Programmable vliw and simd architectures for dsp and. Pipelining hardware pipelining is widely used to achieve singlecycle core throughput. C67x can execute up to 8 instructions at the same time. Jun 14, 2004 hi all, i need to do some software pipelining using code composer studio. Software pipelining inherently improves execution speed, but it may not be possible if unnecessary dependencies exist. One approach involves improving the speed of the processor. Software pipelining is a type of outoforder execution, except that the reordering is done by a compiler or in the case of hand written assembly code, by the programmer instead of the processor. Pipelining is the process of accumulating instruction from the processor through a pipeline. Since most of dsp programs are loopintensive, soft. This paper also describes a few embedded system applications where dsp plays a signific ant role. Software pipelining, as addressed here, is the problem of scheduling the operations within an iteration, such that the iterations can be pipelined to yield optimal throughput, software pipelining has also been studied under different con texts. A software pipelining algorithm of streaming applications with low. In the case of the c6200 family of dsp, there are eight functional units that can be used at the same time figure 4.
Software pipelining is an efficient tcch nique used to expose ilp for loop programs and has been widely used for current microprocessors. Software pipelining irregular loops on the tms320c6000. This module introduces the optimized software components that enable the rapid development of multicore applications and accelerate time to market using foundational software in the mcsdk. A parallel pipelined computer architecture for digital signal. Software pipelining also called blocking or block scheduling is a popular technique used to increase the throughput of an application. Software programmable dsp software pipelining platform analysis. Software pipelining for i1, i pipelining challenging. Modulo scheduling, vectorization, ilp 1 introduction. So i assume one of two things 1 a thread is somehow overwriting the memory used by another thread, and only shows up in high speed optimisation 2 or the complier performs some software pipelining that is invalid, and.
In an efficient softwarepipelined loop, where ii softwarepipelined loop body. Figure 4 reducing the rampuprampdown effect with software pipelining. To achieve peak performance, this vliw architecture relies heavily on software pipelining. For example, in the assembly line of a car factory, each specific task such as installing the engine, installing the hood, and installing the wheels is often done by a separate work station.
The microarchitecture breaks the instructions into mips like microoperations, but it complicates the design and wastes silicon. Experiments with loops taken from some practical dsp programs are conducted on popular vliw digital signal processors to verify the algorithm. Topics include c66x dsp corepac architecture, single instruction multiple data simd, memory access, and software pipelining. Citeseerx resourceconstrained software pipelining for high.
In this paper, we present a software pipelining algorithm that schedules streaming. Software pipelining can be even more memory intensive and can take 10 to 20 times the instructions of a nonpipelined loop. Software pipelining for i1, i pipelining is an important technique used in several applications such as digital signal processing dsp systems, microprocessors, etc. Dsp in embedded systems asee peer document repository. Pipelining is the process of accumulating and executing computer instructions and tasks from the processor via a logical pipeline. It allows storing and executing instructions in an orderly process. Although many hardware and software solutions have been proposed for the multiprocessing scheduling problem of dsp algorithms, none has been able to. There are many approaches for improving the execution time of an application program. A technique called software pipelining contributes the biggest boost to improving looped code performance. Exploiting vector parallelism in software pipelined. The stations carry out their tasks in parallel, each on a different car.
Accordingly, it results in speed enhancement for the critical path in most dsp systems. Unret works with the dataflow graph which describes the loop body. Software pipelining is an optimization strategy to schedule loops and functional units efficiently. Dsp applications are usually programmed in the same languages as other science and engineering tasks, such as. Software pipelining, which overlaps multiple iterations of a loop, can also largely offset the negative impact of the long latency on performance, typically in conjunction with proper loop unrolling. The book covers software and firmware design principles, from processor architectures. In example 3, the two input arrays may or may not overlap in memory. However, due to the rearrangement of the original instructions, it is often very difficult to reuse or port the code of a softwarepipelined loop to other processors. Software pipelining for throughput optimization preesm. Jouppi, performance of image and video processing with generalpurpose processors and media isa extensions, to appear in proceedings of international symposium on computer architecture26, 1999. Demystifying digital signal processing dsp programming. Often, a test must be performed beforehand which jumps to an alternative, nonsoftwarepipelined version of the loop in these cases. Combining swpgood and swppoor loops leads to a speedup of 55% hm. So, in such cases, pipelining can be combined with parallel processing to further increase the speed of the dsp system by combining parallel processing block size.
