From 1296414948623ffcffe01d2409fca6b927707131 Mon Sep 17 00:00:00 2001
From: Vas Crabb <vas@vastheman.com>
Date: Sun, 29 Jan 2017 21:14:23 +1100
Subject: [PATCH] dec0.cpp latch cleanup: 'LS374 sensed positive edge others
 are educted guesses

---
 src/mame/includes/dec0.h  |  4 +--
 src/mame/machine/dec0.cpp | 62 ++++++++++++++++++++++-----------------
 2 files changed, 37 insertions(+), 29 deletions(-)

diff --git a/src/mame/includes/dec0.h b/src/mame/includes/dec0.h
index b75982e295f..415ccb58174 100644
--- a/src/mame/includes/dec0.h
+++ b/src/mame/includes/dec0.h
@@ -54,8 +54,8 @@ public:
 	optional_shared_ptr<uint8_t> m_hippodrm_shared_ram;
 
 	mcu_type m_game;
-	int m_i8751_return;
-	int m_i8751_command;
+	uint16_t m_i8751_return;
+	uint16_t m_i8751_command;
 	int m_slyspy_state;
 	int m_hippodrm_msb;
 	int m_hippodrm_lsb;
diff --git a/src/mame/machine/dec0.cpp b/src/mame/machine/dec0.cpp
index 3e10ff56c18..4aef1d1dcff 100644
--- a/src/mame/machine/dec0.cpp
+++ b/src/mame/machine/dec0.cpp
@@ -10,7 +10,9 @@ Data East machine functions - Bryan McPhail, mish@tendril.co.uk
 
 #include "emu.h"
 #include "includes/dec0.h"
+
 #include "cpu/h6280/h6280.h"
+#include "cpu/m68000/m68000.h"
 #include "cpu/mcs51/mcs51.h"
 
 
@@ -165,39 +167,35 @@ WRITE16_MEMBER(dec0_state::hippodrm_68000_share_w)
 
 READ8_MEMBER(dec0_state::dec0_mcu_port_r)
 {
-	int latchEnable=m_i8751_ports[2]>>4;
+	uint8_t result = 0xff;
 
-	// P0 connected to 4 latches
-	if (offset==0)
+	// P0 connected to latches
+	if (offset == 0)
 	{
-		if ((latchEnable&1)==0)
-			return m_i8751_command>>8;
-		else if ((latchEnable&2)==0)
-			return m_i8751_command&0xff;
-		else if ((latchEnable&4)==0)
-			return m_i8751_return>>8;
-		else if ((latchEnable&8)==0)
-			return m_i8751_return&0xff;
+		if (!BIT(m_i8751_ports[2], 4))
+			result &= m_i8751_command >> 8;
+		if (!BIT(m_i8751_ports[2], 5))
+			result &= m_i8751_command & 0x00ff;
 	}
 
-	return 0xff;
+	return result;
 }
 
 WRITE8_MEMBER(dec0_state::dec0_mcu_port_w)
 {
-	m_i8751_ports[offset]=data;
-
-	if (offset==2)
+	if (offset == 2)
 	{
-		if ((data&0x4)==0)
-			m_maincpu->set_input_line(5, HOLD_LINE);
-		if ((data&0x8)==0)
+		if (!BIT(data, 2) && BIT(m_i8751_ports[2], 2))
+			m_maincpu->set_input_line(M68K_IRQ_5, HOLD_LINE);
+		if (!BIT(data, 3))
 			m_mcu->set_input_line(MCS51_INT1_LINE, CLEAR_LINE);
-		if ((data&0x40)==0)
-			m_i8751_return=(m_i8751_return&0xff00)|(m_i8751_ports[0]);
-		if ((data&0x80)==0)
-			m_i8751_return=(m_i8751_return&0xff)|(m_i8751_ports[0]<<8);
+		if (BIT(data, 6) && !BIT(m_i8751_ports[2], 6))
+			m_i8751_return = (m_i8751_return & 0xff00) | m_i8751_ports[0];
+		if (BIT(data, 7) && !BIT(m_i8751_ports[2], 7))
+			m_i8751_return = (m_i8751_return & 0x00ff) | (m_i8751_ports[0] << 8);
 	}
+
+	m_i8751_ports[offset] = data;
 }
 
 void dec0_state::baddudes_i8751_write(int data)
@@ -300,12 +298,22 @@ void dec0_state::birdtry_i8751_write(int data)
 
 void dec0_state::dec0_i8751_write(int data)
 {
-	m_i8751_command=data;
+	m_i8751_command = data;
 
-	/* Writes to this address cause an IRQ to the i8751 microcontroller */
-	if (m_game == mcu_type::EMULATED)     m_mcu->set_input_line(MCS51_INT1_LINE, ASSERT_LINE);
-	if (m_game == mcu_type::BADDUDES_SIM) baddudes_i8751_write(data);
-	if (m_game == mcu_type::BIRDTRY_SIM)  birdtry_i8751_write(data);
+	/* Writes to this address raise an IRQ on the i8751 microcontroller */
+	switch (m_game)
+	{
+	case mcu_type::EMULATED:
+		if (BIT(m_i8751_ports[2], 3))
+			m_mcu->set_input_line(MCS51_INT1_LINE, ASSERT_LINE);
+		break;
+	case mcu_type::BADDUDES_SIM:
+		baddudes_i8751_write(data);
+		break;
+	case mcu_type::BIRDTRY_SIM:
+		birdtry_i8751_write(data);
+		break;
+	}
 
 	//logerror("%s: warning - write %02x to i8751\n",machine().describe_context(),data);
 }