diff options
Diffstat (limited to 'src/devices/bus/bbc/rom/genie.cpp')
-rw-r--r-- | src/devices/bus/bbc/rom/genie.cpp | 115 |
1 files changed, 115 insertions, 0 deletions
diff --git a/src/devices/bus/bbc/rom/genie.cpp b/src/devices/bus/bbc/rom/genie.cpp new file mode 100644 index 00000000000..653d874525e --- /dev/null +++ b/src/devices/bus/bbc/rom/genie.cpp @@ -0,0 +1,115 @@ +// 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, uint32_t 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; +} |