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Use lower-prio IRQ on Pico to decompress AAC/MP3 #85

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Merged
earlephilhower merged 1 commit into from
Oct 27, 2025
Merged

Use lower-prio IRQ on Pico to decompress AAC/MP3 #85

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46 changes: 42 additions & 4 deletions src/BackgroundAudioAAC.h
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Original file line number Diff line number Diff line change
Expand Up @@ -91,6 +91,14 @@ class BackgroundAudioAACClass {
return false;
}

#ifdef ARDUINO_ARCH_RP2040
_workIRQ = user_irq_claim_unused(true);
_workObj = this;
irq_set_exclusive_handler(_workIRQ, _irqStub);
irq_set_priority(_workIRQ, 0xc0); // Lowest prio
irq_set_enabled(_workIRQ, true);
#endif

_hAACDecoder = AACInitDecoderPre(_private, sizeof(_private));
if (!_hAACDecoder) {
return false;
Expand Down Expand Up @@ -119,6 +127,10 @@ class BackgroundAudioAACClass {
*/
void end() {
if (_playing) {
#ifdef ARDUINO_ARCH_RP2040
irq_set_enabled(_workIRQ, false);
user_irq_unclaim(_workIRQ);
#endif
_out->end();
}
}
Expand Down Expand Up @@ -205,7 +217,7 @@ class BackgroundAudioAACClass {
}

/**
@brief Get the number of times the MP3 decoder has underflowed waiting on raw data since `begin`
@brief Get the number of times the AAC decoder has underflowed waiting on raw data since `begin`

@return Number of frames of underflow data have occurred
*/
Expand All @@ -232,11 +244,11 @@ class BackgroundAudioAACClass {
}

/**
@brief Flushes any existing raw data, resets the processor to start a new MP3
@brief Flushes any existing raw data, resets the processor to start a new AAC

@details
This is only needed to abort a currently playing MP3 file (i.e. skipping a track in the middle).
Multiple MP3 files can just be concatenated together in the input buffer with `write`
This is only needed to abort a currently playing AAC file (i.e. skipping a track in the middle).
Multiple AAC files can just be concatenated together in the input buffer with `write`
*/
void flush() {
noInterrupts();
Expand Down Expand Up @@ -269,9 +281,20 @@ class BackgroundAudioAACClass {
}

private:
#ifdef ARDUINO_ARCH_RP2040
static void _irqStub() {
BackgroundAudioAACClass<DataBuffer>::_workObj->pump();
}

static void _cb(void *ptr) {
// Don't actually do work in the DMA interrupt, do it in the work IRQ context (low prio)
irq_set_pending(BackgroundAudioAACClass<DataBuffer>::_workIRQ);
}
#else
static void _cb(void *ptr) {
((BackgroundAudioAACClass*)ptr)->pump();
}
#endif

void generateOneFrame() {
// Every frame requires shifting all remaining data (6K?) before processing.
Expand Down Expand Up @@ -322,6 +345,9 @@ class BackgroundAudioAACClass {
ApplyGain((int16_t *)_outSample, _outSamples * 2, _gain);
}

#ifdef ARDUINO_ARCH_RP2040
public:
#endif
void pump() {
while (_out->availableForWrite() >= (int)(framelen * 2 * sizeof(int16_t))) {
if (_paused) {
Expand All @@ -334,8 +360,16 @@ class BackgroundAudioAACClass {
}
assert(_out->write((uint8_t *)_outSample, _outSamples * 2 * sizeof(int16_t)) == _outSamples * 2 * sizeof(int16_t));
}
#ifdef ARDUINO_ARCH_RP2040
irq_clear(_workIRQ);
#endif
}

#ifdef ARDUINO_ARCH_RP2040
static uint8_t _workIRQ;
static BackgroundAudioAACClass<DataBuffer> *_workObj;
#endif

private:
AudioOutputBase *_out = nullptr;
HAACDecoder _hAACDecoder;
Expand All @@ -358,6 +392,10 @@ class BackgroundAudioAACClass {
uint32_t _dumps = 0;
};

#ifdef ARDUINO_ARCH_RP2040
template<class DataBuffer> uint8_t BackgroundAudioAACClass<DataBuffer>::_workIRQ;
template<class DataBuffer> BackgroundAudioAACClass<DataBuffer> *BackgroundAudioAACClass<DataBuffer>::_workObj;
#endif

/**
@brief General purpose AAC background player with an 8KB buffer. Needs to have `write` called repeatedly with data.
Expand Down
45 changes: 45 additions & 0 deletions src/BackgroundAudioMP3.h
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Original file line number Diff line number Diff line change
Expand Up @@ -79,12 +79,26 @@ class BackgroundAudioMP3Class {
}




/**
@brief Starts the background MP3 decoder/player. Will initialize the output device and start sending silence immediately.

@return True on success, false if already started.
*/
bool begin() {
if (_playing || !_out) {
return false;
}

#ifdef ARDUINO_ARCH_RP2040
_workIRQ = user_irq_claim_unused(true);
_workObj = this;
irq_set_exclusive_handler(_workIRQ, _irqStub);
irq_set_priority(_workIRQ, 0xc0); // Lowest prio
irq_set_enabled(_workIRQ, true);
#endif

// MP3 processing init
mad_stream_init(&_stream);
mad_frame_init(&_frame);
Expand Down Expand Up @@ -115,6 +129,10 @@ class BackgroundAudioMP3Class {
*/
void end() {
if (_playing) {
#ifdef ARDUINO_ARCH_RP2040
irq_set_enabled(_workIRQ, false);
user_irq_unclaim(_workIRQ);
#endif
_out->end();
}
_playing = false;
Expand Down Expand Up @@ -268,9 +286,20 @@ class BackgroundAudioMP3Class {
}

private:
#ifdef ARDUINO_ARCH_RP2040
static void _irqStub() {
BackgroundAudioMP3Class<DataBuffer>::_workObj->pump();
}

static void _cb(void *ptr) {
// Don't actually do work in the DMA interrupt, do it in the work IRQ context (low prio)
irq_set_pending(BackgroundAudioMP3Class<DataBuffer>::_workIRQ);
}
#else
static void _cb(void *ptr) {
((BackgroundAudioMP3Class*)ptr)->pump();
}
#endif

void generateOneFrame() {
// Every frame requires shifting all remaining data (6K?) before processing.
Expand Down Expand Up @@ -341,6 +370,9 @@ class BackgroundAudioMP3Class {
ApplyGain((int16_t*)_synth.pcm.samplesX, framelen * 2, _gain);
}

#ifdef ARDUINO_ARCH_RP2040
public:
#endif
void pump() {
while (_out->availableForWrite() >= (int)(framelen * 4)) {
if (_paused) {
Expand All @@ -353,12 +385,21 @@ class BackgroundAudioMP3Class {
}
assert(_out->write((uint8_t *)_synth.pcm.samplesX, _synth.pcm.length * 4) == _synth.pcm.length * 4);
}
#ifdef ARDUINO_ARCH_RP2040
irq_clear(_workIRQ);
#endif
}

#ifdef ARDUINO_ARCH_RP2040
static uint8_t _workIRQ;
static BackgroundAudioMP3Class<DataBuffer> *_workObj;
#endif

private:
AudioOutputBase *_out;
bool _playing = false;
bool _paused = false;

static const size_t framelen = 1152;
static const size_t maxFrameSize = 2881;
DataBuffer _ib;
Expand All @@ -376,6 +417,10 @@ class BackgroundAudioMP3Class {
uint32_t _dumps = 0;
};

#ifdef ARDUINO_ARCH_RP2040
template<class DataBuffer> uint8_t BackgroundAudioMP3Class<DataBuffer>::_workIRQ;
template<class DataBuffer> BackgroundAudioMP3Class<DataBuffer> *BackgroundAudioMP3Class<DataBuffer>::_workObj;
#endif

/**
@brief General purpose MP3 background player with an 8KB buffer. Needs to have `write` called repeatedly with data.
Expand Down