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Improved documentation of all vhd modules except testbenches and lcd driver

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T-moe
2016-06-19 15:58:29 +02:00
parent 78ea176aac
commit f5f862c044
4 changed files with 163 additions and 142 deletions
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54
dds.vhd
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@@ -25,66 +25,72 @@ entity dds is
end dds;
architecture Behavioral of dds is
signal m, idx : unsigned(acc_res -1 downto 0):= (others => '0');
signal idx_phase : unsigned(phase_res-1 downto 0) := (others => '0');
signal amp_rect, amp_saw, amp_tria, amp_sin : unsigned (adc_res-1 downto 0);
signal m, idx : unsigned(acc_res -1 downto 0):= (others => '0'); -- phase jump size and accumulator (see Fundamentals of Direct Digital Synthesis for details about their function)
signal idx_phase : unsigned(phase_res-1 downto 0) := (others => '0'); -- relevant (=leftmost) bits of the phase acccumulator
signal amp_rect, amp_saw, amp_tria, amp_sin : unsigned (adc_res-1 downto 0); -- the current amplitudes of all 4 signal forms
-- Function to genenerate and store the sine wave in the rom.
-- Current code: Only store 1/4 of a sine wave and use symmetries.
-- Uncommented code: Store the entire sine wave (decrease adc_width to 8)
type storage is array (((2**phase_res)/4)-1 downto 0) of unsigned (adc_res-2 downto 0);
--type storage is array (((2**phase_res))-1 downto 0) of unsigned (adc_res-1 downto 0);
function gen_sin_wave return storage is
variable temp : storage;
begin
forLoop: for i in 0 to temp'high loop
forLoop: for i in 0 to temp'high loop -- for each element in the array
temp(i) := to_unsigned(integer(real((2**(adc_res-1))-1)*sin((real(i)*MATH_PI/2.0)/real(temp'high))),adc_res-1);
--temp(i) := to_unsigned(integer(real(2**(adc_res-1) -1) + real((2**(adc_res-1))-1)*sin((real(i)*MATH_PI*2.0)/real(temp'high))),adc_res);
--temp(i) := to_unsigned(integer(real(2**(adc_res-1) -1) + real((2**(adc_res-1))-1)*sin((real(i)*MATH_PI*2.0)/real(temp'high))),adc_res);
end loop;
return temp;
end function gen_sin_wave;
constant sin_wave : storage := gen_sin_wave;
constant sin_wave : storage := gen_sin_wave; -- rom for sin wave
begin
-- Calculate jump size according to input frequency
-- m = fout*(2^n)/fclk = fout*((2^n)*(2^k)/fclk)/(2^k) with k=ceil(log2(fclk)), n=acc_res
m <= resize( (resize(freq,64)
*
(shift_left(to_unsigned(1,64),acc_res + log2_int(clk_freq)) / clk_freq))
/to_unsigned(2**log2_int(clk_freq),64),acc_res);
-- Amplitude of the square wave
amp_rect <= to_unsigned(0,adc_res) when idx(acc_res-1)='0' else -- 0 for half of the time
to_unsigned((2**adc_res)-1,adc_res); --1 for the rest
-- Amplitude of the sawtooth wave
amp_saw <= idx(acc_res -1 downto acc_res - adc_res); -- Exactly the value of the uppermost bits of the phase acc
-- Amplitude of the triangle wave
amp_tria <= idx(acc_res -2 downto acc_res - adc_res - 1) -- The value of the uppermost bits, except the uppermost one (= double the frequency)
when idx(acc_res-1)='0' else -- during half of the time
((2**adc_res)-1)- (idx(acc_res -2 downto acc_res - adc_res - 1)); -- and the complement, the rest of the time
amp_rect <= to_unsigned(0,adc_res) when idx(acc_res-1)='0' else
to_unsigned((2**adc_res)-1,adc_res);
amp_saw <= idx(acc_res -1 downto acc_res - adc_res);
amp_tria <= idx(acc_res -2 downto acc_res - adc_res) & "0"
when idx(acc_res-1)='0' else
((2**adc_res)-1)- (idx(acc_res -2 downto acc_res - adc_res) & "0");
idx_phase <= idx(acc_res -1 downto acc_res - phase_res); -- take only the uppermost bits for the sine lookup
idx_phase <= idx(acc_res -1 downto acc_res - phase_res);
--amp_sin <= sin_wave(to_integer(idx_phase));
-- Amplitude of the sine wave
-- Code if we had stored the whole sinewave:
-- amp_sin <= sin_wave(to_integer(idx_phase));
-- Current Code (only 1/4 of the sine wave stored)
amp_sin <= to_unsigned((2**(adc_res-1)) - 1,adc_res) + sin_wave(to_integer(idx_phase(phase_res-3 downto 0))) when idx_phase(phase_res-1 downto phase_res-2)="00" else
to_unsigned((2**(adc_res-1)) - 1,adc_res) + sin_wave(to_integer(((2**(phase_res-2))-1) - idx_phase(phase_res-3 downto 0))) when idx_phase(phase_res-1 downto phase_res-2)="01" else
to_unsigned((2**(adc_res-1)) - 1,adc_res) - sin_wave(to_integer(idx_phase(phase_res-3 downto 0))) when idx_phase(phase_res-1 downto phase_res-2)="10" else
to_unsigned((2**(adc_res-1)) - 1,adc_res) - sin_wave(to_integer(((2**(phase_res-2))-1) - idx_phase(phase_res-3 downto 0)));
-- Output the selected amplitue using a multiplexer (00=Rectancle, 01=Sawtooth, 10=Triangle, 11=Sine)
amp <= to_unsigned(0,adc_res) when freq = to_unsigned(0,freq_res) else
amp_rect when form = "00" else
amp_saw when form ="01" else
amp_tria when form = "10" else
amp_sin;
-- Process for the phase accumulator (sequential)
P1: process(clk)
begin
if(rising_edge(clk)) then
idx <= (idx+m);
idx <= (idx+m); -- increment phase accumulator according to jump size. overflow is wanted.
end if;
end process P1;
end Behavioral;