In i, some problems of software pipelining in some commercial dsp compilers are mentioned. Dsp software development techniques for embedded and realtime systems is an introduction to dsp software development for embedded and realtime developers giving details on how to use digital signal processors efficiently in embedded and realtime systems. The elements of a pipeline are often executed in parallel or in timesliced fashion. Basic instruction scheduling and software pipelining. In order to fully utilize the instruction level parallelism of vliw dsp processors, dsp programs have to be optimized by software pipelining. Pipeline is divided into stages and these stages are. Figure 1 illustrates an example of modulo software pipelining where loop iterations are initiated at a constant rate known as iteration interval ii. Dsp software and hardware tradeoffs in professional audio applications. The throughput of an application is usually limited by the latency of its critical path. Large number of pipeline stages up to 20 in pentium 4 increases branch penalty, unless the branch prediction is accurate. The power and versatility of c makes it the language of choice for computer scientists and other professional programmers. Software pipelining is an excellent method for improving the parallelism in loops even when other methods fail. It allows storing, prioritizing, managing and executing tasks and instructions in an orderly process.
Pipelining is a technique where multiple instructions are overlapped during execution. Resourceconstrained software pipelining for highlevel. Concept of pipelining computer architecture tutorial. Optimizing compilers and embedded dsp software ee times. Aes elibrary dsp software and hardware tradeoffs in. Modern dsp processors have been integrated with instructionlevel parallelism llp, which presents a challenge to exploit ilp within dsp applications. Introduction digital signal processing theory, algorithm and applications have experienced a enormous growth in the last three decades. Assembly code conversion of softwarepipelined loop between. This paper presents unret unrolling and retiming, a new approach for software pipelining with resource constraints which is suitable for highlevel synthesis of dsp systems. Software programming techniques for embedded dsp software.
In other words, at most one interiteration data dependency relationship can be present in the flow graph. Software pipelining of nested loops for realtime dsp applications. Software pipelining bug all about digital signal processing. The compiler must assume that there is an overlap and that a given load or store must be finished before the next one can be initiated. Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that. Compared to software pipelining, our approach is able to achieve an average speedup of 1.
Multicore software development kit mcsdk for keystone devices this module provides an overview of the multicore soc software for keystone i c66x dsp devices. The design runs at 168mhz bottlenecked by the dsps at synthesis stage and when running a drc the following warnings appear. The book covers software and firmware design principles, from processor architectures and basic theory to the selection of appropriate languages and basic algorithms. Hi all, i need to do some software pipelining using code composer studio. Developers often optimize their code for execution. Software pipelining irregular loops on the tms320c6000 vliw dsp. Of course, if the loop iterates less than k times at runtime, then the code must not enter the softwarepipelined version. Assembly code conversion of softwarepipelined loop. Introduction to tms320c6000 dsp optimization texas instruments. Some amount of buffer storage is often inserted between elements computerrelated pipelines include. Software pipelining is applied to a restricted set of loops, namely those containing a single fortran statement. Evaluating mmx technology using dsp and multimedia applications, proceedings of ieee micro31, dec 1998. Instructionlevel parallelism is critical in achieving realtime performance in tis vliw dsp architecture, and as such, software pipelining is a feature used to hone the cpu architecture and isa for entitlement. Achieving better code optimization in dsp designs ee times.
We evaluate our methodology using several dsp and spec fp benchmarks. Dsp software development techniques for embedded and real. Length keystone c66x dsp corepac overview this module discusses how high performance can be achieved within each c66x dsp core. Software pipelining modern computers can execute parts of many different instructions at the same time not only dsps. Complementing software pipelining with software thread. This is quite advantageous in digital signal processing, image processing and other mathematical routines that tend to be loopcentric. Some computer architectures have explicit support for software pipelining, notably intel s ia64 architecture. Software pipelining is a technique used to schedule instructions from loops mostly so that multiple iterations of the loop execute in parallel. The power and versatility of c makes it the language of choice for computer. Power optimization on the other hand is more directly proportional to performance than it is to memory.
In computing, a pipeline, also known as a data pipeline, is a set of data processing elements connected in series, where the output of one element is the input of the next one. So i assume one of two things 1 a thread is somehow overwriting the memory used by another thread, and only shows up in high speed optimisation 2 or the complier performs some. Pdf software pipelining of nested loops for realtime dsp. This material is based upon work supported by nsf career award ccr03690. Software pipelining is an efficient tcch nique used to expose ilp for loop programs and has been widely used for current. Citeseerx document details isaac councill, lee giles, pradeep teregowda. Pipelining is an important technique used in several applications such as digital signal processing dsp systems, microprocessors, etc.
In computer science, software pipelining is a technique used to optimize loops, in a manner that parallels hardware pipelining. Dsp pipelining gives no improvement its written in behavioural code, so the dsps are not instantiated explicitely. The results were that nearoptimal results can be obtained cheaply without the specialized hardware. Pipelining is a commonly used concept in everyday life. Loops for which software pipelining fails swpfail due to conditionals and calls speed up by 16% hm. Software pipelining of nested loops for realtime dsp. The tms320c6000 architecture is a leading family of digital signal processors dsps. It originates from the idea of a water pipe with continuous water sent in without waiting for the water in the pipe to come out. Emerging architectures often have support for software pipelining. Software pipelining irregular loops on the tms320c6000 vliw. This paper presents unret unrolling and retiming, a new approach for software pipeuning.
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