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1、一种基于TMS320VC5402实现FIR滤波器的技术薛继华沈琰（东南大学无线电工程系，江苏南京210096）摘要： FIR滤波器在各种数字信号处理系统中获得了广泛应用，它总是稳定的，并且具有严格的线性相位等优点。本文首先介绍了TMS320VC5402DSP主要特性和FIR滤波器知识。然后分析了两种循环寻址数据存储器的组织方案，并给出了相应的滤波程序。最后阐述了用FIRS指令实现FIR滤波器的优点。关键词： DSP ；FIR滤波器 ；循环寻址 ；An Technology of Implementing FIR Filter based on TMS320VC5402Xue Ji-hua ,
2、Shen Yan(Department of Radio Engineering ,Southeast University, Nanjing, Jiangsu 210096,China)Abstract: FIR Filter is widely used in digital signal processing applications because its always stable, and has perfect linear phase feature. This paper first introduces the main performance of TMS320VC540
3、2 and the basic conception of FIR Filter.Then it expounds two kinds of organizations of data memory by using circular addressing mode, and programmes are presented for example.In the end , it indicates the advantage of implementing FIR filter with FIRS instruction. Key words: DSP ；FIR Filter ；Circul
4、ar Addressing ；1、前言数字信号处理就是用数字信号处理器（DSP）来实现各种算法。由于具有精度高、灵活性强等优点，已广泛应用在数字图像处理、数字通信、数字音响、声纳、雷达等领域。而数字滤波技术又是进行数字信号处理的最基本手段之一。它是对数字输入信号进行运算，产生数字输出信号，以改善信号品质，提取有用信息，或者把组合在一起的多个信号分量分离开来为目的。在许多实际应用（如：音乐信号、图像信号处理）中，为了保证滤波后的信号不产生相位失真，一般均采用FIR数字滤波器。本文选用TMS320VC5402作为DSP处理器，研究了对其配置和编程从而实现FIR滤波器的技术。2、TMS320VC54
5、02的主要特点：TMS320VC5402是TI公司于1999年10月推出的性价比极高的定点数字信号处理器（DSP）。运算速度高达100MIPS。图1是它的内部硬件组成框图，包括：CPU，总线，存储器，在片外设电路等。主要特点如下： 由一条程序总线、三条数据总线和四条地址总线构成增强型哈佛结构； 40位算术逻辑单元（ALU），包括一个40位桶形移位寄存器和两个独立的40位累加器； 17bitx17bit并行乘法器单元和一个专用的40位加法器，用于非流水线的单周期乘法/累加（MAC）操作； 比较、选择、储存单元（CSSU），用于维特比加法/比较选择； 两个地址发生器，包括8个辅助寄存器（AR0AR
6、7）和2个辅助寄存器算术单元（ARAU0、ARAU1）； 192K字16bit可寻址的存储器空间（64K字的程序空间、64K字的数据空间、64K字的I/O空间），片内提供16K双存取RAM，4K ROM； 在片外围电路包括：软件可编程等待状态发生器、片内锁相环（PLL）时钟发生器、2个多通道带缓冲串行接口（McBSP）、2个可编程的定时器等；除了上述高性能的硬件结构外，TMS320VC5402还提供了先进的指令集，实现单指令重复和块重复、32位长操作指令、具有并行存储和并行加载的算术指令、一条指令同时读2或3个操作数、从中断快速返回指令。3、FIR数字滤波器FIR滤波器实质上就是一个分节的延迟
7、线，把每一节的输出用滤波器系数进行加权累加，便得到滤波器的输出结果，它总是稳定并且可实现的。在一些工程实际应用（如：图像处理、数据调制解调）中，往往对相位要求较高。FIR滤波器可以实现严格的线性相位，从而得到了广泛应用。它的差分方程数学表达式为： （1）式中，N是FIR滤波器的抽头数，x(n)表示在n 时刻输入的信号样值，h(n)表示滤波器的第n级抽头系数。横截型FIR滤波器的结构如图2所示：4、用TMS320VC5402的MAC指令实现FIR滤波器对于给定的滤波器技术指标，利用滤波器设计软件包工具，例如MATLAB，可以确定数字滤波器系数。然后用汇编指令MAC，合理组织存储器，编程实现。4.
