From 0e4b21121fdcd763a7b3d4ff015ca1dab4bd0d8f Mon Sep 17 00:00:00 2001
From: angelosa <lordkale4@gmail.com>
Date: Sat, 28 Oct 2023 20:09:00 +0200
Subject: nec/pc9801.cpp: implement DMA r/w 1MB mask

---
 src/mame/nec/pc9801.cpp | 57 +++++++++++++++++++++++++++++++++++++++++++++++++
 src/mame/nec/pc9801.h   |  9 ++++++--
 src/mame/nec/pc_h98.cpp | 21 ++++++++++++++++--
 3 files changed, 83 insertions(+), 4 deletions(-)

diff --git a/src/mame/nec/pc9801.cpp b/src/mame/nec/pc9801.cpp
index c9d61f1e60f..5c8777e23c2 100644
--- a/src/mame/nec/pc9801.cpp
+++ b/src/mame/nec/pc9801.cpp
@@ -1538,6 +1538,63 @@ void pc9801_state::dma_write_byte(offs_t offset, uint8_t data)
 	program.write_byte(addr, data);
 }
 
+uint8_t pc9801vm_state::dma_read_byte(offs_t offset)
+{
+	address_space &program = m_maincpu->space(AS_PROGRAM);
+	offs_t addr = (m_dma_offset[m_dack] << 16) | offset;
+
+	if (BIT(m_dma_access_ctrl, 2))
+		addr &= 0xfffff;
+
+	if(offset == 0xffff)
+	{
+		switch(m_dma_autoinc[m_dack])
+		{
+			case 1:
+			{
+				uint8_t page = m_dma_offset[m_dack];
+				m_dma_offset[m_dack] = ((page + 1) & 0xf) | (page & 0xf0);
+				break;
+			}
+			case 3:
+				m_dma_offset[m_dack]++;
+				break;
+		}
+	}
+
+//  logerror("%08x %02x\n",addr, m_dma_access_ctrl);
+	return program.read_byte(addr);
+}
+
+
+void pc9801vm_state::dma_write_byte(offs_t offset, uint8_t data)
+{
+	address_space &program = m_maincpu->space(AS_PROGRAM);
+	offs_t addr = (m_dma_offset[m_dack] << 16) | offset;
+
+	if (BIT(m_dma_access_ctrl, 2))
+		addr &= 0xfffff;
+
+	if(offset == 0xffff)
+	{
+		switch(m_dma_autoinc[m_dack])
+		{
+			case 1:
+			{
+				uint8_t page = m_dma_offset[m_dack];
+				m_dma_offset[m_dack] = ((page + 1) & 0xf) | (page & 0xf0);
+				break;
+			}
+			case 3:
+				m_dma_offset[m_dack]++;
+				break;
+		}
+	}
+//  logerror("%08x %02x %02x\n",addr,data, m_dma_access_ctrl);
+
+	program.write_byte(addr, data);
+}
+
 void pc9801_state::set_dma_channel(int channel, int state)
 {
 	if (!state) m_dack = channel;
diff --git a/src/mame/nec/pc9801.h b/src/mame/nec/pc9801.h
index dff6f5076d3..6b19b313c42 100644
--- a/src/mame/nec/pc9801.h
+++ b/src/mame/nec/pc9801.h
@@ -259,6 +259,9 @@ protected:
 	uint8_t m_dma_autoinc[4];
 	int m_dack;
 
+	virtual uint8_t dma_read_byte(offs_t offset);
+	virtual void dma_write_byte(offs_t offset, uint8_t data);
+
 private:
 	void dmapg4_w(offs_t offset, uint8_t data);
 
@@ -266,8 +269,7 @@ private:
 
 	void dma_hrq_changed(int state);
 	void tc_w(int state);
-	uint8_t dma_read_byte(offs_t offset);
-	void dma_write_byte(offs_t offset, uint8_t data);
+
 	void dack0_w(int state);
 	void dack1_w(int state);
 	void dack2_w(int state);
@@ -423,6 +425,9 @@ protected:
 	u8 m_dma_access_ctrl = 0;
 	u8 m_ide_sel = 0;
 
+	virtual uint8_t dma_read_byte(offs_t offset) override;
+	virtual void dma_write_byte(offs_t offset, uint8_t data) override;
+
 	// starting from PC9801VF/U buzzer is substituted with a DAC1BIT
 	bool m_dac1bit_disable;
 
diff --git a/src/mame/nec/pc_h98.cpp b/src/mame/nec/pc_h98.cpp
index 76f3267e60a..fac32fdcd26 100644
--- a/src/mame/nec/pc_h98.cpp
+++ b/src/mame/nec/pc_h98.cpp
@@ -21,6 +21,10 @@ public:
 	{}
 
 	void pc_h98s(machine_config &config);
+
+protected:
+	DECLARE_MACHINE_START(pc_h98);
+	DECLARE_MACHINE_RESET(pc_h98);
 };
 
 // TODO: backported from pc9801_epson.cpp, needs mods
@@ -123,6 +127,19 @@ static INPUT_PORTS_START( pc_h98 )
 	PORT_CONFSETTING(    0x04, DEF_STR( No ) )
 INPUT_PORTS_END
 
+MACHINE_START_MEMBER(pc_hyper98_state,pc_h98)
+{
+	MACHINE_START_CALL_MEMBER(pc9801bx2);
+}
+
+MACHINE_RESET_MEMBER(pc_hyper98_state,pc_h98)
+{
+	MACHINE_RESET_CALL_MEMBER(pc9801bx2);
+
+	// boots with DMA > 1MB on.
+	m_dma_access_ctrl = 0xfb;
+}
+
 void pc_hyper98_state::pc_h98s(machine_config &config)
 {
 	pc9801bx2(config);
@@ -132,8 +149,8 @@ void pc_hyper98_state::pc_h98s(machine_config &config)
 	m_maincpu->set_addrmap(AS_IO, &pc_hyper98_state::pc9801bx2_io);
 	m_maincpu->set_irq_acknowledge_callback("pic8259_master", FUNC(pic8259_device::inta_cb));
 
-	MCFG_MACHINE_START_OVERRIDE(pc_hyper98_state, pc9801bx2)
-	MCFG_MACHINE_RESET_OVERRIDE(pc_hyper98_state, pc9801bx2)
+	MCFG_MACHINE_START_OVERRIDE(pc_hyper98_state, pc_h98)
+	MCFG_MACHINE_RESET_OVERRIDE(pc_hyper98_state, pc_h98)
 
 	m_ram->set_default_size("14M");
 	// TODO: extra options, 1.6MB up to 45.6MB
-- 
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