225 lines
12 KiB
VHDL
225 lines
12 KiB
VHDL
LIBRARY IEEE;
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USE IEEE.STD_LOGIC_1164.ALL;
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USE IEEE.NUMERIC_STD.ALL;
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-- Entity: LFO (Low Frequency Oscillator) - Alternative Implementation
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-- Purpose: Applies effect to audio by modulating amplitude with a triangular wave
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-- This is a simplified, single-process implementation compared to the pipelined version
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-- Provides real-time audio amplitude modulation for musical effects
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ENTITY LFO IS
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GENERIC (
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CHANNEL_LENGHT : INTEGER := 24; -- Bit width of audio samples (24-bit signed)
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JOYSTICK_LENGHT : INTEGER := 10; -- Bit width of joystick input (10-bit = 0-1023 range)
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CLK_PERIOD_NS : INTEGER := 10; -- Clock period in nanoseconds (10ns = 100MHz)
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TRIANGULAR_COUNTER_LENGHT : INTEGER := 10 -- Triangular wave counter length (affects modulation depth)
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);
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PORT (
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-- Clock and Reset
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aclk : IN STD_LOGIC; -- Main system clock
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aresetn : IN STD_LOGIC; -- Active-low asynchronous reset
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-- LFO Control inputs
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lfo_period : IN STD_LOGIC_VECTOR(JOYSTICK_LENGHT - 1 DOWNTO 0); -- Controls LFO frequency (joystick Y-axis)
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lfo_enable : IN STD_LOGIC; -- Enable/bypass LFO effect
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-- Slave AXI Stream interface (audio input)
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s_axis_tvalid : IN STD_LOGIC; -- Input data valid signal
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s_axis_tdata : IN STD_LOGIC_VECTOR(CHANNEL_LENGHT - 1 DOWNTO 0); -- Audio sample input
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s_axis_tlast : IN STD_LOGIC; -- Channel indicator (0=left, 1=right)
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s_axis_tready : OUT STD_LOGIC; -- Ready to accept input data
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-- Master AXI Stream interface (audio output)
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m_axis_tvalid : OUT STD_LOGIC; -- Output data valid signal
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m_axis_tdata : OUT STD_LOGIC_VECTOR(CHANNEL_LENGHT - 1 DOWNTO 0); -- Modulated audio sample output
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m_axis_tlast : OUT STD_LOGIC; -- Channel indicator passthrough
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m_axis_tready : IN STD_LOGIC -- Downstream ready signal
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);
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END ENTITY LFO;
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ARCHITECTURE Behavioral OF LFO IS
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-- LFO timing configuration constants
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CONSTANT LFO_COUNTER_BASE_PERIOD_US : INTEGER := 1000; -- Base period: 1ms (1kHz base frequency)
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CONSTANT ADJUSTMENT_FACTOR : INTEGER := 90; -- Frequency adjustment sensitivity (clock cycles per joystick unit)
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CONSTANT JSTK_CENTER_VALUE : INTEGER := 2 ** (JOYSTICK_LENGHT - 1); -- Joystick center position (512 for 10-bit)
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-- Calculate base clock cycles for 1ms period at current clock frequency
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CONSTANT LFO_COUNTER_BASE_CLK_CYCLES : INTEGER := LFO_COUNTER_BASE_PERIOD_US * 1000 / CLK_PERIOD_NS; -- 1ms = 100,000 clk cycles
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-- Calculate frequency range limits based on joystick range
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CONSTANT LFO_CLK_CYCLES_MIN : INTEGER := LFO_COUNTER_BASE_CLK_CYCLES - ADJUSTMENT_FACTOR * (2 ** (JOYSTICK_LENGHT - 1)); -- 53,920 clk cycles (faster)
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CONSTANT LFO_CLK_CYCLES_MAX : INTEGER := LFO_COUNTER_BASE_CLK_CYCLES + ADJUSTMENT_FACTOR * (2 ** (JOYSTICK_LENGHT - 1) - 1); -- 145,990 clk cycles (slower)
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-- LFO timing control signals
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SIGNAL step_clk_cycles_delta : INTEGER RANGE - 2 ** (JOYSTICK_LENGHT - 1) * ADJUSTMENT_FACTOR TO (2 ** (JOYSTICK_LENGHT - 1) - 1) * ADJUSTMENT_FACTOR := 0;
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SIGNAL step_clk_cycles : INTEGER RANGE LFO_CLK_CYCLES_MIN TO LFO_CLK_CYCLES_MAX := LFO_COUNTER_BASE_CLK_CYCLES;
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SIGNAL step_counter : NATURAL RANGE 0 TO LFO_CLK_CYCLES_MAX := 0;
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-- Triangular wave generation signals
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-- Note: Using signed counter with extra bit to handle full range calculations
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SIGNAL tri_counter : SIGNED(TRIANGULAR_COUNTER_LENGHT DOWNTO 0) := (OTHERS => '0'); -- Triangular wave amplitude
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SIGNAL direction_up : STD_LOGIC := '1'; -- Wave direction: '1' = ascending, '0' = descending
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-- AXI4-Stream control signals
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SIGNAL trigger : STD_LOGIC := '0'; -- Trigger to indicate new processed data is ready
