Update comment

source/Mockingboard.cpp

@@ -405,9 +405,9 @@ bool MockingboardCard::Is6522IRQ(void)
 		irq |= m_MBSubUnit[i].sy6522.GetReg(SY6522::rIFR) & 0x80 ? true : false;
 
 	// NB. Mockingboard generates IRQ on both 6522s:
-	// . SSI263's IRQ (A/!R) is routed via the 2nd 6522 (at $Cn80) and must generate a 6502 IRQ (not NMI)
-	//   - NB. 2nd SSI263's IRQ is routed via the 1st 6522 (at $Cn00) and again generates a 6502 IRQ
-	// . SC-01's IRQ (A/!R) is routed via the 6522 at $Cn00 (NB. Only the Mockingboard "Sound/Speech I" card supports the SC-01)
+	// . SSI263's IRQ (A/!R) is routed via the 2nd 6522's CA1 input (at $Cn80) and must generate a 6502 IRQ (not NMI)
+	//   - NB. 2nd SSI263's IRQ is routed via the 1st 6522's CA1 input (at $Cn00) and again generates a 6502 IRQ
+	// . SC-01's IRQ (!A/R) is routed via the 6522 at $Cn00 (NB. Only the Mockingboard "Sound/Speech I" card supports the SC-01)
 	// Phasor's SSI263 IRQ (A/!R) line is *also* wired directly to the 6502's IRQ (as well as the 6522's CA1)
 
 	return irq;

source/SSI263.cpp

@@ -140,20 +140,10 @@ void SSI263::Write(BYTE nReg, BYTE nValue)
 	ssiRegs[nReg] = nValue;
 #endif
 
-	// Notes:
-	// . Phasor's text-to-speech playback has no CTL H->L
-	//		- ISR just writes CTL=0 (and new ART+AMP values), and writes DUR=x (and new PHON)
-	//		- since no CTL H->L, then DUR value doesn't take affect (so continue using previous)
-	//		- so the write to DURPHON must clear the IRQ
-	// . Does a write of CTL=0 clear IRQ? (ie. CTL 0->0)
-	// . Does a write of CTL=1 clear IRQ? (ie. CTL 0->1)
-	//		- SSI263 datasheet says: "Setting the Control bit (CTL) to a logic one puts the device into Power Down mode..."
-	// . Does phoneme output only happen when CTL=0? (Otherwise device is in PD mode)
-
-	// SSI263 datasheet is not clear, but a write to DURPHON must clear the IRQ.
-	// . Empirically writes to regs 0,1 & 2 all clear the IRQ (and writes to 3,4..7 don't) (GH#1197)
-	// NB. For Mockingboard, A/!R is ack'ed by 6522's PCR handshake and D7 is cleared.
-	if (m_cardMode == PH_Phasor && nReg <= SSI_RATEINF)
+	// SSI263 datasheet is not clear, but a write to DURPHON must de-assert the IRQ and clear D7.
+	// . Empirically writes to regs 0,1 & 2 all de-assert the IRQ (and writes to 3,4..7 don't) (GH#1197)
+	// NB. The same for Mockingboard as there's no automatic handshake from the 6522 (CA2 isn't connected to the SSI263). So a write to reg0, 1 or 2 completes the handshake.
+	if (nReg <= SSI_RATEINF)
 	{
 		CpuIrqDeassert(IS_SPEECH);
 		m_currentMode.D7 = 0;
@@ -205,6 +195,9 @@ void SSI263::Write(BYTE nReg, BYTE nValue)
 #endif
 		if ((m_ctrlArtAmp & CONTROL_MASK) && !(nValue & CONTROL_MASK))	// H->L
 		{
+			// NB. Just changed from CTL=1 (power-down) - where IRQ was de-asserted & D7=0
+			// . So CTL H->L never affects IRQ or D7
+
 			if ((m_durationPhoneme & DURATION_MODE_MASK) != MODE_IRQ_DISABLED)
 			{
 				m_currentMode.function = (m_durationPhoneme & DURATION_MODE_MASK) >> DURATION_MODE_SHIFT;
@@ -214,10 +207,6 @@ void SSI263::Write(BYTE nReg, BYTE nValue)
 			{
 				// "Disables A/!R output only; does not change previous A/!R response" (SSI263 datasheet)
 				m_currentMode.enableInts = 0;
-
-				// TODO: What if IRQ is currently asserted? Does it deassert the IRQ?
-//				CpuIrqDeassert(IS_SPEECH);
-				// NB. D7 is not cleared -- check this
 			}
 
 			// Device out of power down / "standby" mode, so play phoneme
@@ -765,23 +754,23 @@ void SSI263::SetSpeechIRQ(void)
 {
 	if (!m_isVotraxPhoneme)
 	{
-		// Always set SSI263's D7 pin regardless of SSI263 mode (DR1:0), including when SSI263 ints are disabled (via MODE_IRQ_DISABLED)
-		m_currentMode.D7 = 1;	// Set SSI263's D7 pin
-
 		if (m_currentMode.enableInts)
 		{
 			if (m_cardMode == PH_Mockingboard)
 			{
-				if ((GetPCR(m_device) & 1) == 0)		// CA1 Latch/Input = 0 (Negative active edge)
-					UpdateIFR(m_device, 0, SY6522::IxR_SSI263);
-				if (GetPCR(m_device) == 0x0C)			// CA2 Control = b#110 (Low output)
-					m_currentMode.D7 = 0;				// Clear SSI263's D7 pin (cleared by 6522's PCR CA1/CA2 handshake)
-
-				// NB. Don't set CTL=1, as Mockingboard(SMS) speech doesn't work (it sets MODE_IRQ_DISABLED mode during ISR)
-				//pMB->SpeechChip.CtrlArtAmp |= CONTROL_MASK;	// 6522's CA2 sets Power Down mode (pin 18), which sets Control bit
+				if (m_currentMode.D7 == 0)
+				{
+					// 6522's PCR = 0x0C (all SSI263 speech routine use this value, but 0x00 will do equally as well!)
+					// . b3:1 CA2 Control = b#110 (Low output) - not connected
+					// . b0   CA1 Latch/Input = 0 (Negative active edge) - input from SSI263's A/!R
+					if ((GetPCR(m_device) & 1) == 0)		// Level change from SSI263's A/!R, latch this as an interrupt
+						UpdateIFR(m_device, 0, SY6522::IxR_SSI263);
+				}
 			}
-			else if (m_cardMode == PH_Phasor)	// Phasor's SSI263 IRQ (A/!R) line is *also* wired directly to the 6502's IRQ (as well as the 6522's CA1)
+			else if (m_cardMode == PH_Phasor)
 			{
+				// Phasor (in native mode): SSI263 IRQ (A/!R) pin is wired directly to the 6502's IRQ
+				// . And A/!R is wired to the 6522's CA1 but only when in Mockingboard mode
 				CpuIrqAssert(IS_SPEECH);
 			}
 			else
@@ -789,6 +778,9 @@ void SSI263::SetSpeechIRQ(void)
 				_ASSERT(0);
 			}
 		}
+
+		// Always set SSI263's D7 pin regardless of SSI263 mode (DR1:0), including when SSI263 ints are disabled (via MODE_IRQ_DISABLED)
+		m_currentMode.D7 = 1;
 	}
 
 	//