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Gehstock.Mist_FPGA/Computer_MiST/Commodore - MAX_MiST/rtl/sid_voice.vhd
Gehstock b4920d3288 1
2018-10-27 14:54:23 +02:00

657 lines
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VHDL
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-------------------------------------------------------------------------------
--
-- SID 6581 (voice)
--
-- This piece of VHDL code describes a single SID voice (sound channel)
--
-------------------------------------------------------------------------------
-- to do: - better resolution of result signal voice, this is now only 12bits
-- but it could be 20 !! Problem, it does not fit the PWM-dac
-------------------------------------------------------------------------------
library IEEE;
use IEEE.std_logic_1164.all;
--use IEEE.std_logic_arith.all;
use IEEE.std_logic_unsigned.all;
use IEEE.numeric_std.all;
-------------------------------------------------------------------------------
entity sid_voice is
port (
clk_1MHz : in std_logic; -- this line drives the oscilator
reset : in std_logic; -- active high signal (i.e. registers are reset when reset=1)
Freq_lo : in std_logic_vector(7 downto 0); -- low-byte of frequency register
Freq_hi : in std_logic_vector(7 downto 0); -- high-byte of frequency register
Pw_lo : in std_logic_vector(7 downto 0); -- low-byte of PuleWidth register
Pw_hi : in std_logic_vector(3 downto 0); -- high-nibble of PuleWidth register
Control : in std_logic_vector(7 downto 0); -- control register
Att_dec : in std_logic_vector(7 downto 0); -- attack-deccay register
Sus_Rel : in std_logic_vector(7 downto 0); -- sustain-release register
PA_MSB_in : in std_logic; -- Phase Accumulator MSB input
PA_MSB_out : out std_logic; -- Phase Accumulator MSB output
Osc : out std_logic_vector(7 downto 0); -- Voice waveform register
Env : out std_logic_vector(7 downto 0); -- Voice envelope register
voice : out std_logic_vector(11 downto 0) -- Voice waveform, this is the actual audio signal
);
end sid_voice;
architecture Behavioral of sid_voice is
-------------------------------------------------------------------------------
-- Altera multiplier
-- COMPONENT lpm_mult
-- GENERIC
-- (
-- lpm_hint : STRING;
-- lpm_representation : STRING;
-- lpm_type : STRING;
-- lpm_widtha : NATURAL;
-- lpm_widthb : NATURAL;
-- lpm_widthp : NATURAL;
-- lpm_widths : NATURAL
-- );
-- PORT
-- (
-- dataa : IN STD_LOGIC_VECTOR (11 DOWNTO 0);
-- datab : IN STD_LOGIC_VECTOR (7 DOWNTO 0);
-- result : OUT STD_LOGIC_VECTOR (19 DOWNTO 0)
-- );
-- END COMPONENT;
-------------------------------------------------------------------------------
signal accumulator : std_logic_vector(23 downto 0) := (others => '0');
signal accu_bit_prev : std_logic := '0';
signal PA_MSB_in_prev : std_logic := '0';
-- this type of signal has only two states 0 or 1 (so no more bits are required)
signal pulse : std_logic := '0';
signal sawtooth : std_logic_vector(11 downto 0) := (others => '0');
signal triangle : std_logic_vector(11 downto 0) := (others => '0');
signal noise : std_logic_vector(11 downto 0) := (others => '0');
signal LFSR : std_logic_vector(22 downto 0) := (others => '0');
signal frequency : std_logic_vector(15 downto 0) := (others => '0');
signal pulsewidth : std_logic_vector(11 downto 0) := (others => '0');
-- Envelope Generator
type envelope_state_types is (idle, attack, attack_lp, decay, decay_lp, sustain, releases, release_lp);
signal cur_state, next_state : envelope_state_types;
signal divider_value : integer range 0 to 2**15 - 1 :=0;
signal divider_attack : integer range 0 to 2**15 - 1 :=0;
signal divider_dec_rel : integer range 0 to 2**15 - 1 :=0;
signal divider_counter : integer range 0 to 2**18 - 1 :=0;
signal exp_table_value : integer range 0 to 2**18 - 1 :=0;
signal exp_table_active : std_logic := '0';
signal divider_rst : std_logic := '0';
signal Dec_rel : std_logic_vector(3 downto 0) := (others => '0');
signal Dec_rel_sel : std_logic := '0';
signal env_counter : std_logic_vector(17 downto 0) := (others => '0');
signal env_count_hold_A : std_logic := '0';
signal env_count_hold_B : std_logic := '0';
signal env_cnt_up : std_logic := '0';
signal env_cnt_clear : std_logic := '0';
signal signal_mux : std_logic_vector(17 downto 0) := (others => '0');
signal signal_vol : std_logic_vector(35 downto 0) := (others => '0');
-------------------------------------------------------------------------------------
-- stop the oscillator when test = '1'
alias test : std_logic is Control(3);
-- Ring Modulation was accomplished by substituting the accumulator MSB of an
-- oscillator in the EXOR function of the triangle waveform generator with the
-- accumulator MSB of the previous oscillator. That is why the triangle waveform
-- must be selected to use Ring Modulation.