8、1存储器的组织TMS320VC5402定点DSP芯片提供了单周期乘法累加指令。数据可以在每个周期内经过CB和DB两数据总线传送到乘法器，并且在单个周期内完成相乘和相加，数据的地址由辅助寄存器算术单元（ARAU）提供。这样使数字滤波器每个滤波样值的计算可以在一个周期完成。假设x(n)代表了在n时刻输入到FIR滤波器的信号样值，它的冲激响应为：h(0)、h(1)、h(2)h(N-1)，则此刻滤波器的输出可表示为下式： (2)接下来借助循环寻址实现FIR滤波器，图3是TMS320VC5402进行FIR滤波时的一种有效的存储器组织方案。 在DSP的数据存储器的Page 0页中的0019H单元是循环缓冲
9、区长度寄存器BK，必须先用滤波器的长度值N来初始化。并且循环缓冲区的基地址还应满足如下条件：有效的基地址必须是M的整数倍，其中M是一个大于N且是2的整数次幂的数集合中的最小值。例如N28的循环缓冲区必须从地址000002开始，即起始地址的低5位为0。4.2用MAC指令编程实现FIR滤波器的程序片断：FILT_task1 ld Store_SICX,A STLM A,ar4 STM #1,ar0 ;间址 STM #28,bk LD DEM_Out,A STL A,*ar4+% ;输入信号:实部 STM #Coef_Tab1,ar5 ;滤波器实部系数地址 LD #0,A stm#27,brc RP
10、TBSICXU-1 MAC *AR4+0%,*AR5+,ASICXU LD A,-16,A ;低通滤波结果 LD C7FFF,B MIN A NEG B MAX A STL A,DEM_Out LDM AR4,A STL A,Store_SICX RETCoef_Tab1 .word 100 ;h(0) .word 7 ;h(1) .word -248 .word -71 ;h(N-1) .end5. 用TMS320VC5402的FIRS指令实现FIR滤波器由图2可知：输出信号序列为单位脉冲响应h(n)与输入信号序列x(n)的线性卷积。当FIR滤波器的单位脉冲响应h(n)满足以下两个条件之一，
11、就能被设计成具有精确的线性相位的滤波器。 ( 3 ) ( 4 ) 式（3）称为第一类线性相位的幅度条件（偶对称），式（4）称为第二类线性相位的幅度条件（奇对称）。在工程实践中，前者获得了广泛运用。此时滤波器的输出表达式为： (5)5.1存储器的组织要利用FIRS指令，需要将输入数据缓冲分成两个循环缓冲区来实现。每个循环缓冲区的大小为N/2，循环缓冲区1存放输入数据的前半序列，循环缓冲区2存放输入数据的后半序列。设辅助寄存器AR2用来寻址循环缓冲区1，AR3用来寻址循环缓冲区2。如图4所示：每次进行滤波之前，应先将循环缓冲区1中最旧的数据x(n-(N/2 -1)移到循环缓冲区2中最旧的单元x(n
12、-(N-1)，再用新来的样值x(n)冲掉循环缓冲区最旧的数据单元，并对循环缓冲区1指针AR2加1(使用循环寻址)。然后使用FIRS指令进行乘加运算。当然，在使用FIRS指令前，需要先计算一次求和，初始化A。在RPTZ重复指令和循环寻址的配合下，完成FIR滤波。在滤波算出一个输出样值后，需要对AR2和AR3进行修正，使它们都再次指向各循环缓冲区数据序列中的最旧的数据单元。以便对下一个输入样值进行滤波处理。5.2用FIRS指令编程实现FIR滤波器的程序片断：.FILT_task2 STM #N375,bk STM #-1,ar0 LD IN_data,B MVDD *AR2,*AR3+0% STL
13、 B,*AR2 ADD *AR2+0%,*AR3+0%,A RPTZB,#N375-1 FIRS *AR2+0%,*AR3+0%, Coef_Tab2 MAR *+AR2(2)% ;修正指针 MAR *AR3+% LD B,-5,A stm #19592,t MPYA b STH B,OUT_dataCoef_Tab2 .word 600 ;h(0) .word 94 .word 101 . .word 32728 .word 32767 ;h(N/2-1) .end6.结束语 本文论述了基于TMS320VC5402芯片实现FIR滤波器的技术。FIRS指令充分利用了滤波器系数的对称性，乘法次数
14、为用MAC指令时的一半，大大减少了运算量，提高了滤波效率。并且需要的滤波器系数存储器大小也只有MAC指令时的一半，节约了存储空间。同时，还获得了一个线性相位的滤波器。在实际应用时，只需改变滤波器的抽头系数，就能灵活设置FIR数字滤波器的中心频率、带宽等滤波参数。由于TMS320VC5402的指令周期为10 ns，完全能够满足实时数字信号处理的要求。实践证明，在中频数字化接收机中，TMS320VC5402配合数字下变频器用来完成基带信号的解调滤波运算，如AM解调时的直流电平恢复滤波、FM解调时的频偏滤波等，均达到了理想的数字滤波处理效果。参考文献：1 吴镇扬数字信号处理的原理与实现M南京：东南大
15、学出版社，20022 维纳.K.恩格尔,约翰.G.普罗克斯数字信号处理使用MATLABM 刘树棠译西安：西安交通大学出版社，20023 TMS320C54X DSP Referense SetTI Company,20014 汪安民TMS320C54XX DSP实用技术M北京：清华大学出版社，20025 Richard G.Lyons(美)Understanding Digital Signal Processing(Second Edition) M 北京：机械工业出版社，2005.1作者简介：薛继华 男，1976年1 月生于江苏省如皋市，1999年江苏技术师范学院本科毕业，2003年至今在
16、东南大学无线电系攻读硕士学位，研究方向为信号与信息处理。(mobile tel：（0）13584670016；E-mail：xjhnt)沈琰 女，1968年4月生于山东省东营市，1990年毕业于合肥工业大学，2003年至今在东南大学无线电系攻读硕士学位，研究方向为信号与信息处理。( tel：0546-8060073)Editors note: Judson Jones is a meteorologist, journalist and photographer. He has freelanced with CNN for four years, covering severe weathe
17、r from tornadoes to typhoons. Follow him on Twitter: jnjonesjr (CNN) - I will always wonder what it was like to huddle around a shortwave radio and through the crackling static from space hear the faint beeps of the worlds first satellite - Sputnik. I also missed watching Neil Armstrong step foot on
18、 the moon and the first space shuttle take off for the stars. Those events were way before my time.As a kid, I was fascinated with what goes on in the sky, and when NASA pulled the plug on the shuttle program I was heartbroken. Yet the privatized space race has renewed my childhood dreams to reach f
19、or the stars.As a meteorologist, Ive still seen many important weather and space events, but right now, if you were sitting next to me, youd hear my foot tapping rapidly under my desk. Im anxious for the next one: a space capsule hanging from a crane in the New Mexico desert.Its like the set for a G
20、eorge Lucas movie floating to the edge of space.You and I will have the chance to watch a man take a leap into an unimaginable free fall from the edge of space - live.The (lack of) air up there Watch man jump from 96,000 feet Tuesday, I sat at work glued to the live stream of the Red Bull Stratos Mi
