post_20b15i.vhd

一个很不错的cordic利用流水线计算正余弦的程序

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--  File: post.vhd                                       --
--  created : July 09,2001 15:00                         --
--  mail to [e-mail]                          --
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library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.STD_LOGIC_ARITH.all;
use IEEE.STD_LOGIC_SIGNED.all;

entity post_20b15i is
	port (
		clk           : in  STD_LOGIC;
		scaled_radius : in  STD_LOGIC_VECTOR (19 downto 0);
		input_angle   : in  STD_LOGIC_VECTOR (18 downto 0);
		angle         : out STD_LOGIC_VECTOR (19 downto 0);
		octant        : in  STD_LOGIC_VECTOR (2 downto 0);
		radius        : out STD_LOGIC_VECTOR (19 downto 0)
		);
end post_20b15i;

architecture post_20b15i of post_20b15i is
	
signal tmp1,tmp2,tmp3,tmp4 : std_logic_vector (20 downto 0);   
signal in_angl,ang3        : std_logic_vector (19 downto 0);
signal ang2,ang1           : std_logic_vector (18 downto 0);       
signal o0,o1               : std_logic_vector (2 downto 0);		
signal ang                 : std_logic_vector (19 downto 0); 

begin
	
	process(clk)
		variable ang : std_logic_vector (19 downto 0); 
		variable pi2 : std_logic_vector (19 downto 0); 
		variable pi  : std_logic_vector (19 downto 0); 
		variable acc : std_logic_vector (20 downto 0);         
		variable add : std_logic_vector (20 downto 0);         
		
	begin 
		if clk'event and clk='1' then  
			o0   <= octant;
			o1   <= o0;			
			ang1 <= input_angle;
			ang2 <= ang1;
			
		        ang  := o1(2) & o1(1) & "000000000000000000";


		        if o1(0) = '0' then
		           angle <= ang + sxt(ang2, 20);
		        else
		           angle <= ang - sxt(ang2, 20);
		        end if;   		           


-- approximation of 0,858785337
-- 1-((1/8+1/64)+(1/8+1/64)/256+(1/8+1/64)/4096)=0,858791351
-- this is an 0,0000060147 error	 
			
			acc    := (scaled_radius & '0');
			add    := "000" & scaled_radius(19 downto 2);
			tmp1   <= add+("000000" & scaled_radius(19 downto 5));
			tmp2   <= acc;
			tmp3   <= tmp1+("00000000" & tmp1(20 downto 8));
			tmp4   <= tmp2-("000000000000" & tmp1(20 downto 12));
			acc    := tmp4-tmp3;
			radius <= acc(20 downto 1);
		end if;
	end process;
	
end post_20b15i;