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SIGNAL s_axis_tlast_reg : STD_LOGIC := '0'; -- Registered version of tlast for output synchronization
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SIGNAL m_axis_tvalid_int : STD_LOGIC := '0'; -- Internal output valid signal
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-- Audio processing signal with extended width for multiplication
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-- Width accommodates: audio sample + triangular counter to prevent overflow
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SIGNAL m_axis_tdata_temp : SIGNED(CHANNEL_LENGHT + TRIANGULAR_COUNTER_LENGHT DOWNTO 0) := (OTHERS => '0');
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BEGIN
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-- Output signal assignments with proper AXI4-Stream flow control
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m_axis_tvalid <= m_axis_tvalid_int;
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-- Input ready logic: Ready when downstream is ready OR no valid data pending, AND not in reset
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s_axis_tready <= (m_axis_tready OR NOT m_axis_tvalid_int) AND aresetn;
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-- Optimized single process for LFO timing and triangular waveform generation
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-- This process handles both the frequency control and wave shape generation
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triangular_wave_lfo_generator : PROCESS (aclk)
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BEGIN
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IF rising_edge(aclk) THEN
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IF aresetn = '0' THEN
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-- Reset LFO generator to initial state
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step_clk_cycles <= LFO_COUNTER_BASE_CLK_CYCLES; -- Set to base frequency
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step_counter <= 0; -- Clear timing counter
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tri_counter <= (OTHERS => '0'); -- Start triangular wave at zero
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direction_up <= '1'; -- Start counting up
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ELSE
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-- Calculate LFO period based on joystick input
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-- Joystick mapping:
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-- 0-511: Slower than base frequency (longer period, lower frequency)
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-- 512: Base frequency (1kHz)
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-- 513-1023: Faster than base frequency (shorter period, higher frequency)
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step_clk_cycles_delta <= (to_integer(unsigned(lfo_period)) - JSTK_CENTER_VALUE);
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step_clk_cycles <= LFO_COUNTER_BASE_CLK_CYCLES - step_clk_cycles_delta * ADJUSTMENT_FACTOR;
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-- Generate triangular wave when LFO is enabled
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IF lfo_enable = '1' THEN
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-- Clock divider: Update triangular wave at calculated rate
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IF step_counter >= step_clk_cycles THEN
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step_counter <= 0; -- Reset counter for next period
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-- Check for triangular wave direction changes at extremes
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-- Note: Using (2^n - 2) and 1 instead of (2^n - 1) and 0 due to process signal assignment
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IF tri_counter = (2 ** TRIANGULAR_COUNTER_LENGHT) - 2 THEN
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direction_up <= '0'; -- Switch to descending at near-maximum
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ELSIF tri_counter = 1 THEN
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direction_up <= '1'; -- Switch to ascending at near-minimum
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END IF;
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-- Update triangular wave value based on current direction
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-- This creates the classic triangular waveform shape
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IF direction_up = '1' THEN
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tri_counter <= tri_counter + 1; -- Ascending: increment
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ELSE
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tri_counter <= tri_counter - 1; -- Descending: decrement
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END IF;
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ELSE
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step_counter <= step_counter + 1; -- Continue counting towards next update
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END IF;
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END IF;
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END IF;
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END IF;
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END PROCESS triangular_wave_lfo_generator;
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-- AXI4-Stream handshake logic and audio processing
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-- This process handles input/output data flow and applies the LFO modulation
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AXIS : PROCESS (aclk)
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BEGIN
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IF rising_edge(aclk) THEN
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IF aresetn = '0' THEN
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-- Reset AXI4-Stream interface and audio processing