alias ringmod : std_logic is Control(2);
-- Hard Sync was accomplished by clearing the accumulator of an Oscillator
-- based on the accumulator MSB of the previous oscillator.
alias sync : std_logic is Control(1);
--
alias gate : std_logic is Control(0);
-------------------------------------------------------------------------------------
begin
-- output the Phase accumulator's MSB for sync and ringmod purposes
PA_MSB_out <= accumulator(23);
-- output the upper 8-bits of the waveform.
-- Useful for random numbers (noise must be selected)
Osc <= signal_mux(11 downto 4);
-- output the envelope register, for special sound effects when connecting this
-- signal to the input of other channels/voices
Env <= env_counter(7 downto 0);
-- use the register value to fill the variable
frequency(15 downto 8) <= Freq_hi(7 downto 0);
--
frequency(7 downto 0) <= Freq_lo(7 downto 0);
-- use the register value to fill the variable
pulsewidth(11 downto 8) <= Pw_hi(3 downto 0);
--
pulsewidth(7 downto 0) <= Pw_lo(7 downto 0);
--
voice <= signal_vol(19 downto 8);
-- Phase accumulator :
-- "As I recall, the Oscillator is a 24-bit phase-accumulating design of which
-- the lower 16-bits are programmable for pitch control. The output of the
-- accumulator goes directly to a D/A converter through a waveform selector.
-- Normally, the output of a phase-accumulating oscillator would be used as an
-- address into memory which contained a wavetable, but SID had to be entirely
-- self-contained and there was no room at all for a wavetable on the chip."
-- "Hard Sync was accomplished by clearing the accumulator of an Oscillator
-- based on the accumulator MSB of the previous oscillator."
PhaseAcc:process(clk_1MHz)
begin
if (rising_edge(clk_1MHz)) then
PA_MSB_in_prev <= PA_MSB_in;
-- the reset and test signal can stop the oscillator,
-- stopping the oscillator is very useful when you want to play "samples"
if ((reset = '1') or (test = '1') or ((sync = '1') and (PA_MSB_in_prev /= PA_MSB_in) and (PA_MSB_in = '0'))) then
accumulator <= (others => '0');
else
-- accumulate the new phase (i.o.w. increment env_counter with the freq. value)
accumulator <= accumulator + ("0" & frequency(15 downto 0));
end if;
end if;
end process;
-- Sawtooth waveform :
-- "The Sawtooth waveform was created by sending the upper 12-bits of the
-- accumulator to the 12-bit Waveform D/A."
Snd_Sawtooth:process(clk_1MHz)
begin
if (rising_edge(clk_1MHz)) then
sawtooth <= accumulator(23 downto 12);
end if;
end process;
--Pulse waveform :
-- "The Pulse waveform was created by sending the upper 12-bits of the
-- accumulator to a 12-bit digital comparator. The output of the comparator was
-- either a one or a zero. This single output was then sent to all 12 bits of
-- the Waveform D/A. "
Snd_pulse:process(clk_1MHz)
begin
if (rising_edge(clk_1MHz)) then
if ((accumulator(23 downto 12)) >= (pulsewidth(11 downto 0))) then
pulse <= '1';
else
pulse <= '0';
end if;
end if;
end process;
--Triangle waveform :
-- "The Triangle waveform was created by using the MSB of the accumulator to
-- invert the remaining upper 11 accumulator bits using EXOR gates. These 11
-- bits were then left-shifted (throwing away the MSB) and sent to the Waveform
-- D/A (so the resolution of the triangle waveform was half that of the sawtooth,
-- but the amplitude and frequency were the same). "
-- "Ring Modulation was accomplished by substituting the accumulator MSB of an
-- oscillator in the EXOR function of the triangle waveform generator with the
-- accumulator MSB of the previous oscillator. That is why the triangle waveform
-- must be selected to use Ring Modulation."
