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Question for fir accelerator

Question asked by Graydon on Nov 22, 2016
Latest reply on Dec 26, 2016 by Graydon

Hello, I have two questions for using fir accelerator:

1. I downloaded a example code from FIR Accelerator for 21489 .....  and there are some piece of code like this,

Float_Out_L = circptr(Float_Out_L,1,input_left, TAPS + AUDIO_BLOCK_SIZE - 1);
Float_Out_R = circptr(Float_Out_R,1,input_right,TAPS + AUDIO_BLOCK_SIZE - 1);

Why I need to use circptr function, and I looked the datasheet which instroduced fir input data stored in the memory is:

x[n-(N-1)], x[n-(N-2)]
x[n-1], x[n], x[n+1]


As this, the WINDOWS_SIZE sample could be always put in the end of input buffer(x[n], x[n+1]....x[n+W-1]).. However, I have ever try it, the output is a mess. But I use circptr it works.


2. the second question is about the FIR delay time, I try use library function fir and measure the delay time is (N)/2 * sample interval ..  It's right .          But  I use FIR accelerator ,the delay time is unstable, is different within my every measure. I feel it is unthinkable.