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This commit is contained in:
Davide Cavagnola
2025-05-27 17:42:40 +02:00
parent d1cfa6443b
commit 82d76e48d8
15 changed files with 1626 additions and 1047 deletions
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LAB3/src/volume_saturator.vhd
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@@ -2,80 +2,123 @@ LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
USE IEEE.NUMERIC_STD.ALL;
-- Entity: volume_saturator
-- Purpose: Second stage of volume control pipeline - clips multiplication results to prevent overflow
-- Reduces bit width from extended multiplier output back to original audio format
-- Implements saturation (clipping) to prevent audio distortion from mathematical overflow
ENTITY volume_saturator IS
GENERIC (
TDATA_WIDTH : POSITIVE := 24;
VOLUME_WIDTH : POSITIVE := 10;
VOLUME_STEP_2 : POSITIVE := 6; -- i.e., number_of_steps = 2**(VOLUME_STEP_2)
HIGHER_BOUND : INTEGER := 2 ** 15 - 1; -- Inclusive
LOWER_BOUND : INTEGER := - 2 ** 15 -- Inclusive
);
PORT (
aclk : IN STD_LOGIC;
aresetn : IN STD_LOGIC;
GENERIC (
TDATA_WIDTH : POSITIVE := 24; -- Width of final audio data output (24-bit audio samples)
VOLUME_WIDTH : POSITIVE := 10; -- Width of volume control input (10-bit = 0-1023 range)
VOLUME_STEP_2 : POSITIVE := 6; -- Log2 of volume values per step (2^6 = 64 values per step)
HIGHER_BOUND : INTEGER := 2 ** 15 - 1; -- Maximum positive value for saturation (inclusive)
LOWER_BOUND : INTEGER := - 2 ** 15 -- Maximum negative value for saturation (inclusive)
);
PORT (
-- Clock and reset signals
aclk : IN STD_LOGIC; -- Main clock input
aresetn : IN STD_LOGIC; -- Active-low asynchronous reset
s_axis_tvalid : IN STD_LOGIC;
s_axis_tdata : IN STD_LOGIC_VECTOR(TDATA_WIDTH - 1 + 2 ** (VOLUME_WIDTH - VOLUME_STEP_2 - 1) DOWNTO 0);
s_axis_tlast : IN STD_LOGIC;
s_axis_tready : OUT STD_LOGIC;
-- AXI4-Stream Slave Interface (Extended width input from multiplier)
s_axis_tvalid : IN STD_LOGIC; -- Input data valid signal
s_axis_tdata : IN STD_LOGIC_VECTOR(TDATA_WIDTH - 1 + 2 ** (VOLUME_WIDTH - VOLUME_STEP_2 - 1) DOWNTO 0); -- Wide input data from multiplier
s_axis_tlast : IN STD_LOGIC; -- Channel indicator (0=left, 1=right)
s_axis_tready : OUT STD_LOGIC; -- Ready to accept input data
m_axis_tvalid : OUT STD_LOGIC;
m_axis_tdata : OUT STD_LOGIC_VECTOR(TDATA_WIDTH - 1 DOWNTO 0);
m_axis_tlast : OUT STD_LOGIC;
m_axis_tready : IN STD_LOGIC
);
-- AXI4-Stream Master Interface (Original width output for audio)
m_axis_tvalid : OUT STD_LOGIC; -- Output data valid signal
m_axis_tdata : OUT STD_LOGIC_VECTOR(TDATA_WIDTH - 1 DOWNTO 0); -- Saturated audio sample output
m_axis_tlast : OUT STD_LOGIC; -- Channel indicator passthrough
m_axis_tready : IN STD_LOGIC -- Downstream ready signal
);
END volume_saturator;
ARCHITECTURE Behavioral OF volume_saturator IS
CONSTANT HIGHER_BOUND_VEC : STD_LOGIC_VECTOR(TDATA_WIDTH - 1 DOWNTO 0) := STD_LOGIC_VECTOR(to_signed(HIGHER_BOUND, TDATA_WIDTH));
CONSTANT LOWER_BOUND_VEC : STD_LOGIC_VECTOR(TDATA_WIDTH - 1 DOWNTO 0) := STD_LOGIC_VECTOR(to_signed(LOWER_BOUND, TDATA_WIDTH));
-- Pre-calculated saturation bounds as STD_LOGIC_VECTORS for efficient comparison
-- These constants define the valid range for audio samples after volume processing
CONSTANT HIGHER_BOUND_VEC : STD_LOGIC_VECTOR(TDATA_WIDTH - 1 DOWNTO 0) := STD_LOGIC_VECTOR(to_signed(HIGHER_BOUND, TDATA_WIDTH));
CONSTANT LOWER_BOUND_VEC : STD_LOGIC_VECTOR(TDATA_WIDTH - 1 DOWNTO 0) := STD_LOGIC_VECTOR(to_signed(LOWER_BOUND, TDATA_WIDTH));