Snd_triangle:process(clk_1MHz)
begin
if (rising_edge(clk_1MHz)) then
if ringmod = '0' then
-- no ringmodulation
triangle(11)<= accumulator(23) xor accumulator(22);
triangle(10)<= accumulator(23) xor accumulator(21);
triangle(9) <= accumulator(23) xor accumulator(20);
triangle(8) <= accumulator(23) xor accumulator(19);
triangle(7) <= accumulator(23) xor accumulator(18);
triangle(6) <= accumulator(23) xor accumulator(17);
triangle(5) <= accumulator(23) xor accumulator(16);
triangle(4) <= accumulator(23) xor accumulator(15);
triangle(3) <= accumulator(23) xor accumulator(14);
triangle(2) <= accumulator(23) xor accumulator(13);
triangle(1) <= accumulator(23) xor accumulator(12);
triangle(0) <= accumulator(23) xor accumulator(11);
else
-- ringmodulation by the other voice (previous voice)
triangle(11)<= PA_MSB_in xor accumulator(22);
triangle(10)<= PA_MSB_in xor accumulator(21);
triangle(9) <= PA_MSB_in xor accumulator(20);
triangle(8) <= PA_MSB_in xor accumulator(19);
triangle(7) <= PA_MSB_in xor accumulator(18);
triangle(6) <= PA_MSB_in xor accumulator(17);
triangle(5) <= PA_MSB_in xor accumulator(16);
triangle(4) <= PA_MSB_in xor accumulator(15);
triangle(3) <= PA_MSB_in xor accumulator(14);
triangle(2) <= PA_MSB_in xor accumulator(13);
triangle(1) <= PA_MSB_in xor accumulator(12);
triangle(0) <= PA_MSB_in xor accumulator(11);
end if;
end if;
end process;
--Noise (23-bit Linear Feedback Shift Register, max combinations = 8388607) :
-- "The Noise waveform was created using a 23-bit pseudo-random sequence
-- generator (i.e., a shift register with specific outputs fed back to the input
-- through combinatorial logic). The shift register was clocked by one of the
-- intermediate bits of the accumulator to keep the frequency content of the
-- noise waveform relatively the same as the pitched waveforms.
-- The upper 12-bits of the shift register were sent to the Waveform D/A."
noise <= LFSR(22 downto 11);
Snd_noise:process(clk_1MHz)
begin
if (rising_edge(clk_1MHz)) then
-- the test signal can stop the oscillator,
-- stopping the oscillator is very useful when you want to play "samples"
if ((reset = '1') or (test = '1')) then
accu_bit_prev <= '0';
-- the "seed" value (the value that eventually determines the output
-- pattern) may never be '0' otherwise the generator "locks up"
LFSR <= "00000000000000000000001";
else
accu_bit_prev <= accumulator(22);
-- when not equal to ...
if (accu_bit_prev /= accumulator(22)) then
LFSR(22 downto 1) <= LFSR(21 downto 0);
LFSR(0) <= LFSR(17) xor LFSR(22); -- see Xilinx XAPP052 for maximal LFSR taps
else
LFSR <= LFSR;
end if;
end if;
end if;
end process;
-- Waveform Output selector (MUX):
-- "Since all of the waveforms were just digital bits, the Waveform Selector
-- consisted of multiplexers that selected which waveform bits would be sent
-- to the Waveform D/A. The multiplexers were single transistors and did not
-- provide a "lock-out", allowing combinations of the waveforms to be selected.
-- The combination was actually a logical ANDing of the bits of each waveform,
-- which produced unpredictable results, so I didn't encourage this, especially
-- since it could lock up the pseudo-random sequence generator by filling it
-- with zeroes."
Snd_select:process(clk_1MHz)
begin
if (rising_edge(clk_1MHz)) then
signal_mux(11) <= (triangle(11) and Control(4)) or (sawtooth(11) and Control(5)) or (pulse and Control(6)) or (noise(11) and Control(7));
signal_mux(10) <= (triangle(10) and Control(4)) or (sawtooth(10) and Control(5)) or (pulse and Control(6)) or (noise(10) and Control(7));
signal_mux(9) <= (triangle(9) and Control(4)) or (sawtooth(9) and Control(5)) or (pulse and Control(6)) or (noise(9) and Control(7));
signal_mux(8) <= (triangle(8) and Control(4)) or (sawtooth(8) and Control(5)) or (pulse and Control(6)) or (noise(8) and Control(7));
signal_mux(7) <= (triangle(7) and Control(4)) or (sawtooth(7) and Control(5)) or (pulse and Control(6)) or (noise(7) and Control(7));
signal_mux(6) <= (triangle(6) and Control(4)) or (sawtooth(6) and Control(5)) or (pulse and Control(6)) or (noise(6) and Control(7));
signal_mux(5) <= (triangle(5) and Control(4)) or (sawtooth(5) and Control(5)) or (pulse and Control(6)) or (noise(5) and Control(7));
signal_mux(4) <= (triangle(4) and Control(4)) or (sawtooth(4) and Control(5)) or (pulse and Control(6)) or (noise(4) and Control(7));
signal_mux(3) <= (triangle(3) and Control(4)) or (sawtooth(3) and Control(5)) or (pulse and Control(6)) or (noise(3) and Control(7));
signal_mux(2) <= (triangle(2) and Control(4)) or (sawtooth(2) and Control(5)) or (pulse and Control(6)) or (noise(2) and Control(7));
signal_mux(1) <= (triangle(1) and Control(4)) or (sawtooth(1) and Control(5)) or (pulse and Control(6)) or (noise(1) and Control(7));
signal_mux(0) <= (triangle(0) and Control(4)) or (sawtooth(0) and Control(5)) or (pulse and Control(6)) or (noise(0) and Control(7));
end if;
end process;
-- Waveform envelope (volume) control :
-- "The output of the Waveform D/A (which was an analog voltage at this point)
-- was fed into the reference input of an 8-bit multiplying D/A, creating a DCA
-- (digitally-controlled-amplifier). The digital control word which modulated
-- the amplitude of the waveform came from the Envelope Generator."
-- "The 8-bit output of the Envelope Generator was then sent to the Multiplying
-- D/A converter to modulate the amplitude of the selected Oscillator Waveform
-- (to be technically accurate, actually the waveform was modulating the output
-- of the Envelope Generator, but the result is the same)."
Envelope_multiplier:process(clk_1MHz)
begin
if (rising_edge(clk_1MHz)) then
--calculate the resulting volume (due to the envelope generator) of the
--voice, signal_mux(12bit) * env_counter(8bit), so the result will
--require 20 bits !!
signal_vol <= signal_mux * env_counter;
end if;
end process;
-- Altera multiplier
-- lpm_mult_component : lpm_mult
-- GENERIC MAP
-- (
-- lpm_hint => "MAXIMIZE_SPEED=5",
-- lpm_representation => "UNSIGNED",
-- lpm_type => "LPM_MULT",
-- lpm_widtha => 12,
-- lpm_widthb => 8,
-- lpm_widthp => 20,
-- lpm_widths => 1
-- )
-- PORT MAP
-- (
-- dataa(11 downto 0) => signal_mux,
-- datab(7 downto 0) => env_counter,
-- result => signal_vol
-- );
-- Envelope generator :
-- "The Envelope Generator was simply an 8-bit up/down counter which, when
-- triggered by the Gate bit, counted from 0 to 255 at the Attack rate, from
-- 255 down to the programmed Sustain value at the Decay rate, remained at the
-- Sustain value until the Gate bit was cleared then counted down from the
-- Sustain value to 0 at the Release rate."
