AudioFlinger: re-add viper optimizations

These make a notable difference when playing audio on ESP32.

Without them, each UI action causes a stutter, so it's not fun to listen
to audio while doing anything on the device. With them, most UI actions don't
cause a stutter. Long maxed out CPU runs and storage access still do, though.

CHANGELOG.md

@@ -1,7 +1,8 @@
 0.5.1
 =====
-- Fri3d Camp 2024 Badge: workaround ADC2+WiFi conflict by temporarily disable WiFi to measure battery level
-- Fri3d Camp 2024 Badge: improve battery monitor calibration to fix 0.1V delta
+- Fri3d Camp 2024 Board: add startup light and sound
+- Fri3d Camp 2024 Board: workaround ADC2+WiFi conflict by temporarily disable WiFi to measure battery level
+- Fri3d Camp 2024 Board: improve battery monitor calibration to fix 0.1V delta
 - API: improve and cleanup animations
 - API: SharedPreferences: add erase_all() function
 - API: add defaults handling to SharedPreferences and only save non-defaults

internal_filesystem/lib/mpos/audio/stream_wav.py

@@ -7,14 +7,16 @@ import os
 import time
 import sys
 
-# Volume scaling function - regular Python version
-# Note: Viper optimization removed because @micropython.viper decorator
-# causes cross-compiler errors on Unix/macOS builds even inside conditionals
-def _scale_audio(buf, num_bytes, scale_fixed):
-    """Volume scaling for 16-bit audio samples."""
+# 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.
+import micropython
+@micropython.viper
+def _scale_audio(buf: ptr8, num_bytes: int, scale_fixed: int):
+    """Fast volume scaling for 16-bit audio samples using Viper (ESP32 native code emitter)."""
     for i in range(0, num_bytes, 2):
-        lo = buf[i]
-        hi = buf[i + 1]
+        lo = int(buf[i])
+        hi = int(buf[i + 1])
         sample = (hi << 8) | lo
         if hi & 128:
             sample -= 65536

scripts/build_mpos.sh

@@ -101,12 +101,23 @@ if [ "$target" == "esp32" ]; then
 elif [ "$target" == "unix" -o "$target" == "macOS" ]; then
 	manifest=$(readlink -f "$codebasedir"/manifests/manifest.py)
 	frozenmanifest="FROZEN_MANIFEST=$manifest"
+
+	# Comment out @micropython.viper decorator for Unix/macOS builds
+	# (cross-compiler doesn't support Viper native code emitter)
+	echo "Temporarily commenting out @micropython.viper decorator for Unix/macOS build..."
+	stream_wav_file="$codebasedir"/internal_filesystem/lib/mpos/audio/stream_wav.py
+	sed -i 's/^@micropython\.viper$/#@micropython.viper/' "$stream_wav_file"
+
 	# LV_CFLAGS are passed to USER_C_MODULES
 	# STRIP= makes it so that debug symbols are kept
 	pushd "$codebasedir"/lvgl_micropython/
 	# USER_C_MODULE doesn't seem to work properly so there are symlinks in lvgl_micropython/extmod/
 	python3 make.py "$target" LV_CFLAGS="-g -O0 -ggdb -ljpeg" STRIP=  DISPLAY=sdl_display INDEV=sdl_pointer INDEV=sdl_keyboard "$frozenmanifest"
 	popd
+
+	# Restore @micropython.viper decorator after build
+	echo "Restoring @micropython.viper decorator..."
+	sed -i 's/^#@micropython\.viper$/@micropython.viper/' "$stream_wav_file"
 else
 	echo "invalid target $target"
 fi