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TZXPlayer: more correct pulse level switchings
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@gyurco
gyurco committed Jan 12, 2021
1 parent 7bfd6c1 commit 19ba5fc
Showing 1 changed file with 40 additions and 20 deletions.
60 changes: 40 additions & 20 deletions tzxplayer.vhd
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Original file line number Diff line number Diff line change
Expand Up @@ -9,7 +9,6 @@ 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 tzxplayer is
generic (
Expand All @@ -27,9 +26,8 @@ port(
loop_next : out std_logic; -- active for one clock at the next iteration
stop : out std_logic; -- tape should be stopped
stop48k : out std_logic; -- tape should be stopped in 48k mode

cass_read : buffer std_logic; -- tape read signal
cass_motor : in std_logic -- 1 = tape motor is powered
cass_read : out std_logic; -- tape read signal
cass_motor : in std_logic -- 1 = tape motor is powered
);
end tzxplayer;

Expand All @@ -49,12 +47,13 @@ constant NORMAL_SYNC1_LEN : integer := 855;
constant NORMAL_SYNC2_LEN : integer := 855;
constant NORMAL_ZERO_LEN : integer := 855;
constant NORMAL_ONE_LEN : integer := 1710;
constant NORMAL_PILOT_PULSES : integer := 4096;
constant NORMAL_PILOT_PULSES : integer := 4095;

signal tap_fifo_do : std_logic_vector(7 downto 0);
signal tick_cnt : std_logic_vector(16 downto 0);
signal wave_cnt : std_logic_vector(15 downto 0);
signal wave_period : std_logic;
signal wave_inverted : std_logic;
signal skip_bytes : std_logic;
signal playing : std_logic; -- 1 = tap or wav file is playing
signal bit_cnt : std_logic_vector(2 downto 0);
Expand Down Expand Up @@ -111,6 +110,7 @@ signal data_len_dword : std_logic_vector(31 downto 0);

begin

cass_read <= wave_period;
tap_fifo_do <= host_tap_in;
process(clk)
begin
Expand All @@ -127,6 +127,7 @@ begin
loop_start <= '0';
loop_next <= '0';
loop_iter <= (others => '0');
wave_inverted <= '0';

else

Expand All @@ -152,12 +153,12 @@ begin
if tick_cnt >= TZX_MS then
tick_cnt <= tick_cnt - TZX_MS;
wave_cnt <= wave_cnt + 1;
if wave_cnt = pulse_len then
if wave_cnt = pulse_len - 1 then
wave_cnt <= (others => '0');
cass_read <= wave_period;
wave_period <= not wave_period;
if wave_period = end_period then
pulse_len <= (others => '0');
else
wave_period <= not wave_period;
end if;
end if;
end if;
Expand All @@ -178,7 +179,8 @@ begin

case tzx_state is
when TZX_HEADER =>
cass_read <= '1';
wave_period <= '1';
wave_inverted <= '0';
tzx_offset <= tzx_offset + 1;
if tzx_offset = x"0A" then -- skip 9 bytes, offset lags 1
tzx_state <= TZX_NEWBLOCK;
Expand Down Expand Up @@ -253,9 +255,9 @@ begin
ms_counter <= ms_counter - 1;
-- Set pulse level to low after 1 ms
if ms_counter = 1 then
wave_inverted <= '0';
wave_period <= '0';
end_period <= '0';
cass_read <= '0';
end if;
end if;
elsif pause_len /= 0 then
Expand Down Expand Up @@ -346,7 +348,13 @@ begin
tzx_state <= TZX_NEWBLOCK;
else
pilot_pulses <= pilot_pulses - 1;
end_period <= wave_period;
if wave_inverted = '0' then
wave_period <= not wave_period;
end_period <= not wave_period; -- request pulse
else
wave_inverted <= '0';
end_period <= wave_period;
end if;
pulse_len <= pilot_l;
end if;
end if;
Expand All @@ -358,7 +366,13 @@ begin
elsif tzx_offset = x"01" then one_l( 7 downto 0) <= tap_fifo_do;
elsif tzx_offset = x"02" then
tzx_req <= tzx_ack; -- don't request new byte
end_period <= wave_period;
if wave_inverted = '0' then
wave_period <= not wave_period;
end_period <= not wave_period; -- request pulse
else
wave_inverted <= '0';
end_period <= wave_period;
end if;
pulse_len <= tap_fifo_do & one_l( 7 downto 0);
elsif tzx_offset = x"03" then
if data_len(7 downto 0) = x"01" then
Expand Down Expand Up @@ -432,23 +446,26 @@ begin

when TZX_PLAY_TONE =>
tzx_req <= tzx_ack; -- don't request new byte
end_period <= not wave_period;
wave_period <= not wave_period;
end_period <= not wave_period; -- request pulse
pulse_len <= pilot_l;
if pilot_pulses /= 0 then
pilot_pulses <= pilot_pulses - 1;
else
if pilot_pulses = 1 then
tzx_state <= TZX_PLAY_SYNC1;
else
pilot_pulses <= pilot_pulses - 1;
end if;

when TZX_PLAY_SYNC1 =>
tzx_req <= tzx_ack; -- don't request new byte
end_period <= wave_period;
wave_period <= not wave_period;
end_period <= not wave_period; -- request pulse
pulse_len <= sync1_l;
tzx_state <= TZX_PLAY_SYNC2;

when TZX_PLAY_SYNC2 =>
tzx_req <= tzx_ack; -- don't request new byte
end_period <= wave_period;
wave_period <= not wave_period;
end_period <= not wave_period; -- request pulse
pulse_len <= sync2_l;
tzx_state <= TZX_PLAY_TAPBLOCK;

Expand All @@ -463,7 +480,8 @@ begin
data_len <= data_len - 1;
tzx_state <= TZX_PLAY_TAPBLOCK3;
end if;
end_period <= not wave_period;
wave_period <= not wave_period;
end_period <= wave_period; -- request full period
if tap_fifo_do(CONV_INTEGER(bit_cnt)) = '0' then
pulse_len <= zero_l;
else
Expand All @@ -472,6 +490,8 @@ begin

when TZX_PLAY_TAPBLOCK3 =>
if data_len = 0 then
wave_period <= not wave_period;
wave_inverted <= '1';
tzx_state <= TZX_PAUSE2;
else
tzx_state <= TZX_PLAY_TAPBLOCK4;
Expand Down Expand Up @@ -505,12 +525,12 @@ begin
end if;

pulse_len <= zero_l;
cass_read <= tap_fifo_do(CONV_INTEGER(bit_cnt));
wave_period <= tap_fifo_do(CONV_INTEGER(bit_cnt));
end_period <= tap_fifo_do(CONV_INTEGER(bit_cnt));

when TZX_DIRECT3 =>
if data_len = 0 then
wave_inverted <= '0';
tzx_state <= TZX_PAUSE2;
else
tzx_state <= TZX_DIRECT2;
Expand Down

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