SIGNAL m_axis_tvalid_int : STD_LOGIC;
-- Internal AXI4-Stream control signal
SIGNAL m_axis_tvalid_int : STD_LOGIC;
BEGIN
-- Output assignments
m_axis_tvalid <= m_axis_tvalid_int;
s_axis_tready <= (m_axis_tready OR NOT m_axis_tvalid_int) AND aresetn;
PROCESS (aclk)
BEGIN
-- Connect internal signals to output ports
m_axis_tvalid <= m_axis_tvalid_int;
-- Input ready logic: Ready when downstream is ready OR no valid data pending, AND not in reset
-- This implements proper AXI4-Stream backpressure handling
s_axis_tready <= (m_axis_tready OR NOT m_axis_tvalid_int) AND aresetn;
IF rising_edge(aclk) THEN
-- Main saturation and data processing logic
PROCESS (aclk)
BEGIN
IF aresetn = '0' THEN
m_axis_tvalid_int <= '0';
m_axis_tlast <= '0';
IF rising_edge(aclk) THEN
ELSE
-- Clear valid flag when master interface is ready
IF m_axis_tready = '1' THEN
m_axis_tvalid_int <= '0';
END IF;
IF aresetn = '0' THEN
-- Reset output interface
m_axis_tvalid_int <= '0'; -- No valid output data during reset
m_axis_tlast <= '0'; -- Clear channel indicator
-- Handle the data flow
IF s_axis_tvalid = '1' AND m_axis_tready = '1' THEN
-- Check if the input data is within the bounds else saturate
IF signed(s_axis_tdata) > signed(HIGHER_BOUND_VEC) THEN
m_axis_tdata <= HIGHER_BOUND_VEC;
ELSE
-- Normal operation
ELSIF signed(s_axis_tdata) < signed(LOWER_BOUND_VEC) THEN
m_axis_tdata <= LOWER_BOUND_VEC;
-- Output handshake management:
-- Clear valid flag when downstream accepts data
IF m_axis_tready = '1' THEN
m_axis_tvalid_int <= '0';
END IF;
ELSE
m_axis_tdata <= STD_LOGIC_VECTOR(resize(signed(s_axis_tdata), TDATA_WIDTH));
END IF;
-- Data processing: Apply saturation when both input and output are ready
IF s_axis_tvalid = '1' AND m_axis_tready = '1' THEN
-- Saturation Logic:
-- Check if the wide input data exceeds the valid audio range
-- If so, clip (saturate) to the nearest valid value
-- This prevents overflow distortion while preserving audio quality
IF signed(s_axis_tdata) > signed(HIGHER_BOUND_VEC) THEN
-- Positive overflow: Clip to maximum positive value
-- This prevents "wraparound" distortion from mathematical overflow
m_axis_tdata <= HIGHER_BOUND_VEC;
m_axis_tvalid_int <= '1';
m_axis_tlast <= s_axis_tlast;
ELSIF signed(s_axis_tdata) < signed(LOWER_BOUND_VEC) THEN
-- Negative overflow: Clip to maximum negative value
-- This prevents "wraparound" distortion from mathematical underflow
m_axis_tdata <= LOWER_BOUND_VEC;
END IF;
ELSE
-- Value within valid range: Resize to output width without clipping
-- This preserves the original audio quality when no overflow occurs
m_axis_tdata <= STD_LOGIC_VECTOR(resize(signed(s_axis_tdata), TDATA_WIDTH));
END IF;
END IF;
-- Set output control signals
m_axis_tvalid_int <= '1'; -- Mark output data as valid
m_axis_tlast <= s_axis_tlast; -- Pass through channel indicator
END IF;
END IF;
END PROCESS;
END IF;
END IF;
END PROCESS;
-- Saturation Purpose and Benefits:
-- 1. Prevents audio distortion from mathematical overflow
-- 2. Maintains audio dynamic range within valid bit representation
-- 3. Reduces wide multiplication results back to standard audio format
-- 4. Provides "soft limiting" behavior for volume control
-- 5. Ensures compatibility with downstream audio processing blocks
--
-- Without saturation, volume amplification could cause:
-- - Mathematical overflow leading to sign bit flips
-- - Severe audio distortion (crackling, popping sounds)
-- - Invalid audio sample values outside the representable range
END Behavioral;