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Discussion Groups | TMS320C54x | FIR Filter Implementation
Technical discussions about the TI C54x DSPs (including the c5401, c5402, c5402a, c5404, c5407, c5409, c5409a, c5410, c5410a, c5416, c5420, c5421, c5441, c549, c5470 and c5471).
FIR Filter Implementation - dspswansea - Feb 25 10:31:00 2002
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Hi Everyone, I am having some major problems trying to implement FIR filters on the TMS320C5402 as part of my University Porject. This is compounded by the fact that I am new to DSP. I am trying to implement two filters a Low-Pass (Interpolating) Filter and a Combfilter. Using Matlab I have found the filter coefficients that I require. I thought a good place to start was to use the "FIRTEST" examples that come with CCS, these are located in: ti\examples\dsk5402 \xdias\firtest. In these examples i tried to change the Filter coeffiecint in the example and see what happens ( the input is an impulse), but the output is a string of ZEROS. Even in the TEXAS example i get a String of Zeros! (when the impulse responce would be 1,2,3,4,4,3,2,1) The only time i can get output other than ZERO is when a coeffiecient is negative, and then its only ever -1. Also it appear that the output array is reversed (but I think that can rectifed simply enough). It took me a while to actually get the ouput to be displayed, but it via "DSP/BIOS ---> Message Log" I am a bit stuck now. Is there a problem with the Filtering Algorith with CCS? Has anyone else experienced this/Or is it me doing something daft (quite likely!). I would really appreciate any pointers or advice from anyone out there no matter how small. Thanks for you time MARK |
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Re: FIR Filter Implementation - Author Unknown - Feb 25 14:41:00 2002
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Hi, You'll do well to leave those examples alone. A good way to start is writing the code yourself (I hope you are familiar with fundamentals of fixed point arithmetic). A simple FIR Filter code is : /* Update the filter buffer */ for (j = LENGTH; j > 0; j--) filter_buffer[j] = filter_buffer[j-1]; filter_buffer[0] = input_sample; /* Convolve the filter_buffer with filter_coeff */ output = 0; for (j = 0; j < LENGTH; j++) output += filter_buffer[j] * filter_coeff[j]; NOTE: The update filter buffer can be done very efficiently if you keep a head and tail pointers for circular buffer. The above code will work well in case of floating point numbers. You'll need to do somethings with fixed-point numbers though. I also hope you are trying to write a C Code first. Hope it helps, Sachin "dspswansea" <> on 02/25/2002 04:01:39 PM To: cc: (bcc: Sachin Gupta/HSS) Subject: [c54x] FIR Filter Implementation Hi Everyone, I am having some major problems trying to implement FIR filters on the TMS320C5402 as part of my University Porject. This is compounded by the fact that I am new to DSP. I am trying to implement two filters a Low-Pass (Interpolating) Filter and a Combfilter. Using Matlab I have found the filter coefficients that I require. I thought a good place to start was to use the "FIRTEST" examples that come with CCS, these are located in: ti\examples\dsk5402 \xdias\firtest. In these examples i tried to change the Filter coeffiecint in the example and see what happens ( the input is an impulse), but the output is a string of ZEROS. Even in the TEXAS example i get a String of Zeros! (when the impulse responce would be 1,2,3,4,4,3,2,1) The only time i can get output other than ZERO is when a coeffiecient is negative, and then its only ever -1. Also it appear that the output array is reversed (but I think that can rectifed simply enough). It took me a while to actually get the ouput to be displayed, but it via "DSP/BIOS ---> Message Log" I am a bit stuck now. Is there a problem with the Filtering Algorith with CCS? Has anyone else experienced this/Or is it me doing something daft (quite likely!). I would really appreciate any pointers or advice from anyone out there no matter how small. Thanks for you time MARK _____________________________________ |
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