a800: Add support for the ICD R-Time 8 cartridge

scripts/src/bus.lua

@@ -53,6 +53,8 @@ if (BUSES["A800"]~=null) then
 		MAME_DIR .. "src/devices/bus/a800/rom.h",
 		MAME_DIR .. "src/devices/bus/a800/oss.cpp",
 		MAME_DIR .. "src/devices/bus/a800/oss.h",
+		MAME_DIR .. "src/devices/bus/a800/rtime8.cpp",
+		MAME_DIR .. "src/devices/bus/a800/rtime8.h",
 		MAME_DIR .. "src/devices/bus/a800/sparta.cpp",
 		MAME_DIR .. "src/devices/bus/a800/sparta.h",
 	}

src/devices/bus/a800/a800_carts.h

@@ -7,6 +7,7 @@
 
 
 #include "rom.h"
+#include "rtime8.h"
 #include "oss.h"
 #include "sparta.h"
 
@@ -31,6 +32,7 @@ static void a800_left(device_slot_interface &device)
 	device.option_add_internal("a800_tlink2",   A800_ROM_TELELINK2);
 	device.option_add_internal("a800_sitsa",    A800_ROM_MICROCALC);
 	device.option_add_internal("a800_corina",   A800_ROM);  // NOT SUPPORTED YET!
+	device.option_add(         "rtime8",        A800_RTIME8); // not a ROM cartridge
 	device.option_add_internal("xegs",          XEGS_ROM);
 }
 

src/devices/bus/a800/rtime8.cpp

@@ -0,0 +1,70 @@
+// license:BSD-3-Clause
+// copyright-holders:AJR
+/***********************************************************************************************************
+
+    ICD R-Time 8 (Atari 800 cartridge)
+
+    The circuitry in this clock cartridge is very simple, containing the RTC itself, oscillator and
+    battery, and a 74HCT138 to decode the $D5B8-$D5BF address range from the /CCTL and A7-A3 pins. No ROM
+    is included; however, the cartridge can be placed in the (currently unemulated) passthrough slot of the
+    SpartaDOS X cartridge.
+
+***********************************************************************************************************/
+
+#include "emu.h"
+#include "rtime8.h"
+
+// device type definition
+DEFINE_DEVICE_TYPE(A800_RTIME8, a800_rtime8_device, "a800_rtime8", "ICD R-Time 8")
+
+
+//-------------------------------------------------
+//  a800_rtime8_device - constructor
+//-------------------------------------------------
+
+a800_rtime8_device::a800_rtime8_device(const machine_config &mconfig, const char *tag, device_t *owner, u32 clock)
+	: device_t(mconfig, A800_RTIME8, tag, owner, clock)
+	, device_a800_cart_interface(mconfig, *this) 
+	, m_rtc(*this, "rtc")
+{
+}
+
+//-------------------------------------------------
+//  device_add_mconfig - configure subdevices
+//-------------------------------------------------
+
+void a800_rtime8_device::device_add_mconfig(machine_config &config)
+{
+	M3002(config, m_rtc, 32.768_kHz_XTAL);
+}
+
+//-------------------------------------------------
+//  device_start - device-specific startup
+//-------------------------------------------------
+
+void a800_rtime8_device::device_start()
+{
+}
+
+
+//-------------------------------------------------
+//  read_d5xx - handle reads from $D500-$D5FF
+//-------------------------------------------------
+
+u8 a800_rtime8_device::read_d5xx(offs_t offset)
+{
+	if ((offset & 0xf8) == 0xb8)
+		return m_rtc->read(); // TODO: D7-D4 is open bus, in case this matters
+	else
+		return 0xff;
+}
+
+//-------------------------------------------------
+//  write_d5xx - handle writes to $D500-$D5FF
+//-------------------------------------------------
+
+void a800_rtime8_device::write_d5xx(offs_t offset, u8 data)
+{
+	if ((offset & 0xf8) == 0xb8)
+		m_rtc->write(data & 0x0f);
+}

src/devices/bus/a800/rtime8.h

@@ -0,0 +1,37 @@
+// license:BSD-3-Clause
+// copyright-holders:AJR
+
+#ifndef MAME_BUS_A800_RTIME8_H
+#define MAME_BUS_A800_RTIME8_H
+
+#pragma once
+
+#include "a800_slot.h"
+#include "machine/m3002.h"
+
+
+// ======================> a800_rtime8_device
+
+class a800_rtime8_device : public device_t, public device_a800_cart_interface
+{
+public:
+	// construction/destruction
+	a800_rtime8_device(const machine_config &mconfig, const char *tag, device_t *owner, u32 clock);
+
+protected:
+	// device-level overrides
+	virtual void device_add_mconfig(machine_config &config) override;
+	virtual void device_start() override;
+
+	// device_a800_cart_interface overrides
+	virtual u8 read_d5xx(offs_t offset) override;
+	virtual void write_d5xx(offs_t offset, u8 data) override;
+
+private:
+	required_device<m3002_device> m_rtc;
+};
+
+// device type declaration
+DECLARE_DEVICE_TYPE(A800_RTIME8, a800_rtime8_device)
+
+#endif // MAME_BUS_A800_RTIME8_H

src/mame/atari/atari400.cpp

@@ -1919,6 +1919,7 @@ void a400_state::setup_cart(a800_cart_slot_device *slot)
 	m_cart_disabled = 0;
 	m_last_offs = -1;
 
+	// FIXME: this driver should not have to differentiate between cartridge types
 	if (slot->exists())
 	{
 		switch (slot->get_cart_type())
@@ -2002,6 +2003,13 @@ void a400_state::setup_cart(a800_cart_slot_device *slot)
 			break;
 		}
 	}
+	else if (slot->get_card_device() != nullptr)
+	{
+		m_maincpu->space(AS_PROGRAM).install_read_handler(0x8000, 0xbfff, read8sm_delegate(*slot, FUNC(a800_cart_slot_device::read_80xx)));
+		m_maincpu->space(AS_PROGRAM).install_write_handler(0x8000, 0xbfff, write8sm_delegate(*slot, FUNC(a800_cart_slot_device::write_80xx)));
+		m_maincpu->space(AS_PROGRAM).install_read_handler(0xd500, 0xd5ff, read8sm_delegate(*slot, FUNC(a800_cart_slot_device::read_d5xx)));
+		m_maincpu->space(AS_PROGRAM).install_write_handler(0xd500, 0xd5ff, write8sm_delegate(*slot, FUNC(a800_cart_slot_device::write_d5xx)));
+	}
 }