21、ssion. I watched the balloons positioned at different altitudes in the sky to test the winds, knowing that if they would just line up in a vertical straight line we would be go for launch.I feel this mission was created for me because I am also a journalist and a photographer, but above all I live f
22、or taking a leap of faith - the feeling of pushing the envelope into uncharted territory.The guy who is going to do this, Felix Baumgartner, must have that same feeling, at a level I will never reach. However, it did not stop me from feeling his pain when a gust of swirling wind kicked up and twiste
23、d the partially filled balloon that would take him to the upper end of our atmosphere. As soon as the 40-acre balloon, with skin no thicker than a dry cleaning bag, scraped the ground I knew it was over.How claustrophobia almost grounded supersonic skydiverWith each twist, you could see the wrinkles
24、 of disappointment on the face of the current record holder and capcom (capsule communications), Col. Joe Kittinger. He hung his head low in mission control as he told Baumgartner the disappointing news: Mission aborted.The supersonic descent could happen as early as Sunday.The weather plays an impo
25、rtant role in this mission. Starting at the ground, conditions have to be very calm - winds less than 2 mph, with no precipitation or humidity and limited cloud cover. The balloon, with capsule attached, will move through the lower level of the atmosphere (the troposphere) where our day-to-day weath
26、er lives. It will climb higher than the tip of Mount Everest (5.5 miles/8.85 kilometers), drifting even higher than the cruising altitude of commercial airliners (5.6 miles/9.17 kilometers) and into the stratosphere. As he crosses the boundary layer (called the tropopause), he can expect a lot of tu
27、rbulence.The balloon will slowly drift to the edge of space at 120,000 feet (22.7 miles/36.53 kilometers). Here, Fearless Felix will unclip. He will roll back the door.Then, I would assume, he will slowly step out onto something resembling an Olympic diving platform.Below, the Earth becomes the conc
28、rete bottom of a swimming pool that he wants to land on, but not too hard. Still, hell be traveling fast, so despite the distance, it will not be like diving into the deep end of a pool. It will be like he is diving into the shallow end.Skydiver preps for the big jumpWhen he jumps, he is expected to
29、 reach the speed of sound - 690 mph (1,110 kph) - in less than 40 seconds. Like hitting the top of the water, he will begin to slow as he approaches the more dense air closer to Earth. But this will not be enough to stop him completely.If he goes too fast or spins out of control, he has a stabilizat
30、ion parachute that can be deployed to slow him down. His team hopes its not needed. Instead, he plans to deploy his 270-square-foot (25-square-meter) main chute at an altitude of around 5,000 feet (1,524 meters).In order to deploy this chute successfully, he will have to slow to 172 mph (277 kph). H
31、e will have a reserve parachute that will open automatically if he loses consciousness at mach speeds.Even if everything goes as planned, it wont. Baumgartner still will free fall at a speed that would cause you and me to pass out, and no parachute is guaranteed to work higher than 25,000 feet (7,62
32、0 meters).It might not be the moon, but Kittinger free fell from 102,800 feet in 1960 - at the dawn of an infamous space race that captured the hearts of many. Baumgartner will attempt to break that record, a feat that boggles the mind. This is one of those monumental moments I will always remember, because there is no way Id miss this.