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s_axis_tlast_reg <= '0'; -- Clear registered channel indicator
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m_axis_tdata_temp <= (OTHERS => '0'); -- Clear temporary audio data
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m_axis_tvalid_int <= '0'; -- No valid output data
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m_axis_tlast <= '0'; -- Clear output channel indicator
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ELSE
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-- Output handshake management:
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-- Clear valid flag when downstream accepts data
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IF m_axis_tready = '1' THEN
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m_axis_tvalid_int <= '0';
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END IF;
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-- Data output logic: Send processed audio when trigger is active and output is available
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IF trigger = '1' AND (m_axis_tvalid_int = '0' OR m_axis_tready = '1') THEN
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-- Scale down the multiplication result to original audio bit width
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-- Right shift by TRIANGULAR_COUNTER_LENGHT effectively divides by 2^TRIANGULAR_COUNTER_LENGHT
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-- This maintains proper audio amplitude after modulation
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m_axis_tdata <= STD_LOGIC_VECTOR(
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resize(
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shift_right(
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m_axis_tdata_temp, -- Wide multiplication result
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TRIANGULAR_COUNTER_LENGHT -- Scale factor
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),
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CHANNEL_LENGHT -- Final audio sample width
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)
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);
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m_axis_tlast <= s_axis_tlast_reg; -- Output registered channel indicator
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m_axis_tvalid_int <= '1'; -- Mark output as valid
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trigger <= '0'; -- Clear trigger - data has been output
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END IF;
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-- Data input logic: Process new audio samples when available and output is ready
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IF s_axis_tvalid = '1' AND (m_axis_tready = '1' OR m_axis_tvalid_int = '0') THEN
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IF lfo_enable = '1' THEN
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-- Apply LFO effect: multiply audio sample by triangular wave
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-- This creates amplitude modulation (effect)
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m_axis_tdata_temp <= signed(s_axis_tdata) * tri_counter;
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s_axis_tlast_reg <= s_axis_tlast; -- Register channel indicator
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ELSE
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-- LFO disabled: pass audio through unchanged but maintain bit width
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-- Left shift compensates for the right shift that occurs during output
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-- This ensures unity gain when LFO is bypassed
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m_axis_tdata_temp <= shift_left(
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resize(
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signed(s_axis_tdata), -- Convert input to signed
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m_axis_tdata_temp'length -- Extend to full processing width
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),
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TRIANGULAR_COUNTER_LENGHT -- Compensate for output scaling
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);
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s_axis_tlast_reg <= s_axis_tlast; -- Register channel indicator
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END IF;
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trigger <= '1'; -- Set trigger to indicate new processed data is ready
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END IF;
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END IF;
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END IF;
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END PROCESS AXIS;
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-- LFO Implementation Summary:
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-- 1. Generates triangular wave at frequency controlled by joystick input
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-- 2. When enabled: multiplies audio samples by triangular wave (multiplier value range from 0 to 1)
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-- 3. When disabled: passes audio through unchanged (bypass mode)
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-- 4. Uses proper AXI4-Stream handshaking for real-time audio processing
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--
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-- Effect Characteristics:
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-- - Frequency range: Approximately 0.1Hz to 10Hz (typical for audio LFO)
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-- - Modulation depth: Controlled by TRIANGULAR_COUNTER_LENGHT generic
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-- - Waveform: Triangular (linear amplitude changes, smooth transitions)
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-- - Bypass capability: Clean audio passthrough when disabled
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END ARCHITECTURE Behavioral; |