es5506.cpp fixes: [Christian Brunschen]

- Fixed readback of global registers when the current page was in a certain range
- Real h/w does run the voice for a zero-length loop and the synths rely on it

These changes fix the playback of "Transwaves" on the VFX and SD-series synths.

src/devices/sound/es5506.cpp

@@ -1096,9 +1096,15 @@ void es5505_device::generate_samples(INT32 **outputs, int offset, int samples)
 		es550x_voice *voice = &m_voice[v];
 		UINT16 *base = m_region_base[voice->control >> 14];
 
+// This special case does not appear to match the behaviour observed in the es5505 in
+// actual Ensoniq synthesizers: those, it turns out, do set loop start and end to the
+// same value, and expect the voice to keep running. Examples can be found among the
+// transwaves on the VFX / SD-1 series of synthesizers.
+#if 0
 		/* special case: if end == start, stop the voice */
 		if (voice->start == voice->end)
 			voice->control |= CONTROL_STOP0;
+#endif
 
 		int voice_channel = (voice->control & CONTROL_CAMASK) >> 10;
 		int channel = voice_channel % m_channels;
@@ -2165,6 +2171,16 @@ inline UINT16 es5505_device::reg_read_test(es550x_voice *voice, offs_t offset)
 				result = m_read_port_cb(0);
 			break;
 
+		/* The following are global, and thus accessible form all pages */
+		case 0x0d:  /* ACT */
+			result = m_active_voices;
+			break;
+
+		case 0x0e:  /* IRQV */
+			result = m_irqv;
+			update_internal_irq_state();
+			break;
+
 		case 0x0f:  /* PAGE */
 			result = m_current_page;
 			break;

src/mame/drivers/esq5505.cpp

@@ -100,7 +100,7 @@
     62 = DATA INCREMENT
     63 = DATA DECREMENT
 
-    VFX / VFX-SD / SD-1 analog values:
+    VFX / VFX-SD / SD-1 analog values: all values are 10 bits, left-justified within 16 bits.
     0 = Pitch Bend
     1 = Patch Select
     2 = Mod Wheel
@@ -243,28 +243,17 @@ SLOT_INTERFACE_END
 
 IRQ_CALLBACK_MEMBER(esq5505_state::maincpu_irq_acknowledge_callback)
 {
-	// We immediately update the interrupt presented to the CPU, so that it doesn't
-	// end up retrying the same interrupt over and over. We then return the appropriate vector.
-	int vector = 0;
 	switch(irqline) {
 	case 1:
-		otis_irq_state = 0;
-		vector = M68K_INT_ACK_AUTOVECTOR;
-		break;
+		return M68K_INT_ACK_AUTOVECTOR;
 	case 2:
-		dmac_irq_state = 0;
-		vector = dmac_irq_vector;
-		break;
+		return dmac_irq_vector;
 	case 3:
-		duart_irq_state = 0;
-		vector = duart_irq_vector;
-		break;
+		return duart_irq_vector;
 	default:
 		logerror("\nUnexpected IRQ ACK Callback: IRQ %d\n", irqline);
 		return 0;
 	}
-	update_irq_to_maincpu();
-	return vector;
 }
 
 void esq5505_state::machine_start()
@@ -283,13 +272,13 @@ void esq5505_state::machine_reset()
 	floppy_connector *con = machine().device<floppy_connector>("wd1772:0");
 	floppy_image_device *floppy = con ? con->get_device() : nullptr;
 
-	// Default analog values:
-	m_analog_values[0] = 0x7fff; // pitch mod: start in the center
+	// Default analog values: all values are 10 bits, left-justified within 16 bits.
+	m_analog_values[0] = 0x7fc0; // pitch mod: start in the center
 	m_analog_values[1] = 0x0000; // patch select: nothing pressed.
-	m_analog_values[2] = 0x0000; // mod wheel: at the bottom, no modulation
-	m_analog_values[3] = 0xcccc; // data entry: somewhere in the middle
-	m_analog_values[4] = 0xffff; // control voltage / pedal: full on.
-	m_analog_values[5] = 0xffff; // Volume control: full on.
+	m_analog_values[2] = 0xffc0; // mod wheel: at the bottom, no modulation
+	m_analog_values[3] = 0xccc0; // data entry: somewhere in the middle
+	m_analog_values[4] = 0xffc0; // control voltage / pedal: full on.
+	m_analog_values[5] = 0xffc0; // Volume control: full on.
 	m_analog_values[6] = 0x7fc0; // Battery voltage: something reasonable.
 	m_analog_values[7] = 0x5540; // vRef to check battery.
 
@@ -316,7 +305,7 @@ void esq5505_state::machine_reset()
 }
 
 void esq5505_state::update_irq_to_maincpu() {
-	//printf("\nupdating IRQ state: have OTIS=%d, DMAC=%d, DUART=%d\n", otis_irq_state, dmac_irq_state, duart_irq_state);
+	// printf("updating IRQ state: have OTIS=%d, DMAC=%d, DUART=%d\n", otis_irq_state, dmac_irq_state, duart_irq_state);
 	if (duart_irq_state) {
 		m_maincpu->set_input_line(M68K_IRQ_2, CLEAR_LINE);
 		m_maincpu->set_input_line(M68K_IRQ_1, CLEAR_LINE);
@@ -526,6 +515,7 @@ WRITE8_MEMBER(esq5505_state::dma_end)
 		dmac_irq_state = 0;
 	}
 
+	// printf("IRQ update from DMAC: have OTIS=%d, DMAC=%d, DUART=%d\n", otis_irq_state, dmac_irq_state, duart_irq_state);
 	update_irq_to_maincpu();
 }
 
@@ -977,7 +967,9 @@ DRIVER_INIT_MEMBER(esq5505_state,sq1)
 {
 	DRIVER_INIT_CALL(common);
 	m_system_type = SQ1;
+#if KEYBOARD_HACK
 	shift = 60;
+#endif
 }
 
 DRIVER_INIT_MEMBER(esq5505_state,denib)