Add support for 8 channel I2S mono audio output on RPi 5 (#657)

* First implementation of using four PCM5102 I2S sound devices for 8-channel mono sound output on a Raspberry Pi 5.  Requires latest develop branch of circle.

* Update to required develop branch of circle

* Adjusted default chunk sizes to correctly support number of channels.

* Update queue size as per Rene's suggestion.

---------

Co-authored-by: probonopd <probonopd@users.noreply.github.com>

src/config.cpp

@@ -41,11 +41,18 @@ void CConfig::Load (void)
 	m_SoundDevice = m_Properties.GetString ("SoundDevice", "pwm");
 
 	m_nSampleRate = m_Properties.GetNumber ("SampleRate", 48000);
+	m_bQuadDAC8Chan = m_Properties.GetNumber ("QuadDAC8Chan", 0) != 0;
+	if (m_SoundDevice == "hdmi") {
+		m_nChunkSize = m_Properties.GetNumber ("ChunkSize", 384*6);
+	}
+	else
+	{
 #ifdef ARM_ALLOW_MULTI_CORE
-	m_nChunkSize = m_Properties.GetNumber ("ChunkSize", m_SoundDevice == "hdmi" ? 384*6 : 256);
+		m_nChunkSize = m_Properties.GetNumber ("ChunkSize", m_bQuadDAC8Chan ? 1024 : 256);  // 128 per channel
 #else
-	m_nChunkSize = m_Properties.GetNumber ("ChunkSize", m_SoundDevice == "hdmi" ? 384*6 : 1024);
+		m_nChunkSize = m_Properties.GetNumber ("ChunkSize", 1024);
 #endif
+	}
 	m_nDACI2CAddress = m_Properties.GetNumber ("DACI2CAddress", 0);
 	m_bChannelsSwapped = m_Properties.GetNumber ("ChannelsSwapped", 0) != 0;
 
@@ -243,6 +250,11 @@ bool CConfig::GetExpandPCAcrossBanks (void) const
 	return m_bExpandPCAcrossBanks;
 }
 
+bool CConfig::GetQuadDAC8Chan (void) const
+{
+	return m_bQuadDAC8Chan;
+}
+
 bool CConfig::GetLCDEnabled (void) const
 {
 	return m_bLCDEnabled;

src/config.h

@@ -87,6 +87,7 @@ public:
 	bool GetMIDIAutoVoiceDumpOnPC (void) const; // false if not specified
 	bool GetHeaderlessSysExVoices (void) const; // false if not specified
 	bool GetExpandPCAcrossBanks (void) const; // true if not specified
+	bool GetQuadDAC8Chan (void) const; // false if not specified
 
 	// HD44780 LCD
 	// GPIO pin numbers are chip numbers, not header positions
@@ -208,6 +209,7 @@ private:
 	bool m_bMIDIAutoVoiceDumpOnPC;
 	bool m_bHeaderlessSysExVoices;
 	bool m_bExpandPCAcrossBanks;
+	bool m_bQuadDAC8Chan;
 
 	bool m_bLCDEnabled;
 	unsigned m_nLCDPinEnable;

src/minidexed.cpp

@@ -42,6 +42,7 @@ CMiniDexed::CMiniDexed (CConfig *pConfig, CInterruptSystem *pInterrupt,
 	m_PCKeyboard (this, pConfig, &m_UI),
 	m_SerialMIDI (this, pInterrupt, pConfig, &m_UI),
 	m_bUseSerial (false),
+	m_bQuadDAC8Chan (false),
 	m_pSoundDevice (0),
 	m_bChannelsSwapped (pConfig->GetChannelsSwapped ()),
 #ifdef ARM_ALLOW_MULTI_CORE
@@ -125,10 +126,26 @@ CMiniDexed::CMiniDexed (CConfig *pConfig, CInterruptSystem *pInterrupt,
 	if (strcmp (pDeviceName, "i2s") == 0)
 	{
 		LOGNOTE ("I2S mode");
-
+#if RASPPI==5
+		// Quad DAC 8-channel mono only an option for RPI 5
+		m_bQuadDAC8Chan = pConfig->GetQuadDAC8Chan ();
+#endif
+		if (m_bQuadDAC8Chan) {
+			LOGNOTE ("Configured for Quad DAC 8-channel Mono audio");
+			m_pSoundDevice = new CI2SSoundBaseDevice (pInterrupt, pConfig->GetSampleRate (),
+								  pConfig->GetChunkSize (), false,
+								  pI2CMaster, pConfig->GetDACI2CAddress (),
+								  CI2SSoundBaseDevice::DeviceModeTXOnly,
+								  8);  // 8 channels - L+R x4 across 4 I2S lanes
+		}
+		else
+		{
 			m_pSoundDevice = new CI2SSoundBaseDevice (pInterrupt, pConfig->GetSampleRate (),
 								  pConfig->GetChunkSize (), false,
-							  pI2CMaster, pConfig->GetDACI2CAddress ());
+								  pI2CMaster, pConfig->GetDACI2CAddress (),
+								  CI2SSoundBaseDevice::DeviceModeTXOnly,
+								  2);  // 2 channels - L+R
+		}
 	}
 	else if (strcmp (pDeviceName, "hdmi") == 0)
 	{
@@ -251,18 +268,30 @@ bool CMiniDexed::Initialize (void)
 	}
 	