--
-- /\
-- / \
-- / | \________
-- / | | \
-- / | | |\
-- / | | | \
-- attack|dec|sustain|rel
-- this process controls the state machine "current-state"-value
Envelope_SM_advance: process (reset, clk_1MHz)
begin
if (reset = '1') then
cur_state <= idle;
else
if (rising_edge(clk_1MHz)) then
cur_state <= next_state;
end if;
end if;
end process;
-- this process controls the envelope (in other words, the volume control)
Envelope_SM: process (reset, cur_state, gate, divider_attack, divider_dec_rel, Att_dec, Sus_Rel, env_counter)
begin
if (reset = '1') then
next_state <= idle;
env_cnt_clear <='1';
env_cnt_up <='1';
env_count_hold_B <='1';
divider_rst <='1';
divider_value <= 0;
exp_table_active <='0';
Dec_rel_sel <='0'; -- select decay as input for decay/release table
else
env_cnt_clear <='0'; -- use this statement unless stated otherwise
env_cnt_up <='1'; -- use this statement unless stated otherwise
env_count_hold_B <='1'; -- use this statement unless stated otherwise
divider_rst <='0'; -- use this statement unless stated otherwise
divider_value <= 0; -- use this statement unless stated otherwise
exp_table_active <='0'; -- use this statement unless stated otherwise
case cur_state is
-- IDLE
when idle =>
env_cnt_clear <= '1'; -- clear envelope env_counter
divider_rst <= '1';
Dec_rel_sel <= '0'; -- select decay as input for decay/release table
if gate = '1' then
next_state <= attack;
else
next_state <= idle;
end if;
when attack =>
env_cnt_clear <= '1'; -- clear envelope env_counter
divider_rst <= '1';
divider_value <= divider_attack;
next_state <= attack_lp;
Dec_rel_sel <= '0'; -- select decay as input for decay/release table
when attack_lp =>
env_count_hold_B <= '0'; -- enable envelope env_counter
env_cnt_up <= '1'; -- envelope env_counter must count up (increment)
divider_value <= divider_attack;
Dec_rel_sel <= '0'; -- select decay as input for decay/release table
if env_counter = "11111111" then
next_state <= decay;
else
if gate = '0' then
next_state <= releases;
else
next_state <= attack_lp;
end if;
end if;
when decay =>
divider_rst <= '1';
exp_table_active <= '1'; -- activate exponential look-up table
env_cnt_up <= '0'; -- envelope env_counter must count down (decrement)
divider_value <= divider_dec_rel;
next_state <= decay_lp;
Dec_rel_sel <= '0'; -- select decay as input for decay/release table
when decay_lp =>
exp_table_active <= '1'; -- activate exponential look-up table
env_count_hold_B <= '0'; -- enable envelope env_counter
env_cnt_up <= '0'; -- envelope env_counter must count down (decrement)
divider_value <= divider_dec_rel;
Dec_rel_sel <= '0'; -- select decay as input for decay/release table
if (env_counter(7 downto 4) = Sus_Rel(7 downto 4)) then
next_state <= sustain;
else
if gate = '0' then
next_state <= releases;
else
next_state <= decay_lp;
end if;
end if;
-- "A digital comparator was used for the Sustain function. The upper
-- four bits of the Up/Down counter were compared to the programmed
-- Sustain value and would stop the clock to the Envelope Generator when
-- the counter counted down to the Sustain value. This created 16 linearly
-- spaced sustain levels without havingto go through a look-up table
-- translation between the 4-bit register value and the 8-bit Envelope
-- Generator output. It also meant that sustain levels were adjustable
-- in steps of 16. Again, more register bits would have provided higher
-- resolution."
-- "When the Gate bit was cleared, the clock would again be enabled,
-- allowing the counter to count down to zero. Like an analog envelope
-- generator, the SID Envelope Generator would track the Sustain level
-- if it was changed to a lower value during the Sustain portion of the
-- envelope, however, it would not count UP if the Sustain level were set
-- higher." Instead it would count down to '0'.
