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// license:BSD-3-Clause
// copyright-holders:Nigel Barnes
// thanks-to:Derek Mathieson (original author of Genie)
/***************************************************************************
PMS Genie
***************************************************************************/
#include "emu.h"
#include "genie.h"
//**************************************************************************
// DEVICE DEFINITIONS
//**************************************************************************
DEFINE_DEVICE_TYPE(BBC_PMSGENIE, bbc_pmsgenie_device, "bbc_pmsgenie", "PMS Genie ROM Board")
//**************************************************************************
// LIVE DEVICE
//**************************************************************************
//-------------------------------------------------
// bbc_palprom_device - constructor
//-------------------------------------------------
bbc_pmsgenie_device::bbc_pmsgenie_device(const machine_config &mconfig, const char *tag, device_t *owner, const XTAL &clock)
: device_t(mconfig, BBC_PMSGENIE, tag, owner, clock)
, device_bbc_rom_interface(mconfig, *this)
, m_write_latch(0)
, m_bank_latch(0)
{
}
//-------------------------------------------------
// device_start - device-specific startup
//-------------------------------------------------
void bbc_pmsgenie_device::device_start()
{
save_item(NAME(m_write_latch));
save_item(NAME(m_bank_latch));
}
//-------------------------------------------------
// read
//-------------------------------------------------
uint8_t bbc_pmsgenie_device::read(offs_t offset)
{
uint8_t data = 0xff;
if (!machine().side_effects_disabled())
{
switch (offset >> 8)
{
case 0x1e:
/* &9E00-&9EFF - Write value latch */
m_write_latch = offset & 0xff;
break;
case 0x1f:
/* &9F00-&9FFF - Bank select latch
Bit
0-2: RAM bank select
3: Not used
4-5: ROM bank select
6: Not used
7: Read / NOT Write for internal RAM */
m_bank_latch = offset & 0xff;
break;
}
}
switch (offset & 0x2000)
{
case 0x0000:
/* &8000-&9FFF - 4 Pages of 8K ROM (32K in total) */
data = get_rom_base()[(offset & 0x1fff) | (m_bank_latch & 0x30) << 9];
break;
case 0x2000:
/* &A000-&BFFF - 8 Pages of 8K RAM (64K in total) */
if (m_bank_latch & 0x80)
{
/* RAM read */
if (m_bank_latch & 0x04)
{
data = get_nvram_base()[(offset & 0x1fff) | (m_bank_latch & 0x03) << 13];
}
else
{
data = get_ram_base()[(offset & 0x1fff) | (m_bank_latch & 0x03) << 13];
}
}
else
{
/* RAM write */
if (m_bank_latch & 0x04)
{
get_nvram_base()[(offset & 0x1fff) | (m_bank_latch & 0x03) << 13] = m_write_latch;
}
else
{
get_ram_base()[(offset & 0x1fff) | (m_bank_latch & 0x03) << 13] = m_write_latch;
}
data = m_write_latch;
}
break;
}
return data;
}
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