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https://opencores.org/ocsvn/cordic/cordic/trunk
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[/] [cordic/] [trunk/] [rect2polar/] [r2p_post.vhd] - Rev 13
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-- -- post.vhd -- -- Cordic post-processing block -- -- Compensate cordic algorithm K-factor; divide Radius by 1.6467, or multiply by 0.60725. -- Approximation: Ra = Ri/2 + Ri/8 - Ri/64 - Ri/512 -- Radius = Ra - Ra/4096 = Ri * 0.60727. This is a 0.0034% error. -- Implementation: Ra = (Ri/2 + Ri/8) - (Ri/64 + Ri/512) -- Radius = Ra - Ra/4096 -- Position calculated angle in correct quadrant. -- library ieee; use ieee.std_logic_1164.all; use ieee.std_logic_arith.all; entity r2p_post is port( clk : in std_logic; ena : in std_logic; Ai : in signed(19 downto 0); Ri : in unsigned(19 downto 0); Q : in std_logic_vector(2 downto 0); Ao : out signed(19 downto 0); Ro : out unsigned(19 downto 0)); end entity r2p_post; architecture dataflow of r2p_post is begin radius: block signal RadA, RadB, RadC : unsigned(19 downto 0); begin process(clk) begin if (clk'event and clk = '1') then if (ena = '1') then RadA <= ('0' & Ri(19 downto 1)) + ("000" & Ri(19 downto 3)); RadB <= ("000000" & Ri(19 downto 6)) + ("000000000" & Ri(19 downto 9)); RadC <= RadA - RadB; Ro <= RadC - RadC(19 downto 12); end if; end if; end process; end block radius; angle: block constant const_PI2 : signed(19 downto 0) := conv_signed(16#40000#, 20); -- PI / 2 constant const_PI : signed(19 downto 0) := conv_signed(16#80000#, 20); -- PI constant const_2PI : signed(19 downto 0) := (others => '0'); -- 2PI signal dQ : std_logic_vector(2 downto 1); signal ddQ : std_logic; signal AngStep1 : signed(19 downto 0); signal AngStep2 : signed(19 downto 0); begin angle_step1: process(clk, Ai, Q) variable overflow : std_logic; variable AngA, AngB, Ang : signed(19 downto 0); begin -- check if angle is negative, if so set it to zero overflow := Ai(19); --and Ai(18); if (overflow = '1') then AngA := (others => '0'); else AngA := Ai; end if; -- step 1: Xabs and Yabs are swapped -- Calculated angle is the angle between vector and Y-axis. -- ActualAngle = PI/2 - CalculatedAngle AngB := const_PI2 - AngA; if (Q(0) = '1') then Ang := AngB; else Ang := AngA; end if; if (clk'event and clk = '1') then if (ena = '1') then AngStep1 <= Ang; dQ <= q(2 downto 1); end if; end if; end process angle_step1; angle_step2: process(clk, AngStep1, dQ) variable AngA, AngB, Ang : signed(19 downto 0); begin AngA := AngStep1; -- step 2: Xvalue is negative -- Actual angle is in the second or third quadrant -- ActualAngle = PI - CalculatedAngle AngB := const_PI - AngA; if (dQ(1) = '1') then Ang := AngB; else Ang := AngA; end if; if (clk'event and clk = '1') then if (ena = '1') then AngStep2 <= Ang; ddQ <= dQ(2); end if; end if; end process angle_step2; angle_step3: process(clk, AngStep2, ddQ) variable AngA, AngB, Ang : signed(19 downto 0); begin AngA := AngStep2; -- step 3: Yvalue is negative -- Actual angle is in the third or fourth quadrant -- ActualAngle = 2PI - CalculatedAngle AngB := const_2PI - AngA; if (ddQ = '1') then Ang := AngB; else Ang := AngA; end if; if (clk'event and clk = '1') then if (ena = '1') then Ao <= Ang; end if; end if; end process angle_step3; end block angle; end;
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