when sustain =>
divider_value <= 0;
Dec_rel_sel <='1'; -- select release as input for decay/release table
if gate = '0' then
next_state <= releases;
else
if (env_counter(7 downto 4) = Sus_Rel(7 downto 4)) then
next_state <= sustain;
else
next_state <= decay;
end if;
end if;
when releases =>
divider_rst <= '1';
exp_table_active <= '1'; -- activate exponential look-up table
env_cnt_up <= '0'; -- envelope env_counter must count down (decrement)
divider_value <= divider_dec_rel;
Dec_rel_sel <= '1'; -- select release as input for decay/release table
next_state <= release_lp;
when release_lp =>
exp_table_active <= '1'; -- activate exponential look-up table
env_count_hold_B <= '0'; -- enable envelope env_counter
env_cnt_up <= '0'; -- envelope env_counter must count down (decrement)
divider_value <= divider_dec_rel;
Dec_rel_sel <= '1'; -- select release as input for decay/release table
if env_counter = "00000000" then
next_state <= idle;
else
if gate = '1' then
next_state <= idle;
else
next_state <= release_lp;
end if;
end if;
when others =>
divider_value <= 0;
Dec_rel_sel <= '0'; -- select decay as input for decay/release table
next_state <= idle;
end case;
end if;
end process;
-- 8 bit up/down env_counter
Envelope_counter:process(clk_1MHz)
begin
if (rising_edge(clk_1MHz)) then
if ((reset = '1') or (env_cnt_clear = '1')) then
env_counter <= (others => '0');
else
if ((env_count_hold_A = '1') or (env_count_hold_B = '1'))then
env_counter <= env_counter;
else
if (env_cnt_up = '1') then
env_counter <= env_counter + 1;
else
env_counter <= env_counter - 1;
end if;
end if;
end if;
end if;
end process;
-- Divider :
-- "A programmable frequency divider was used to set the various rates
-- (unfortunately I don't remember how many bits the divider was, either 12
-- or 16 bits). A small look-up table translated the 16 register-programmable
-- values to the appropriate number to load into the frequency divider.
-- Depending on what state the Envelope Generator was in (i.e. ADS or R), the
-- appropriate register would be selected and that number would be translated
-- and loaded into the divider. Obviously it would have been better to have
-- individual bit control of the divider which would have provided great
-- resolution for each rate, however I did not have enough silicon area for a
-- lot of register bits. Using this approach, I was able to cram a wide range
-- of rates into 4 bits, allowing the ADSR to be defined in two bytes instead
-- of eight. The actual numbers in the look-up table were arrived at
-- subjectively by setting up typical patches on a Sequential Circuits Pro-1
-- and measuring the envelope times by ear (which is why the available rates
-- seem strange)!"
prog_freq_div:process(clk_1MHz)
begin
if (rising_edge(clk_1MHz)) then
if ((reset = '1') or (divider_rst = '1')) then
env_count_hold_A <= '1';
divider_counter <= 0;
else
if (divider_counter = 0) then
env_count_hold_A <= '0';
if (exp_table_active = '1') then
divider_counter <= exp_table_value;
else
divider_counter <= divider_value;
end if;
else
env_count_hold_A <= '1';
divider_counter <= divider_counter - 1;
end if;
end if;
end if;
end process;
-- Piese-wise linear approximation of an exponential :
-- "In order to more closely model the exponential decay of sounds, another
-- look-up table on the output of the Envelope Generator would sequentially
-- divide the clock to the Envelope Generator by two at specific counts in the
-- Decay and Release cycles. This created a piece-wise linear approximation of
-- an exponential. I was particularly happy how well this worked considering
-- the simplicity of the circuitry. The Attack, however, was linear, but this
-- sounded fine."
-- The clock is divided by two at specifiek values of the envelope generator to
-- create an exponential.
Exponential_table:process(clk_1MHz)
BEGIN
if (rising_edge(clk_1MHz)) then
if (reset = '1') then
exp_table_value <= 0;
else
case CONV_INTEGER(env_counter) is
when 0 to 51 => exp_table_value <= divider_value * 16;
when 52 to 101 => exp_table_value <= divider_value * 8;
when 102 to 152 => exp_table_value <= divider_value * 4;
when 153 to 203 => exp_table_value <= divider_value * 2;
