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Implementation of FIR accelerator



		

			

									
					    MarcS.
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Nov 11, 2009 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    Hi,
    
 
    I use the SHARC 21469 and I would like to use the IIR and FIR accelerator units for processing audio data.
    
 
    I found an IIR Accelerator Talkthrough example in the forum posted by Mitesh Moonat which works fine. 
    
 

    I tried to modify it to use the FIR accelerator, but it does not work properly and I don't know why.
    
 
    Perhaps anyone has a working code example or you can take look at my code which is attached to the posting.
    
 
    Best Regards,
    
 
    Marc
    
									
			        
		
    

				
							Talkthrough_FIR_Accelerator.zip
							
        

    
    Tags: 
                                            
                 accelerator
                
                                                    
                 fir
                
                                                    
                 adsp-2146x
                
                                
            
    
    
    

		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    


	















    
	
    
	
    
					



			


				
	









	
      
	

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      •  Analog Employees  
      
            
			                            
                                                                                                                        
            
				
			
            
					
      
	
      

		
		
      
					
      Hi Marc,
      
 
      There is a number of FIR examples now shipping with VisualDSP++ 5.0 Update 7: C:\Program Files\Analog Devices\VisualDSP 5.0 (Update 7)\214xx\Examples\ADSP-21469 EZ-Board
      
 
      
 
      
 
      VisualDSP++ 5.0 Update 7 was released just last week.  The update file and release notes can be found here:
      
 http://www.analog.com/en/embedded-processing-dsp/software-and-reference-designs/content/visualdsp_tools_upgrades/fca.html
 
      
 
       
      
 
 
      
 
      
 
 
      Regards,
      
 
      MKokaly
      
 
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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        Hello Marc and MKokaly!
        
 
         
        
 
        I have more a comment than a solution.
        
 
         
        
 
        I also tried to implement the FIR-Accelerator (and the FFT Accelerator) in talk through mode, but with little success. In all examples (also the new ones  except the Talkthrough_FIR_Accelerator example) and manuals it is not shown/explained how to use the Accelerator periodically with the same coefficients.
        
 
         
        
 
        The solution for the IIR example to clear and set the DMA enable bit does not work for in the FIR and FFT case. A assume the problem is related to the DMA start and stop conditions (Processor Hardware Reference 2-37). In the FFT case it helps to (re)set the "chain pointer register address field" to wake up the Accelerator.
        
 
         
        
 
         
        
 
        My big open question is, what I have to do to bring the Accelerator from the idle mode in the processing mode again. In the manuals is only written "waits for core intervention", but I found no explanation what kind of to core intervention. For example Figure 6-5 of the hardware reference manual shows the program flow and explains everything except the last core intervention.
        
 
          
        
 
          
        
 
        Big thanks for any help.
        
 
          
        
 
          
        
 
        -Thomas
        
 
         
        
 
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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          Hi Divya,
          
 
          thank you for helping me, but in the code you attached I can't find any modifications and it doesn't work properly.
          
 
          Perhaps you have just attached the wrong code.
          
 
          Regards,
          
 
          Marc
          
			
          

		
			
	      

		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
						
				
						
				
				
		
		
          
			
		
          
	
          

          

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          Hi Marc,
          
 
          I got a chance to look at your code I modified the Talkthru code you attached for FIR filtering. The problem with the code was the input buffer handling was not right. The input buffer handling should be different when compared to that of IIR. Data must be fed to the input buffer in a circular buffer fashion to be able to perform the FIR filtering on the input buffer using the accelerators.
          
 
          Thomas,
          
 
          If you are using CAI (channel auto iterate bit ) you do not need to have any core intervention. For single iteration mode you will need to reenable the FIR accelerator for processing the next set of data. Please refer to the attached code.
          
 
          Hope this helps.
          
 
          Thanks,
          
 
          Divya
          
 
          Message was edited by: DivyaS Removed the attachment as the wrong code was attached.
          
			
          

		
			
	      

		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
						
				
						
				
				
		
		
          
			
		
          
	
          

          

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          Hi Marc,
          
 
          oops! I attached the wrong code. Here is the right one.
          
 
          Thanks,
          
 
          Divya
          
			
          

		
			
	      

		
				Talkthrough_FIR_Accelerator.zip
			
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
				
						
						
				
				
		
		
          
			
		
          
	
          

          

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            Hi Divya,
            
 
            the FIR accelerator is working fine. Thanks a lot for your help!
            
 
            I have one last question to the code: Which role plays the variable 'count' in your code?
            
 
            And just one annotation to the code: You should modify the coefficient index register in the TCBs from 'coeffs+63' to 'coeffs+TAPS-1', so it is easier to to change the length of coefficients or the audio block size.
            
 
            Best regards,
            
 
            Marc
            
			
            

		
			
	      

		
		
	
            
	
            
		
            
			
		
            
	
            
	
            
		
						
						
				
						
				
				
		
		
            
			
		
            
	
            

            

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              Hi Thomas,
              
 
              at this point you should use the version which fits better to your framwork code. As long as you are processing symmetric FIR filters it makes no difference.
              
 
              Important for me is that other users who want to work with the code regard this point.
              
 
              Regards,
              
 
              Marc
              
			
              

		
			
	      

		
		
	
              
	
              
		
              
			
		
              
	
              
	
              
		
						
						
				
						
				
				
		
		
              
			
		
              
	
              

              

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                Hi Divya,
                
 
                 
                
 
                Thanks for the nice example code. It works fine.
                
 
                With the DAM enable bit I was wrong. I had a bug in my code and therefore I was not running.
                
 
                 
                
 
                 
                
 
                Big Thanks
                
 
                Thomas
                
 
                 
                
 
                 
                
 
                To Marc: Maybe the simplest solution is the save the filter coefficients in reverse order, then you can use the address coeffs and the modifier +1.
                
 
                
			
                

		
			
	      

		
		
	
                
	
                
		
                
			
		
                
	
                
	
                
		
						
						
				
						
				
				
		
		
                
			
		
                
	
                

                

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                Hi Marc,
                
 
                Regarding your question to the count variable, I just used it for debug purposes. I used the coeffs+63 since you had the coefficient buffer length of 64 and Yes for generalization you could use coeffs+TAPS-1.
                
 
                Thanks,
                
 
                Divya
                
			
                

		
			
	      

		
		
	
                
	
                
		
                
			
		
                
	
                
	
                
		
						
						
				
						
				
				
		
		
                
			
		
                
	
                

                

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                  Hi Divya,
                  
 
                  I have a further question to your code modifications. Why are the pointers initialized to "input_left + TAPS - 1"?
                  
 
                  Here is the code snippet I refer to:
                  
 
                  float *input_leftptr = input_left + TAPS -1;
                  float *input_rightptr = input_right + TAPS -1;
                  
 
                  Best regards,
                  
 
                  Marc
                  
			
                  

		
			
	      

		
		
	
                  
	
                  
		
                  
			
		
                  
	
                  
	
                  
		
						
						
				
						
				
				
		
		
                  
			
		
                  
	
                  

                  

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