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stream_wav.py: add hardware volume control

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uses shift but doesn't seem to work
This commit is contained in:
Thomas Farstrike
2026-02-25 14:31:57 +01:00
parent 0cc1ca0ff4
commit 71e1ea8bd2
1 changed files with 39 additions and 3 deletions
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internal_filesystem/lib/mpos/audio/stream_wav.py
+39 -3
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@@ -8,6 +8,10 @@ import os
import sys
import time
# Toggle to enable I2S.shift-based volume scaling when available.
# Set to False to use legacy software scaling only.
USE_I2S_SHIFT_VOLUME = False
# Volume scaling function - Viper-optimized for ESP32 performance
# NOTE: The line below is automatically commented out by build_mpos.sh during
# Unix/macOS builds (cross-compiler doesn't support Viper), then uncommented after build.
@@ -141,6 +145,21 @@ def _scale_audio_powers_of_2(buf: ptr8, num_bytes: int, shift: int):
buf[i] = s & 0xFF
buf[i+1] = (s >> 8) & 0xFF
# Would be faster to use a lookup table here
def _volume_to_shift(scale_fixed):
"""Convert fixed-point volume (0..32768) to a right-shift amount (0..16)."""
if scale_fixed >= 32768:
return 0
if scale_fixed <= 0:
return 16
shift = 0
threshold = 32768
while shift < 16 and scale_fixed < threshold:
shift += 1
threshold >>= 1
return shift
class WAVStream:
"""
WAV file playback stream with I2S output.
@@ -400,8 +419,8 @@ class WAVStream:
)
self._playback_rate = playback_rate
#ibuf = playback_rate # doesnt account for stereo vs mono...
ibuf = 32000
# ibuf = playback_rate # doesnt account for stereo vs mono...
ibuf = 32000
print(f"WAVStream: {original_rate} Hz, {bits_per_sample}-bit, {channels}-ch")
print(f"WAVStream: Playback at {playback_rate} Hz (factor {upsample_factor})")
@@ -523,7 +542,24 @@ class WAVStream:
scale = self.volume / 100.0
if scale < 1.0:
scale_fixed = int(scale * 32768)
_scale_audio_optimized(raw, len(raw), scale_fixed)
if (
USE_I2S_SHIFT_VOLUME
and self._i2s
and hasattr(self._i2s, "shift")
):
shift = _volume_to_shift(scale_fixed)
if shift >= 16:
for i in range(len(raw)):
raw[i] = 0
elif shift > 0:
try:
self._i2s.shift(raw, 16, shift) # triggers exception
except Exception as e:
print(f"_i2s.shift got exception, falling back to software scaling: {e}")
_scale_audio_optimized(raw, len(raw), scale_fixed)
else:
print("_i2s has no shift attribute, falling back to software scaling")
_scale_audio_optimized(raw, len(raw), scale_fixed)
# 4. Output to I2S (blocking write is OK - we're in a separate thread)
if self._i2s: