Ignore note-ons received during SoundFont switch

Fixes #247.

CHANGELOG.md

@@ -25,6 +25,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - A bug in the config file reader (unterminated string) could cause the last entry in the file to be read as a corrupted value if the file ended without a newline.
 - Some FTP commands could work without being logged in.
 - Some DAC accessories which make use of a hardware "mute" pin (e.g. Adafruit I²S Audio Bonnet) could be held in a muted state due to a conflict with the Blokas Pisound driver's probing routine (issue #233). The driver now resets these GPIO pins to the initial power-on state, which should fix this issue. Thanks to @htamas2 for the report!
+- Sudden loud noise caused by switching SoundFonts whilst receiving MIDI data (issue #247). Any note-on messages received whilst busy switching SoundFonts are now discarded. Thanks to @c0d3h4x0r for the report!
 
 ## [0.11.0] - 2021-12-12
 

include/midiparser.h

@@ -30,7 +30,7 @@ class CMIDIParser
 public:
 	CMIDIParser();
 
-	void ParseMIDIBytes(const u8* pData, size_t nSize);
+	void ParseMIDIBytes(const u8* pData, size_t nSize, bool bIgnoreNoteOns = false);
 
 protected:
 	virtual void OnShortMessage(u32 nMessage) = 0;
@@ -51,7 +51,7 @@ class CMIDIParser
 	static constexpr size_t SysExBufferSize = 1000;
 
 	void ParseStatusByte(u8 nByte);
-	bool CheckCompleteShortMessage();
+	bool CheckCompleteShortMessage(bool bIgnoreNoteOns = false);
 	u32 PrepareShortMessage() const;
 	void ResetState(bool bClearStatusByte);
 

include/mt32pi.h

@@ -117,6 +117,7 @@ class CMT32Pi : CMultiCoreSupport, CPower, CMIDIParser, CAppleMIDIHandler
 	void UpdateUSB(bool bStartup = false);
 	void UpdateNetwork();
 	void UpdateMIDI();
+	void PurgeMIDIBuffers();
 	size_t ReceiveSerialMIDI(u8* pOutData, size_t nSize);
 	bool ParseCustomSysEx(const u8* pData, size_t nSize);
 

src/midiparser.cpp

@@ -33,7 +33,7 @@ CMIDIParser::CMIDIParser()
 {
 }
 
-void CMIDIParser::ParseMIDIBytes(const u8* pData, size_t nSize)
+void CMIDIParser::ParseMIDIBytes(const u8* pData, size_t nSize, bool bIgnoreNoteOns)
 {
 	// Process MIDI messages
 	// See: https://www.midi.org/specifications/item/table-1-summary-of-midi-message
@@ -71,7 +71,7 @@ void CMIDIParser::ParseMIDIBytes(const u8* pData, size_t nSize)
 				}
 
 				m_MessageBuffer[m_nMessageLength++] = nByte;
-				CheckCompleteShortMessage();
+				CheckCompleteShortMessage(bIgnoreNoteOns);
 				break;
 
 			// Expecting a SysEx data byte or EOX
@@ -167,7 +167,7 @@ void CMIDIParser::ParseStatusByte(u8 nByte)
 	}
 }
 
-bool CMIDIParser::CheckCompleteShortMessage()
+bool CMIDIParser::CheckCompleteShortMessage(bool bIgnoreNoteOns)
 {
 	const u8 nStatus = m_MessageBuffer[0];
 
@@ -176,7 +176,10 @@ bool CMIDIParser::CheckCompleteShortMessage()
 	if (m_nMessageLength == 3 ||
 		(m_nMessageLength == 2 && ((nStatus >= 0xC0 && nStatus <= 0xDF) || nStatus == 0xF1 || nStatus == 0xF3)))
 	{
-		OnShortMessage(PrepareShortMessage());
+		const bool bIsNoteOn = (nStatus & 0xF0) == 0x90;
+
+		if (!(bIsNoteOn && bIgnoreNoteOns))
+			OnShortMessage(PrepareShortMessage());
 
 		// Clear running status if System Common
 		ResetState(nStatus >= 0xF1 && nStatus <= 0xF7);

src/mt32pi.cpp

@@ -906,6 +906,22 @@ void CMT32Pi::UpdateMIDI()
 	s_pThis->m_nActiveSenseTime = s_pThis->m_pTimer->GetTicks();
 }
 
+void CMT32Pi::PurgeMIDIBuffers()
+{
+	size_t nBytes;
+	u8 Buffer[MIDIRxBufferSize];
+
+	// Process MIDI messages from all devices/ring buffers, but ignore note-ons
+	while (m_bSerialMIDIEnabled && (nBytes = ReceiveSerialMIDI(Buffer, sizeof(Buffer))) > 0)
+		ParseMIDIBytes(Buffer, nBytes, true);
+
+	while (m_pUSBSerialDevice && (nBytes = m_pUSBSerialDevice->Read(Buffer, sizeof(Buffer))) > 0)
+		ParseMIDIBytes(Buffer, nBytes, true);
+
+	while ((nBytes = m_MIDIRxBuffer.Dequeue(Buffer, sizeof(Buffer))) > 0)
+		ParseMIDIBytes(Buffer, nBytes, true);
+}
+
 size_t CMT32Pi::ReceiveSerialMIDI(u8* pOutData, size_t nSize)
 {
 	// Read serial MIDI data
@@ -1124,8 +1140,14 @@ void CMT32Pi::SwitchSoundFont(size_t nIndex)
 		return;
 
 	m_pLogger->Write(MT32PiName, LogNotice, "Switching to SoundFont %d", nIndex);
-	if (m_pSoundFontSynth->SwitchSoundFont(nIndex) && m_pCurrentSynth == m_pSoundFontSynth)
-		m_pSoundFontSynth->ReportStatus();
+	if (m_pSoundFontSynth->SwitchSoundFont(nIndex))
+	{
+		// Handle any MIDI data that has been queued up while busy
+		PurgeMIDIBuffers();
+
+		if (m_pCurrentSynth == m_pSoundFontSynth)
+			m_pSoundFontSynth->ReportStatus();
+	}
 }
 
 void CMT32Pi::DeferSwitchSoundFont(size_t nIndex)