From 7e9c0431c07ea60c1d4c4f3db6a32c42b09e4cd3 Mon Sep 17 00:00:00 2001
From: "R. Belmont" <rb6502@users.noreply.github.com>
Date: Sun, 2 Feb 2014 21:51:50 +0000
Subject: [PATCH] mos6551: support Rockwell 6551s, which show different
 register contents from MOS/CSG parts on reset. [R. Belmont]

---
 src/emu/machine/mos6551.c | 34 +++++++++++++++++++++++++++++++---
 src/emu/machine/mos6551.h | 12 +++++++++++-
 2 files changed, 42 insertions(+), 4 deletions(-)

diff --git a/src/emu/machine/mos6551.c b/src/emu/machine/mos6551.c
index 2aa08bab002..5a6b7c7b618 100644
--- a/src/emu/machine/mos6551.c
+++ b/src/emu/machine/mos6551.c
@@ -67,7 +67,8 @@ mos6551_device::mos6551_device(const machine_config &mconfig, const char *tag, d
 		m_ext_rxc(0),
 		m_cts(1),
 		m_dsr(1),
-		m_dcd(1)
+		m_dcd(1),
+		m_chip_type(MOS6551_TYPE_MOS)
 {
 }
 
@@ -103,7 +104,20 @@ void mos6551_device::device_start()
 void mos6551_device::device_reset()
 {
 	m_ctrl = 0;
-	m_cmd = CMD_RIE;
+
+	switch (m_chip_type)
+	{
+		case MOS6551_TYPE_MOS:
+			m_cmd = CMD_RIE; 
+			break;
+
+		case MOS6551_TYPE_ROCKWELL:
+			m_cmd = 0;
+			break;
+
+		default:
+			fatalerror("mos6551: unknown type %d", m_chip_type);
+	}
 
 	transmit_register_reset();
 	receive_register_reset();
@@ -111,6 +125,16 @@ void mos6551_device::device_reset()
 	update_serial();
 }
 
+//-------------------------------------------------
+//  static_set_type - configuration helper to set
+//  the chip type
+//-------------------------------------------------
+
+void mos6551_device::static_set_type(device_t &device, int type)
+{
+	mos6551_device &mos = downcast<mos6551_device &>(device);
+	mos.m_chip_type = type;
+}
 
 void mos6551_device::device_timer(emu_timer &timer, device_timer_id id, int param, void *ptr)
 {
@@ -321,7 +345,11 @@ WRITE8_MEMBER( mos6551_device::write )
 
 	case 1:
 		// programmed reset
-		m_cmd = (m_cmd & 0xe0) | CMD_RIE;
+		m_cmd = (m_cmd & 0xe0);
+		if (m_chip_type == MOS6551_TYPE_MOS)
+		{
+			m_cmd |= CMD_RIE;
+		}
 		m_st &= ~ST_OR;
 		update_serial();
 		break;
diff --git a/src/emu/machine/mos6551.h b/src/emu/machine/mos6551.h
index 975bcaccb66..078669fcbdd 100644
--- a/src/emu/machine/mos6551.h
+++ b/src/emu/machine/mos6551.h
@@ -33,7 +33,10 @@
 
 #include "emu.h"
 
-
+// MOS 6551s reset with the RIE bit set in the command register
+#define MOS6551_TYPE_MOS		(0)
+// Rockwell (and Synertek) reset with all bits clear in the command register
+#define MOS6551_TYPE_ROCKWELL	(1)
 
 //**************************************************************************
 //  INTERFACE CONFIGURATION MACROS
@@ -51,6 +54,8 @@
 #define MCFG_MOS6551_DTR_HANDLER(_devcb) \
 	devcb = &mos6551_device::set_dtr_handler(*device, DEVCB2_##_devcb);
 
+#define MCFG_MOS6551_TYPE(_type) \
+	mos6551_device::static_set_type(*device, _type);
 
 
 //**************************************************************************
@@ -82,6 +87,9 @@ public:
 
 	void set_rxc(int clock);
 
+	// inline configuration helpers
+	static void static_set_type(device_t &device, int type);
+
 protected:
 	// device-level overrides
 	virtual void device_start();
@@ -181,6 +189,8 @@ protected:
 	int m_dsr;
 	int m_dcd;
 
+	int m_chip_type;
+
 	static const int brg_divider[16];
 };