when 204 to 255 => exp_table_value <= divider_value;
when others => exp_table_value <= divider_value;
end case;
end if;
end if;
end process;
-- Attack Lookup table :
-- It takes 255 clock cycles from zero to peak value. Therefore the divider
-- equals (attack rate / clockcycletime of 1MHz clock) / 254;
Attack_table:process(clk_1MHz)
begin
if (rising_edge(clk_1MHz)) then
if (reset = '1') then
divider_attack <= 0;
else
case Att_dec(7 downto 4) is
when "0000" => divider_attack <= 8; --attack rate: ( 2mS / 1uS per clockcycle) /254 steps
when "0001" => divider_attack <= 31; --attack rate: ( 8mS / 1uS per clockcycle) /254 steps
when "0010" => divider_attack <= 63; --attack rate: ( 16mS / 1uS per clockcycle) /254 steps
when "0011" => divider_attack <= 94; --attack rate: ( 24mS / 1uS per clockcycle) /254 steps
when "0100" => divider_attack <= 150; --attack rate: ( 38mS / 1uS per clockcycle) /254 steps
when "0101" => divider_attack <= 220; --attack rate: ( 56mS / 1uS per clockcycle) /254 steps
when "0110" => divider_attack <= 268; --attack rate: ( 68mS / 1uS per clockcycle) /254 steps
when "0111" => divider_attack <= 315; --attack rate: ( 80mS / 1uS per clockcycle) /254 steps
when "1000" => divider_attack <= 394; --attack rate: ( 100mS / 1uS per clockcycle) /254 steps
when "1001" => divider_attack <= 984; --attack rate: ( 250mS / 1uS per clockcycle) /254 steps
when "1010" => divider_attack <= 1968; --attack rate: ( 500mS / 1uS per clockcycle) /254 steps
when "1011" => divider_attack <= 3150; --attack rate: ( 800mS / 1uS per clockcycle) /254 steps
when "1100" => divider_attack <= 3937; --attack rate: (1000mS / 1uS per clockcycle) /254 steps
when "1101" => divider_attack <= 11811; --attack rate: (3000mS / 1uS per clockcycle) /254 steps
when "1110" => divider_attack <= 19685; --attack rate: (5000mS / 1uS per clockcycle) /254 steps
when "1111" => divider_attack <= 31496; --attack rate: (8000mS / 1uS per clockcycle) /254 steps
when others => divider_attack <= 0; --
end case;
end if;
end if;
end process;
Decay_Release_input_select:process(Dec_rel_sel, Att_dec, Sus_Rel)
begin
if (Dec_rel_sel = '0') then
Dec_rel(3 downto 0) <= Att_dec(3 downto 0);
else
Dec_rel(3 downto 0) <= Sus_rel(3 downto 0);
end if;
end process;
-- Decay Lookup table :
-- It takes 32 * 51 = 1632 clock cycles to fall from peak level to zero.
-- Release Lookup table :
-- It takes 32 * 51 = 1632 clock cycles to fall from peak level to zero.
Decay_Release_table:process(clk_1MHz)
begin
if (rising_edge(clk_1MHz)) then
if reset = '1' then
divider_dec_rel <= 0;
else
case Dec_rel(3 downto 0) is
when "0000" => divider_dec_rel <= 3; --release rate: ( 6mS / 1uS per clockcycle) / 1632
when "0001" => divider_dec_rel <= 15; --release rate: ( 24mS / 1uS per clockcycle) / 1632
when "0010" => divider_dec_rel <= 29; --release rate: ( 48mS / 1uS per clockcycle) / 1632
when "0011" => divider_dec_rel <= 44; --release rate: ( 72mS / 1uS per clockcycle) / 1632
when "0100" => divider_dec_rel <= 70; --release rate: ( 114mS / 1uS per clockcycle) / 1632
when "0101" => divider_dec_rel <= 103; --release rate: ( 168mS / 1uS per clockcycle) / 1632
when "0110" => divider_dec_rel <= 125; --release rate: ( 204mS / 1uS per clockcycle) / 1632
when "0111" => divider_dec_rel <= 147; --release rate: ( 240mS / 1uS per clockcycle) / 1632
when "1000" => divider_dec_rel <= 184; --release rate: ( 300mS / 1uS per clockcycle) / 1632
when "1001" => divider_dec_rel <= 459; --release rate: ( 750mS / 1uS per clockcycle) / 1632
when "1010" => divider_dec_rel <= 919; --release rate: ( 1500mS / 1uS per clockcycle) / 1632
when "1011" => divider_dec_rel <= 1471; --release rate: ( 2400mS / 1uS per clockcycle) / 1632
when "1100" => divider_dec_rel <= 1838; --release rate: ( 3000mS / 1uS per clockcycle) / 1632
when "1101" => divider_dec_rel <= 5515; --release rate: ( 9000mS / 1uS per clockcycle) / 1632
when "1110" => divider_dec_rel <= 9191; --release rate: (15000mS / 1uS per clockcycle) / 1632
when "1111" => divider_dec_rel <= 14706; --release rate: (24000mS / 1uS per clockcycle) / 1632
when others => divider_dec_rel <= 0; --
end case;
end if;
end if;
end process;
end Behavioral;
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