6522via.cpp: Count negative PB6 pulses in T2 counter mode

(nw) VIA interrupt remains disconnected in tv950 due to CRTC-related problems. This is fairly likely to cause regressions in other drivers which may need explicit writes to PB6.

src/devices/machine/6522via.cpp

@@ -7,8 +7,6 @@
     This is based on the M6821 emulation in MAME.
 
     To do:
-
-    T2 pulse counting mode
     Pulse mode handshake output
 
 **********************************************************************/
@@ -139,6 +137,29 @@ uint16_t via6522_device::get_counter1_value()
 	return val;
 }
 
+void via6522_device::counter2_decrement()
+{
+	if (!T2_COUNT_PB6(m_acr))
+		return;
+
+	// count down on T2CL
+	if (m_t2cl-- != 0)
+		return;
+
+	// borrow from T2CH
+	if (m_t2ch-- != 0)
+		return;
+
+	// underflow causes only one interrupt between T2CH writes
+	if (m_t2_active)
+	{
+		m_t2_active = 0;
+
+		LOGINT("T2 INT request ");
+		set_int(INT_T2);
+	}
+}
+
 
 //**************************************************************************
 //  LIVE DEVICE
@@ -170,7 +191,7 @@ via6522_device::via6522_device(const machine_config &mconfig, const char *tag, d
 		m_in_ca1(0),
 		m_in_ca2(0),
 		m_out_ca2(0),
-		m_in_b(0),
+		m_in_b(0xff),
 		m_in_cb1(0),
 		m_in_cb2(0),
 		m_pcr(0),
@@ -283,6 +304,12 @@ void via6522_device::device_reset()
 	m_ca2_handler(m_out_ca2);
 	m_cb1_handler(m_out_cb1);
 	m_cb2_handler(m_out_cb2);
+
+	m_t1->adjust(attotime::never);
+	m_t2->adjust(attotime::never);
+	m_ca2_timer->adjust(attotime::never);
+	m_shift_timer->adjust(attotime::never);
+	m_shift_irq_timer->adjust(attotime::never);
 }
 
 
@@ -487,16 +514,15 @@ void via6522_device::device_timer(emu_timer &timer, device_timer_id id, int para
 
 uint8_t via6522_device::input_pa()
 {
+	uint8_t pa = m_in_a & ~m_ddr_a;
+
 	/// TODO: REMOVE THIS
-	if (!m_in_a_handler.isnull())
+	if (m_ddr_a != 0xff && !m_in_a_handler.isnull())
-	{
+		pa &= m_in_a_handler();
-		if (m_ddr_a != 0xff)
-			m_in_a = m_in_a_handler(0);
 
-		return (m_out_a & m_ddr_a) + (m_in_a & ~m_ddr_a);
+	pa |= m_out_a & m_ddr_a;
-	}
 
-	return m_in_a & (m_out_a | ~m_ddr_a);
+	return pa;
 }
 
 void via6522_device::output_pa()
@@ -507,13 +533,15 @@ void via6522_device::output_pa()
 
 uint8_t via6522_device::input_pb()
 {
+	uint8_t pb = m_in_b & ~m_ddr_b;
+
 	/// TODO: REMOVE THIS
 	if (m_ddr_b != 0xff && !m_in_b_handler.isnull())
 	{
-		m_in_b = m_in_b_handler(0);
+		pb &= m_in_b_handler();
 	}
 
-	uint8_t pb = (m_out_b & m_ddr_b) + (m_in_b & ~m_ddr_b);
+	pb |= m_out_b & m_ddr_b;
 
 	if (T1_SET_PB7(m_acr))
 		pb = (pb & 0x7f) | (m_t1_pb7 << 7);
@@ -538,9 +566,6 @@ void via6522_device::output_pb()
 u8 via6522_device::read(offs_t offset)
 {
 	int val = 0;
-	if (machine().side_effects_disabled())
-		return 0;
-
 	offset &= 0xf;
 
 	switch (offset)
@@ -556,8 +581,11 @@ u8 via6522_device::read(offs_t offset)
 			val = m_latch_b;
 		}
 
