bus/bbc/internal: Added the Memex-B20 board.

scripts/src/bus.lua

@@ -551,6 +551,8 @@ if (BUSES["BBC_INTERNAL"]~=null) then
 		MAME_DIR .. "src/devices/bus/bbc/internal/cumana68k.h",
 		MAME_DIR .. "src/devices/bus/bbc/internal/integrab.cpp",
 		MAME_DIR .. "src/devices/bus/bbc/internal/integrab.h",
+		MAME_DIR .. "src/devices/bus/bbc/internal/memex.cpp",
+		MAME_DIR .. "src/devices/bus/bbc/internal/memex.h",
 		MAME_DIR .. "src/devices/bus/bbc/internal/morleyaa.cpp",
 		MAME_DIR .. "src/devices/bus/bbc/internal/morleyaa.h",
 		MAME_DIR .. "src/devices/bus/bbc/internal/overlay.cpp",

src/devices/bus/bbc/internal/internal.cpp

@@ -162,6 +162,7 @@ WRITE_LINE_MEMBER(bbc_internal_slot_device::irq6502_w)
 #include "atpl.h"
 #include "cumana68k.h"
 #include "integrab.h"
+#include "memex.h"
 #include "morleyaa.h"
 #include "overlay.h"
 #include "peartree.h"
@@ -186,6 +187,7 @@ void bbcb_internal_devices(device_slot_interface &device)
 	device.option_add("atplsw", BBC_ATPLSW);            /* ATPL Sidewise ROM/RAM expansion */
 	device.option_add("cumana68k", BBC_CUMANA68K);      /* Cumana 68008 Upgrade Board */
 	device.option_add("integrab", BBC_INTEGRAB);        /* Computech Integra-B */
+	device.option_add("memexb20", BBC_MEMEXB20);        /* Memex-B20 RAM expansion */
 	device.option_add("mr3000", BBC_MR3000);            /* Peartree MR3000 ROM board */
 	device.option_add("mr4200", BBC_MR4200);            /* Peartree MR4200 RAM board */
 	device.option_add("mr4300", BBC_MR4300);            /* Peartree MR4300 ROM/RAM board */

src/devices/bus/bbc/internal/memex.cpp

@@ -0,0 +1,109 @@
+// license:BSD-3-Clause
+// copyright-holders:Nigel Barnes
+/**********************************************************************
+
+    Memex B20 20K RAM expansion
+
+    This is a DIY project from the May 1984 issue of Electronics and
+    Computing, with part two of the project in the August 1984 issue.
+
+**********************************************************************/
+
+
+#include "emu.h"
+#include "memex.h"
+
+
+//**************************************************************************
+//  DEVICE DEFINITIONS
+//**************************************************************************
+
+DEFINE_DEVICE_TYPE(BBC_MEMEXB20, bbc_memexb20_device, "bbc_memexb20", "Memex-B20 RAM expansion");
+
+
+//-------------------------------------------------
+//  ROM( memexb20 )
+//-------------------------------------------------
+
+ROM_START(memexb20)
+	ROM_REGION(0x2000, "exp_rom", 0)
+	ROM_LOAD("memex-b20_v2.2.rom", 0x0000, 0x2000, CRC(98ee8eb6) SHA1(aad311797e204b0b69450460f8b4605409c31ddd))
+ROM_END
+
+//-------------------------------------------------
+//  rom_region - device-specific ROM region
+//-------------------------------------------------
+
+const tiny_rom_entry *bbc_memexb20_device::device_rom_region() const
+{
+	return ROM_NAME(memexb20);
+}
+
+
+//**************************************************************************
+//  LIVE DEVICE
+//**************************************************************************
+
+//-------------------------------------------------
+//  bbc_memexb20_device - constructor
+//-------------------------------------------------
+
+bbc_memexb20_device::bbc_memexb20_device(const machine_config &mconfig, const char *tag, device_t *owner, uint32_t clock)
+	: device_t(mconfig, BBC_MEMEXB20, tag, owner, clock)
+	, device_bbc_internal_interface(mconfig, *this)
+	, m_shadow(false)
+{
+}
+
+//-------------------------------------------------
+//  device_start - device-specific startup
+//-------------------------------------------------
+
+void bbc_memexb20_device::device_start()
+{
+	address_space &program = m_maincpu->space(AS_PROGRAM);
+
+	program.install_write_handler(0xd000, 0xd000, write8smo_delegate(*this, FUNC(bbc_memexb20_device::enable_w)));
+	program.install_write_handler(0xc000, 0xc000, write8smo_delegate(*this, FUNC(bbc_memexb20_device::disable_w)));
+
+	m_ram = make_unique_clear<uint8_t[]>(0x5000);
+
+	/* register for save states */
+	save_item(NAME(m_shadow));
+	save_pointer(NAME(m_ram), 0x5000);
+}
+
+
+//**************************************************************************
+//  IMPLEMENTATION
+//**************************************************************************
+
+void bbc_memexb20_device::enable_w(uint8_t data)
+{
+	m_shadow = true;
+}
+
+void bbc_memexb20_device::disable_w(uint8_t data)
+{
+	m_shadow = false;
+}
+
+uint8_t bbc_memexb20_device::ram_r(offs_t offset)
+{
+	uint8_t data = 0xff;
+
+	if (m_shadow && offset >= 0x3000)
+		data = m_ram[offset - 0x3000];
+	else
+		data = m_mb_ram->pointer()[offset];
+
+	return data;
+}
+
+void bbc_memexb20_device::ram_w(offs_t offset, uint8_t data)
+{
+	if (m_shadow && offset >= 0x3000)
+		m_ram[offset - 0x3000] = data;
+	else
+		m_mb_ram->pointer()[offset] = data;
+}

src/devices/bus/bbc/internal/memex.h

@@ -0,0 +1,50 @@
+// license:BSD-3-Clause
+// copyright-holders:Nigel Barnes
+/**********************************************************************
+
+    Memex B20 20K RAM expansion
+
+**********************************************************************/
+
+
+#ifndef MAME_BUS_BBC_INTERNAL_MEMEX_H
+#define MAME_BUS_BBC_INTERNAL_MEMEX_H
+
+#include "internal.h"
+
+
+//**************************************************************************
+//  TYPE DEFINITIONS
+//**************************************************************************
+
+class bbc_memexb20_device : public device_t, public device_bbc_internal_interface
+{
+public:
+	// construction/destruction
+	bbc_memexb20_device(const machine_config &mconfig, const char *tag, device_t *owner, uint32_t clock);
+
+protected:
+	// device-level overrides
+	virtual void device_start() override;
+
+	// optional information overrides
+	virtual const tiny_rom_entry *device_rom_region() const override;
+
+	virtual bool overrides_ram() override { return true; }
+	virtual uint8_t ram_r(offs_t offset) override;
+	virtual void ram_w(offs_t offset, uint8_t data) override;
+
+private:
+	void enable_w(uint8_t data);
+	void disable_w(uint8_t data);
+
+	bool m_shadow;
+	std::unique_ptr<uint8_t[]> m_ram;
+};
+
+
+// device type definition
+DECLARE_DEVICE_TYPE(BBC_MEMEXB20, bbc_memexb20_device);
+
+
+#endif /* MAME_BUS_BBC_INTERNAL_MEMEX_H */