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Fix noise when rapidly turning APU DACs on and off.

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This commit is contained in:
Mark Johnson
2023-04-15 00:29:47 +01:00
parent 2fb9af272e
commit 8619d4ed1f
1 changed files with 40 additions and 15 deletions
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55
rtl/gbc_snd.vhd
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@@ -1,3 +1,8 @@
-- Notes:
-- When the output DAC of each channel is disabled, the real voltage will drift
-- to 0 V at some unknown rate. Here, it is implemented as an immediate return to "0 V".
-- If this is found to not be accurate enough, an additional timer may be added.
library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
@@ -975,11 +980,12 @@ begin
SS_Sound3_BACK( 58) <= noi_playing;
SS_Sound3_BACK(62 downto 59) <= noi_vol;
square1 : process(clk, sq1_out, sq1_vol, sq1_suppressed)
square1 : process(clk, sq1_vol, sq1_svol, sq1_envsgn, sq1_out, sq1_suppressed)
constant duty_0 : std_logic_vector(0 to 7) := "00000001";
constant duty_1 : std_logic_vector(0 to 7) := "10000001";
constant duty_2 : std_logic_vector(0 to 7) := "10000111";
constant duty_3 : std_logic_vector(0 to 7) := "01111110";
constant duty_3 : std_logic_vector(0 to 7) := "01111110";
variable sq1_dac_en : boolean;
variable sq1_fcnt : unsigned(10 downto 0);
variable sq1_phase : integer range 0 to 7;
variable sq1_len : std_logic_vector(6 downto 0);
@@ -997,10 +1003,15 @@ begin
variable acc_fcnt : unsigned(11 downto 0);
variable tmp_volume : unsigned(7 downto 0); -- used in zombie mode
begin
if sq1_out = '1' and sq1_suppressed = '0' then
sq1_wav <= sq1_vol;
sq1_dac_en := (sq1_svol & sq1_envsgn) /= "00000";
if sq1_dac_en then
if sq1_out = '1' and sq1_suppressed = '0' then
sq1_wav <= sq1_vol;
else
sq1_wav <= "0000";
end if;
else
sq1_wav <= "0000";
sq1_wav <= "0111"; -- When DAC is off, settle to ~0 V.
end if;
if rising_edge(clk) then
@@ -1287,11 +1298,12 @@ begin
end if;
end process square1;
square2 : process(clk, sq2_out, sq2_vol, sq2_suppressed)
square2 : process(clk, sq2_vol, sq2_svol, sq2_envsgn, sq2_out, sq2_suppressed)
constant duty_0 : std_logic_vector(0 to 7) := "00000001";
constant duty_1 : std_logic_vector(0 to 7) := "10000001";
constant duty_2 : std_logic_vector(0 to 7) := "10000111";
constant duty_3 : std_logic_vector(0 to 7) := "01111110";
variable sq2_dac_en : boolean;
variable sq2_fcnt : unsigned(10 downto 0);
variable sq2_phase : integer range 0 to 7;
variable sq2_len : std_logic_vector(6 downto 0);
@@ -1301,14 +1313,19 @@ begin
variable acc_fcnt : unsigned(11 downto 0);
variable tmp_volume : unsigned(7 downto 0); -- used in zombie mode
begin
sq2_dac_en := (sq2_svol & sq2_envsgn) /= "00000";
if sq2_dac_en then
if sq2_out = '1' and sq2_suppressed = '0' then
sq2_wav <= sq2_vol;
else
sq2_wav <= "0000";
end if;
else
sq2_wav <= "0111"; -- When DAC is off, settle to ~0 V.
end if;
if rising_edge(clk) then
if reset = '1' then
if rising_edge(clk) then
if reset = '1' then
sq2_playing <= SS_Sound3( 39); -- '0';
sq2_fcnt := (others => '0');
sq2_phase := 0;
@@ -1499,11 +1516,13 @@ begin
variable acc_fcnt : unsigned(11 downto 0);
variable wav_trigger_freq : std_logic_vector(10 downto 0);
begin
if wav_enable = '1' and wav_playing = '0' then
if wav_enable = '0' then
wav_wav <= "0111"; -- When DAC is off, settle to ~0 V.
elsif wav_playing = '0' then
-- DAC enabled but not playing
wav_wav <= (others => '0');
else
-- DAC disabled or playing. Outputting 0 when the DAC is disabled is not correct because the voltage should transition from the previous value to 0 volt.
-- DAC enabled and wave playing
case wav_volsh is
when "01" => wav_wav <= wav_wav_r;
when "10" => wav_wav <= '0' & wav_wav_r(3 downto 1);
@@ -1616,7 +1635,8 @@ begin
end if;
end process wave;
noise : process(clk, noi_vol)
noise : process(clk, noi_vol, noi_svol, noi_envsgn)
variable noi_dac_en : boolean;
variable noi_divisor : unsigned(10 downto 0); -- Noise frequency divisor
variable noi_period : unsigned(10 downto 0); -- Noise period (calculated)
variable noi_fcnt : unsigned(10 downto 0);
@@ -1629,10 +1649,15 @@ begin
variable tmp_volume : unsigned(7 downto 0); -- used in zombie mode
variable acc_fcnt : unsigned(11 downto 0);
begin
if noi_out = '1' then
noi_wav <= noi_vol;
else
noi_wav <= "0000";
noi_dac_en := (noi_svol & noi_envsgn) /= "00000";
if noi_dac_en then
if noi_out = '1' then
noi_wav <= noi_vol;
else
noi_wav <= "0000";
end if;
else
noi_wav <= "0111"; -- When DAC is off, settle to ~0 V.
end if;
-- Sound processing