Subversion Repositories cordic

--

-- file: r2p_CordicPipe.vhd

-- author: Richard Herveille

-- rev. 1.0 initial release

-- rev. 1.1 March 19th, 2001. Richard Herveille. Changed function Delta, it is compatible with Xilinx WebPack software now

-- rev. 1.2 May   18th, 2001. Richard Herveille. Added documentation to function ATAN (by popular request).

-- rev. 1.3 June   4th, 2001. Richard Herveille. Revised design (made it simpler and easier to understand). 

library ieee;

use ieee.std_logic_1164.all;

use ieee.std_logic_arith.all;

entity r2p_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 r2p_CordicPipe;

architecture dataflow of r2p_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: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 Yneg, Ypos       : std_logic;

begin

        dX <= Delta(Xi, PIPEID);

        dY <= Delta(Yi, PIPEID);

        atan <= conv_signed( catan(PIPEID), 20); -- Angle can not be negative, catan never returns a negative value, so conv_signed can be used

        -- generate adder structures

        Yneg <= Yi(WIDTH -1);

        Ypos <= not Yi(WIDTH -1);

        -- xadd

    Xresult <= AddSub(Xi, dY, YPos);

        -- yadd 

        Yresult <= AddSub(Yi, dX, Yneg);

        -- zadd

        Zresult <= AddSub(Zi, atan, Ypos);

        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;