 	// setup and start the sound device
-	if (!m_pSoundDevice->AllocateQueueFrames (m_pConfig->GetChunkSize ()))
+	int Channels = 1;	// 16-bit Mono
+#ifdef ARM_ALLOW_MULTI_CORE
+	if (m_bQuadDAC8Chan)
+	{
+		Channels = 8;	// 16-bit 8-channel mono
+	}
+	else
+	{
+		Channels = 2;	// 16-bit Stereo
+	}
+#endif
+	// Need 2 x ChunkSize / Channel queue frames as the audio driver uses
+	// two DMA channels each of ChunkSize and one single single frame
+	// contains a sample for each of all the channels.
+	//
+	// See discussion here: https://github.com/rsta2/circle/discussions/453
+	if (!m_pSoundDevice->AllocateQueueFrames (2 * m_pConfig->GetChunkSize () / Channels))
 	{
 		LOGERR ("Cannot allocate sound queue");
 
 		return false;
 	}
 
-#ifndef ARM_ALLOW_MULTI_CORE
-	m_pSoundDevice->SetWriteFormat (SoundFormatSigned16, 1);	// 16-bit Mono
-#else
-	m_pSoundDevice->SetWriteFormat (SoundFormatSigned16, 2);	// 16-bit Stereo
-#endif
+	m_pSoundDevice->SetWriteFormat (SoundFormatSigned16, Channels);
 
 	m_nQueueSizeFrames = m_pSoundDevice->GetQueueSizeFrames ();
 
@@ -1128,6 +1157,48 @@ void CMiniDexed::ProcessSound (void)
 
 		assert (CConfig::ToneGenerators == 8);
 
+		if (m_bQuadDAC8Chan) {
+			// No mixing is performed by MiniDexed, sound is output in 8 channels.
+			// Note: one TG per audio channel; output=mono; no processing.
+			const int Channels = 8;  // One TG per channel
+			float32_t tmp_float[nFrames*Channels];
+			int16_t tmp_int[nFrames*Channels];
+
+			if(nMasterVolume > 0.0)
+			{
+				// Convert dual float array (8 chan) to single int16 array (8 chan)
+				for(uint16_t i=0; i<nFrames;i++)
+				{
+					// TGs will alternate on L/R channels for each output
+					// reading directly from the TG OutputLevel buffer with
+					// no additional processing.
+					for (uint8_t tg = 0; tg < Channels; tg++)
+					{
+						if(nMasterVolume >0.0 && nMasterVolume <1.0)
+						{
+							tmp_float[(i*Channels)+tg]=m_OutputLevel[tg][i] * nMasterVolume;
+						}
+						else if(nMasterVolume == 1.0)
+						{
+							tmp_float[(i*Channels)+tg]=m_OutputLevel[tg][i];
+						}
+					}
+				}
+				arm_float_to_q15(tmp_float,tmp_int,nFrames*Channels);
+			}
+			else
+			{
+				arm_fill_q15(0, tmp_int, nFrames*Channels);
+			}
+
+			if (m_pSoundDevice->Write (tmp_int, sizeof(tmp_int)) != (int) sizeof(tmp_int))
+			{
+				LOGERR ("Sound data dropped");
+			}
+		}
+		else
+		{
+			// Mix everything down to stereo		
 			uint8_t indexL=0, indexR=1;
 
 			// BEGIN TG mixing
@@ -1201,12 +1272,15 @@ void CMiniDexed::ProcessSound (void)
 				arm_float_to_q15(tmp_float,tmp_int,nFrames*2);
 			}
 			else
+			{
 				arm_fill_q15(0, tmp_int, nFrames * 2);
+			}
 
 			if (m_pSoundDevice->Write (tmp_int, sizeof(tmp_int)) != (int) sizeof(tmp_int))
 			{
 				LOGERR ("Sound data dropped");
 			}
+		} // End of Stereo mixing
 
 		if (m_bProfileEnabled)
 		{

src/minidexed.h

@@ -298,6 +298,7 @@ private:
 	CPCKeyboard m_PCKeyboard;
 	CSerialMIDIDevice m_SerialMIDI;
 	bool m_bUseSerial;
+	bool m_bQuadDAC8Chan;
 
 	CSoundBaseDevice *m_pSoundDevice;
 	bool m_bChannelsSwapped;

submod.sh

@@ -12,7 +12,7 @@ cd -
 #
 # Optional update submodules explicitly
 cd circle-stdlib/libs/circle
-git checkout 4155f43
+git checkout fff3764
 cd -
 cd circle-stdlib/libs/circle-newlib
 #git checkout develop