+		if (!machine().side_effects_disabled())
+		{
 			LOGINT("PB INT ");
 			CLR_PB_INT();
+		}
 		break;
 
 	case VIA_PA:
@@ -571,6 +599,8 @@ u8 via6522_device::read(offs_t offset)
 			val = m_latch_a;
 		}
 
+		if (!machine().side_effects_disabled())
+		{
 			LOGINT("PA INT ");
 			CLR_PA_INT();
 
@@ -582,6 +612,7 @@ u8 via6522_device::read(offs_t offset)
 
 			if (CA2_PULSE_OUTPUT(m_pcr))
 				m_ca2_timer->adjust(clocks_to_attotime(1));
+		}
 
 		break;
 
@@ -606,8 +637,11 @@ u8 via6522_device::read(offs_t offset)
 		break;
 
 	case VIA_T1CL:
+		if (!machine().side_effects_disabled())
+		{
 			LOGINT("T1CL INT ");
 			clear_int(INT_T1);
+		}
 		val = get_counter1_value() & 0xFF;
 		break;
 
@@ -624,9 +658,12 @@ u8 via6522_device::read(offs_t offset)
 		break;
 
 	case VIA_T2CL:
+		if (!machine().side_effects_disabled())
+		{
 			LOGINT("T2CL INT ");
 			clear_int(INT_T2);
-		if (m_t2_active)
+		}
+		if (m_t2_active && m_t2->enabled())
 		{
 			val = attotime_to_clocks(m_t2->remaining()) & 0xff;
 		}
@@ -644,7 +681,7 @@ u8 via6522_device::read(offs_t offset)
 		break;
 
 	case VIA_T2CH:
-		if (m_t2_active)
+		if (m_t2_active && m_t2->enabled())
 		{
 			val = attotime_to_clocks(m_t2->remaining()) >> 8;
 		}
@@ -664,6 +701,8 @@ u8 via6522_device::read(offs_t offset)
 	case VIA_SR:
 		LOGSHIFT("Read SR: %02x ", m_sr);
 		val = m_sr;
+		if (!machine().side_effects_disabled())
+		{
 			m_out_cb1 = 1;
 			m_cb1_handler(m_out_cb1);
 			m_shift_counter = 0x0f;
@@ -686,6 +725,7 @@ u8 via6522_device::read(offs_t offset)
 				LOGSHIFT("Timer stops");
 			}
 			LOGSHIFT("\n");
+		}
 		break;
 
 	case VIA_PCR:
@@ -839,7 +879,7 @@ void via6522_device::write(offs_t offset, u8 data)
 		}
 		else
 		{
-			m_t2->adjust(clocks_to_attotime(TIMER2_VALUE));
+			//m_t2->adjust(clocks_to_attotime(TIMER2_VALUE));
 			m_t2_active = 1;
 			m_time2 = machine().time();
 		}
@@ -1025,11 +1065,19 @@ void via6522_device::set_pb_line(int line, int state)
 	if (state)
 		m_in_b |= (1 << line);
 	else
+	{
+		if (line == 6 && BIT(m_in_b, 6))
+			counter2_decrement();
+
 		m_in_b &= ~(1 << line);
 	}
+}
 
 WRITE8_MEMBER( via6522_device::write_pb )
 {
+	if (!BIT(data, 6) && BIT(m_in_b, 6))
+		counter2_decrement();
+
 	m_in_b = data;
 }
 

src/devices/machine/6522via.h

@@ -107,6 +107,7 @@ private:
 	static constexpr device_timer_id TIMER_SHIFT_IRQ = 4;
 
 	uint16_t get_counter1_value();
+	void counter2_decrement();
 
 	void set_int(int data);
 	void clear_int(int data);

src/mame/drivers/esprit.cpp

@@ -201,7 +201,7 @@ void esprit_state::esprit3(machine_config &config)
 	crtc.set_char_width(9);
 	crtc.set_update_row_callback(FUNC(esprit_state::crtc_update_row), this);
 	crtc.set_on_update_addr_change_callback(FUNC(esprit_state::crtc_update_addr), this);
-	//crtc.out_hsync_callback().set("via", FUNC(via6522_device::write_pb6)).invert();
+	crtc.out_hsync_callback().set("via", FUNC(via6522_device::write_pb6)).invert();
 }
 
 ROM_START( esprit )