kb3600: track "down" keys to avoid spurious retriggers during fast typing (nw)

src/mess/machine/kb3600.c

@@ -89,6 +89,7 @@ void ay3600_device::device_start()
 	// state saving
 	save_item(NAME(m_b));
 	save_item(NAME(m_ako));
+	save_item(NAME(m_keys_down));
 }
 
 
@@ -99,6 +100,10 @@ void ay3600_device::device_start()
 void ay3600_device::device_reset()
 {
 	m_ako = 0;
+	for (int i = 0; i < MAX_KEYS_DOWN; i++)
+	{
+		m_keys_down[i] = -1;
+	}
 }
 
 //-------------------------------------------------
@@ -128,27 +133,62 @@ void ay3600_device::device_timer(emu_timer &timer, device_timer_id id, int param
 
 		for (int y = 0; y < 10; y++)
 		{
+			int b = (x * 10) + y;
+
+			if (b > 63)
+			{
+				b -= 64;
+				b = 0x100 | b;
+			}
+
+			b |= (m_read_shift() << 6);
+			b |= (m_read_control() << 7);
+
 			if (BIT(data, y))
 			{
-				int b = (x * 10) + y;
+				bool found = false;
 
-				ako = 1;
+				// is this key already down?
-
+				for (int k = 0; k < MAX_KEYS_DOWN; k++)
-				if (b > 63)
 				{
-					b -= 64;
+					if (b == m_keys_down[k])
-					b = 0x100 | b;
+					{
+						found = true;
+						break;
+					}
 				}
 
-				b |= (m_read_shift() << 6);
+				if (!found)
-				b |= (m_read_control() << 7);
-
-				if (m_b != b)
 				{
-					m_b = b;
+					ako = 1; 
 
-					m_write_data_ready(1);
+					if (m_b != b)
-					return;
+					{
+						m_b = b;
+
+						m_write_data_ready(1);
+						return;
+					}
+
+					// add to the keys down list
+					for (int k = 0; k < MAX_KEYS_DOWN; k++)
+					{
+						if (m_keys_down[k] == -1)
+						{
+							m_keys_down[k] = b;
+							break;
+						}
+					}
+				}
+			}
+			else	// key released, unmark it from the keys_down table
+			{
+				for (int k = 0; k < MAX_KEYS_DOWN; k++)
+				{
+					if (b == m_keys_down[k])
+					{
+						m_keys_down[k] = -1;
+					}
 				}
 			}
 		}

src/mess/machine/kb3600.h

@@ -132,9 +132,13 @@ protected:
 	virtual void device_timer(emu_timer &timer, device_timer_id id, int param, void *ptr);
 
 private:
+	static const int MAX_KEYS_DOWN = 4;
+
 	int m_b;                    // output buffer
 	int m_ako;                  // any key down
 
+	int m_keys_down[MAX_KEYS_DOWN];
+
 	// timers
 	emu_timer *m_scan_timer;    // keyboard scan timer
 };