// 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; }