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library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;
use ieee.math_real.all;
entity cos_table is
generic (
Q : positive := 12;
INPUT_LENGTH : positive := 16;
OUTPUT_LENGTH : positive := 16;
DPHASE_STEPS_90 : positive := 4
);
port(
reset : in std_logic;
clock : in std_logic;
phase : in unsigned(INPUT_LENGTH-1 downto 0);
phase_valid : in std_logic;
y : out signed(OUTPUT_LENGTH-1 downto 0);
y_valid : out std_logic
);
end entity;
architecture arch of cos_table is
type cos_table_t is array(natural range <>) of signed(INPUT_LENGTH-1 downto 0);
function generate_cos_table(steps, qscale : positive) return cos_table_t is
variable table : cos_table_t(0 to steps + 1) := (others => (others =>'0'));
begin
for i in table'range loop
table(i) := to_signed(integer(round(real(qscale)*cos(MATH_PI/2.0 * real(real(i)/real(steps))))),table(i)'length);
end loop;
return table;
end function;
constant table : cos_table_t(0 to DPHASE_STEPS_90 +1) := generate_cos_table(DPHASE_STEPS_90, 2**Q);
begin
find_y : process(clock,reset)
variable cur_index : natural;
begin
if reset = '1' then
y <= (others=>'0');
y_valid <= '0';
elsif rising_edge(clock) then
y_valid <= '0';
if phase_valid = '1' then
y_valid <= '1';
if phase <= DPHASE_STEPS_90 then
y <= (table(to_integer(phase)));
cur_index := to_integer(phase);
elsif phase <= (2*DPHASE_STEPS_90) then
y <= -(table(DPHASE_STEPS_90 - (to_integer(phase) -(DPHASE_STEPS_90))));
cur_index := DPHASE_STEPS_90 - (to_integer(phase) -(DPHASE_STEPS_90));
elsif phase <= (3*DPHASE_STEPS_90) then
y <= -(table(to_integer(phase)- (2*DPHASE_STEPS_90)));
cur_index := to_integer(phase)- (2*DPHASE_STEPS_90);
else
y<= (table(DPHASE_STEPS_90 - (to_integer(phase)-(3*DPHASE_STEPS_90))));
cur_index := DPHASE_STEPS_90 - (to_integer(phase)-(3*DPHASE_STEPS_90));
end if;
end if;
end if;
end process;
end architecture;
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