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[/] [cordic/] [trunk/] [polar2rect/] [p2r_CordicPipe.vhd] - Rev 13
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-- -- file: p2r_CordicPipe.vhd -- author: Richard Herveille -- rev. 1.0 initial release library ieee; use ieee.std_logic_1164.all; use ieee.std_logic_arith.all; entity p2r_CordicPipe is generic( WIDTH : natural := 16; PIPEID : natural := 1 ); port( clk : in std_logic; ena : in std_logic; Xi : in signed(WIDTH -1 downto 0); Yi : in signed(WIDTH -1 downto 0); Zi : in signed(19 downto 0); Xo : out signed(WIDTH -1 downto 0); Yo : out signed(WIDTH -1 downto 0); Zo : out signed(19 downto 0) ); end entity p2r_CordicPipe; architecture dataflow of p2r_CordicPipe is -- -- functions -- -- Function CATAN (constante arc-tangent). -- This is a lookup table containing pre-calculated arc-tangents. -- 'n' is the number of the pipe, returned is a 20bit arc-tangent value. -- The numbers are calculated as follows: Z(n) = atan(1/2^n) -- examples: -- 20bit values => 2^20 = 2pi(rad) -- 1(rad) = 2^20/2pi = 166886.053.... -- n:0, atan(1/1) = 0.7853...(rad) -- 0.7853... * 166886.053... = 131072(dec) = 20000(hex) -- n:1, atan(1/2) = 0.4636...(rad) -- 0.4636... * 166886.053... = 77376.32(dec) = 12E40(hex) -- n:2, atan(1/4) = 0.2449...(rad) -- 0.2449... * 166886.053... = 40883.52(dec) = 9FB3(hex) -- n:3, atan(1/8) = 0.1243...(rad) -- 0.1243... * 166886.053... = 20753.11(dec) = 5111(hex) -- function CATAN(n :natural) return integer is variable result :integer; begin case n is when 0 => result := 16#020000#; when 1 => result := 16#012E40#; when 2 => result := 16#09FB4#; when 3 => result := 16#05111#; when 4 => result := 16#028B1#; when 5 => result := 16#0145D#; when 6 => result := 16#0A2F#; when 7 => result := 16#0518#; when 8 => result := 16#028C#; when 9 => result := 16#0146#; when 10 => result := 16#0A3#; when 11 => result := 16#051#; when 12 => result := 16#029#; when 13 => result := 16#014#; when 14 => result := 16#0A#; when 15 => result := 16#05#; when 16 => result := 16#03#; when 17 => result := 16#01#; when others => result := 16#0#; end case; return result; end CATAN; -- function Delta is actually an arithmatic shift right -- This strange construction is needed for compatibility with Xilinx WebPack function Delta(Arg : signed; Cnt : natural) return signed is variable tmp : signed(Arg'range); constant lo : integer := Arg'high -cnt +1; begin for n in Arg'high downto lo loop tmp(n) := Arg(Arg'high); end loop; for n in Arg'high -cnt downto 0 loop tmp(n) := Arg(n +cnt); end loop; return tmp; end function Delta; function AddSub(dataa, datab : in signed; add_sub : in std_logic) return signed is begin if (add_sub = '1') then return dataa + datab; else return dataa - datab; end if; end; -- -- ARCHITECTURE BODY -- signal dX, Xresult : signed(WIDTH -1 downto 0); signal dY, Yresult : signed(WIDTH -1 downto 0); signal atan, Zresult : signed(19 downto 0); signal Zneg, Zpos : std_logic; begin dX <= Delta(Xi, PIPEID); dY <= Delta(Yi, PIPEID); atan <= conv_signed( catan(PIPEID), 20); -- generate adder structures Zneg <= Zi(19); Zpos <= not Zi(19); -- xadd Xresult <= AddSub(Xi, dY, Zneg); -- yadd Yresult <= AddSub(Yi, dX, Zpos); -- zadd Zresult <= AddSub(Zi, atan, Zneg); gen_regs: process(clk) begin if(clk'event and clk='1') then if (ena = '1') then Xo <= Xresult; Yo <= Yresult; Zo <= Zresult; end if; end if; end process; end architecture dataflow;
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