From 2edee35ac323af4e248b6b034ff0915648f5e5de Mon Sep 17 00:00:00 2001
From: Michael Zapf <github@mizapf.de>
Date: Sun, 5 Jan 2020 17:40:24 +0100
Subject: [PATCH] ti99_2: Removed instability in Load/save to Hexbus floppy.

---
 src/devices/bus/hexbus/hexbus.cpp          |  9 +++++++++
 src/devices/bus/hexbus/hexbus.h            |  3 +++
 src/devices/bus/ti99/internal/992board.cpp | 19 +++++++++++++------
 src/devices/bus/ti99/internal/992board.h   |  5 +++--
 4 files changed, 28 insertions(+), 8 deletions(-)

diff --git a/src/devices/bus/hexbus/hexbus.cpp b/src/devices/bus/hexbus/hexbus.cpp
index 5fec624ab39..0b8d7821cb6 100644
--- a/src/devices/bus/hexbus/hexbus.cpp
+++ b/src/devices/bus/hexbus/hexbus.cpp
@@ -415,6 +415,15 @@ uint8_t hexbus_chained_device::to_line_state(uint8_t data, bool bav, bool hsk)
 	return lines;
 }
 
+/*
+    Convenience function to get a data bit.
+*/
+int hexbus_chained_device::data_bit(int n)
+{
+	const uint8_t testbit[4] = { 0x01, 0x02, 0x40, 0x80 };
+	return (m_current_bus_value & testbit[n&3])? 1:0;
+}
+
 // ------------------------------------------------------------------------
 
 }   }   // end namespace bus::hexbus
diff --git a/src/devices/bus/hexbus/hexbus.h b/src/devices/bus/hexbus/hexbus.h
index 7ff730e94a7..76092c0f16f 100644
--- a/src/devices/bus/hexbus/hexbus.h
+++ b/src/devices/bus/hexbus/hexbus.h
@@ -127,6 +127,9 @@ protected:
 
 	// Data lines
 	static int data_lines(uint8_t lines) { return (((lines & 0xc0) >> 4) | (lines & 0x03)); }
+
+	// Return the selected data bit (0-3)
+	int data_bit(int n);
 };
 
 // ------------------------------------------------------------------------
diff --git a/src/devices/bus/ti99/internal/992board.cpp b/src/devices/bus/ti99/internal/992board.cpp
index ba5aa9c2f58..fcb5d904a68 100644
--- a/src/devices/bus/ti99/internal/992board.cpp
+++ b/src/devices/bus/ti99/internal/992board.cpp
@@ -355,7 +355,8 @@ io992_device::io992_device(const machine_config &mconfig, device_type type, cons
 		m_videoctrl(*this, "^" TI992_VDC_TAG),
 		m_keyboard(*this, "LINE%u", 0U),
 		m_set_rom_bank(*this),
-		m_key_row(0)
+		m_key_row(0),
+		m_hsk_released(true)
 {
 }
 
@@ -473,14 +474,16 @@ uint8_t io992_device::cruread(offs_t offset)
 	case 0xe802:
 	case 0xe804:
 	case 0xe806:
+		return data_bit(offset&3);
 	case 0xe808:
+		return (bus_hsk_level()==ASSERT_LINE)? 0:1;
 	case 0xe80a:
-		return ((m_current_bus_value & m_hexbval[offset&7])==0)? 0:1;
+		return (bus_bav_level()==ASSERT_LINE)? 0:1;
 
 	case 0xe80c:
 		// e80c (bit 6) seems to indicate that the HSK* line has been released
-		// own HSK*=1 and HSK*=0 on the bus
-		return ((own_hsk_level()==CLEAR_LINE) && (bus_hsk_level()==ASSERT_LINE))? 0:1;
+		// and is now asserted again
+		return (m_hsk_released && (bus_hsk_level()==ASSERT_LINE))? 1:0;
 
 	case 0xe80e:
 		inp = m_cassette->input();
@@ -499,8 +502,6 @@ void io992_device::cruwrite(offs_t offset, uint8_t data)
 
 	LOGMASKED(LOG_CRU, "CRU %04x <- %1x\n", address, data);
 
-//  uint8_t olddata = m_latch_out;
-
 	switch (address)
 	{
 	// Select the current keyboard row. Also, bit 0 is used to switch the
@@ -544,6 +545,7 @@ void io992_device::cruwrite(offs_t offset, uint8_t data)
 
 	case 0xe808:  // HSK
 		set_hsk_line(data!=0? CLEAR_LINE : ASSERT_LINE);
+		m_hsk_released = (bus_hsk_level()==CLEAR_LINE);
 		break;
 
 	case 0xe80c:
@@ -581,6 +583,11 @@ void io992_device::hexbus_value_changed(uint8_t data)
 			LOGMASKED(LOG_HEXBUS, "Latching HSK*; got data %01x\n", (data>>4)|(data&3));
 			latch_hsk();
 		}
+		else
+		{
+			LOGMASKED(LOG_HEXBUS, "HSK* released\n");
+			m_hsk_released = true;
+		}
 	}
 	else
 		LOGMASKED(LOG_HEXBUS, "Ignoring Hexbus change (to %02x), BAV*=%d\n", data, (own_bav_level()==ASSERT_LINE)? 0:1);
diff --git a/src/devices/bus/ti99/internal/992board.h b/src/devices/bus/ti99/internal/992board.h
index 49649bed3e3..3b27462b323 100644
--- a/src/devices/bus/ti99/internal/992board.h
+++ b/src/devices/bus/ti99/internal/992board.h
@@ -116,8 +116,6 @@ protected:
 	void hexbus_value_changed(uint8_t data) override;
 
 private:
-	const uint8_t m_hexbval[6] = { 0x01, 0x02, 0x40, 0x80, 0x10, 0x04 };
-
 	required_device<hexbus::hexbus_device> m_hexbus;
 	required_device<cassette_image_device> m_cassette;
 	required_device<video992_device> m_videoctrl;
@@ -128,6 +126,9 @@ private:
 
 	// Keyboard row
 	int m_key_row;
+
+	// HSK* released flag. This is queried as CRU bit 6 (with the current HSK* level).
+	bool m_hsk_released;
 };