitly. Harvard mark i 1944 overlap of operations a longrunning operation such as a multiply can be started and other operations such as adds or prints can run as concurrent, interposed operations before the multiply finishes and delivers.
In addition to the custom vliw processor, pico may design one or more. Hardware and software for vliw and epic directory of homes. This was intended to allow simple performance scaling without resorting to higher clock frequencies. Vliw architectures achieve high performance through the combination of a number of key enabling hardware and software technologies. Optimizing scheduler compilers static branch prediction symbolic memory disambiguation prediction execution software speculative execution program compression. Vliwepic depends on the ability of the compiler to find enough instructions. Software thread integration for converting tlp to ilp on. Pdf automatic architectural synthesis of vliw and epic. The material covered is just the general information. This paradigm is also called independence architectures. An introduction to very long instruction word vliw computer architecture, philips semiconductors advanced computer architecture, vliw arhcitectures, prof. Instructions directly control hardware with minimal decoding. Autumn 2006 cse p548 vliw 12 ia64 epic explicitly parallel instruction computing, aka vliw ia64 architecture, itanium implementation.
When a vliw instruction issues, all of the functional units receive a new instruction which may be a nop. As for vliw that can be better applied in emerging embedded applications, we have confronted several new types of processors. Transmeta provides a runtime software approach that translates x86 instructions into an internal vliw format, which they call codemorphing and which includes data and control speculation 15,16. Indeed, vliw in the large is best embodied by intels epic ia64 architecture, which is more complex than the companys sister 32bit microprocessor families.
One goal of epic was to move the complexity of instruction scheduling from the cpu hardware to the software compiler, which can do the instruction scheduling. The explicitly parallel instruction computing epic style of architecture is an evolution of vliw that has also absorbed many superscalar concepts, albeit in a for m adapted to epic. Intel and hp are betting everything they have on epic, there implementation of vliw. Epic processors retain vliws philosophy of statically exposing ilp and. Explicitly parallel instruction computing epic is a term coined in 1997 by the hpintel alliance to describe a computing paradigm that researchers had been investigating since the early 1980s. Automatic design of vliw and epic instruction formats. Classic vliws have a very long and rigid instruction word, with dedicated fields in that instruction word for each of the functional units. The appendices belowsome guest authored by subject expertscover a range of topics, including specific architectures, embedded systems, and applicationspecific processors. Jan 21, 2014 this lesson was created for ted 5110 students. The paper describes a mechanism for automatic design and synthesis of very long instruction word vliw, and its generalization, explicitly parallel instruction computing epic processor. Very long instruction word vliw processors 2, 3 are examples of. Whereas conventional processors mostly only allow programs that specify instructions to be executed one after another. Like the risc approach, vliw and epic shifted work from the hardware to the compiler. Very long instruction word vliw refers to instruction set architectures designed to exploit instruction level parallelism ilp.