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Help! FIR Filter - MATLAB fdatool - VHDL

 
 
Emel
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      01-08-2006
Hi,

I designed a 7th order FIR filter using MATLAB fdatool and obtained the
VHDL code using the HDL Coder. I think that in the following part of
the code there is a problem (Delay pipe line is an 8 element array,
whose elements are 16 bit vectors. filter_in is a 16 bit vector):

IF reset = '1' THEN
delay_pipeline(0 TO 7) <= (OTHERS => (OTHERS => '0'));
ELSIF clk'event AND clk = '1' THEN
IF clk_enable = '1' THEN
delay_pipeline(0) <= signed(filter_in);
delay_pipeline(1 TO 7) <= delay_pipeline(0 TO 6);
END IF;
END IF;

This part simply shifts previous inputs and should be saving the new
input (filter_in) into delay_pipeline(0) (which it does). However,
after delay_pipeline(0) <= signed(filter_in);, it says delay_pipeline(1
TO 7) <= delay_pipeline(0 TO 6);. As far as I know, the statements in a
process are sequential. So, if you change delay_pipeline(0) right at
the beginning, isn't the old value of delay_pipeline(0) totally gone?
Because, afterwards delay_pipeline(0) (its new value) is assigned to
delay_pipeline(1).

I think that the order of the statements needs to be changed like:

delay_pipeline(1 TO 7) <= delay_pipeline(0 TO 6);
delay_pipeline(0) <= signed(filter_in); so that the seven previous
inputs are stored in the array elements with indices from 1 to 7 and
the new(current) input is stored in the element with index 0.

I couldn't be sure. Can anyone help me? It is very crucial to me that I
understand it correctly.

Thanks in advance...

Emel

 
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