mapper_parkerbros.go

// This file is part of Gopher2600.
//
// Gopher2600 is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Gopher2600 is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Gopher2600.  If not, see <https://www.gnu.org/licenses/>.

package cartridge

import (
	"fmt"

	"github.com/jetsetilly/gopher2600/environment"
	"github.com/jetsetilly/gopher2600/hardware/memory/cartridge/mapper"
	"github.com/jetsetilly/gopher2600/hardware/memory/memorymap"
)

// from bankswitch_sizes.txt:
//
// -E0: Parker Brothers was the main user of this method.  This cart is
// segmented into 4 1K segments.  Each segment can point to one 1K slice of the
// ROM image.  You select the desired 1K slice by accessing 1FE0 to 1FE7 for
// the first 1K (1FE0 selects slice 0, 1FE1 selects slice 1, etc).  1FE8 to
// 1FEF selects the slice for the second 1K, and 1FF0 to 1FF8 selects the slice
// for the third 1K.  The last 1K always points to the last 1K of the ROM image
// so that the cart always starts up in the exact same place.
//
// cartridges:
//   - Montezuma's Revenge
//   - Lord of the Rings
//   - etc.
type parkerBros struct {
	env *environment.Environment

	mappingID string

	// parkerBros cartridges have 8 banks of 1024 bytes
	bankSize int
	banks    [][]uint8

	// rewindable state
	state *parkerBrosState
}

func newParkerBros(env *environment.Environment, data []byte) (mapper.CartMapper, error) {
	cart := &parkerBros{
		env:       env,
		mappingID: "E0",
		bankSize:  1024,
		state:     newParkerBrosState(),
	}

	cart.banks = make([][]uint8, cart.NumBanks())

	if len(data) != cart.bankSize*cart.NumBanks() {
		return nil, fmt.Errorf("E0: wrong number of bytes in the cartridge data")
	}

	for k := 0; k < cart.NumBanks(); k++ {
		cart.banks[k] = make([]uint8, cart.bankSize)
		offset := k * cart.bankSize
		copy(cart.banks[k], data[offset:offset+cart.bankSize])
	}

	return cart, nil
}

// MappedBanks implements the mapper.CartMapper interface.
func (cart *parkerBros) MappedBanks() string {
	return fmt.Sprintf("Banks: %d %d %d %d", cart.state.segment[0], cart.state.segment[1], cart.state.segment[2], cart.state.segment[3])
}

// ID implements the mapper.CartMapper interface.
func (cart *parkerBros) ID() string {
	return cart.mappingID
}

// Snapshot implements the mapper.CartMapper interface.
func (cart *parkerBros) Snapshot() mapper.CartMapper {
	n := *cart
	n.state = cart.state.Snapshot()
	return &n
}

// Plumb implements the mapper.CartMapper interface.
func (cart *parkerBros) Plumb(env *environment.Environment) {
	cart.env = env
}

// Reset implements the mapper.CartMapper interface.
func (cart *parkerBros) Reset() {
	cart.state.segment[0] = cart.NumBanks() - 4
	cart.state.segment[1] = cart.NumBanks() - 3
	cart.state.segment[2] = cart.NumBanks() - 2
	cart.state.segment[3] = cart.NumBanks() - 1
}

// Access implements the mapper.CartMapper interface.
func (cart *parkerBros) Access(addr uint16, peek bool) (uint8, uint8, error) {
	var data uint8
	if addr >= 0x0000 && addr <= 0x03ff {
		data = cart.banks[cart.state.segment[0]][addr&0x03ff]
	} else if addr >= 0x0400 && addr <= 0x07ff {
		data = cart.banks[cart.state.segment[1]][addr&0x03ff]
	} else if addr >= 0x0800 && addr <= 0x0bff {
		data = cart.banks[cart.state.segment[2]][addr&0x03ff]
	} else if addr >= 0x0c00 && addr <= 0x0fff {
		data = cart.banks[cart.state.segment[3]][addr&0x03ff]
	}

	if !peek {
		cart.bankswitch(addr)
	}

	return data, mapper.CartDrivenPins, nil
}

// AccessVolatile implements the mapper.CartMapper interface.
func (cart *parkerBros) AccessVolatile(addr uint16, data uint8, poke bool) error {
	if !poke {
		if cart.bankswitch(addr) {
			return nil
		}
	}

	if poke {
		if addr >= 0x0000 && addr <= 0x03ff {
			cart.banks[cart.state.segment[0]][addr&0x3ff] = data
		} else if addr >= 0x0400 && addr <= 0x07ff {
			cart.banks[cart.state.segment[1]][addr&0x3ff] = data
		} else if addr >= 0x0800 && addr <= 0x0bff {
			cart.banks[cart.state.segment[2]][addr&0x3ff] = data
		} else if addr >= 0x0c00 && addr <= 0x0fff {
			cart.banks[cart.state.segment[3]][addr&0x3ff] = data
		}
		return nil
	}

	return nil
}

// bankswitch on hotspot access. returns false if address wasn't recognised
func (cart *parkerBros) bankswitch(addr uint16) bool {
	if addr >= 0xfe0 && addr <= 0xff7 {
		switch addr {
		// segment 0
		case 0x0fe0:
			cart.state.segment[0] = 0
		case 0x0fe1:
			cart.state.segment[0] = 1
		case 0x0fe2:
			cart.state.segment[0] = 2
		case 0x0fe3:
			cart.state.segment[0] = 3
		case 0x0fe4:
			cart.state.segment[0] = 4
		case 0x0fe5:
			cart.state.segment[0] = 5
		case 0x0fe6:
			cart.state.segment[0] = 6
		case 0x0fe7:
			cart.state.segment[0] = 7

		// segment 1
		case 0x0fe8:
			cart.state.segment[1] = 0
		case 0x0fe9:
			cart.state.segment[1] = 1
		case 0x0fea:
			cart.state.segment[1] = 2
		case 0x0feb:
			cart.state.segment[1] = 3
		case 0x0fec:
			cart.state.segment[1] = 4
		case 0x0fed:
			cart.state.segment[1] = 5
		case 0x0fee:
			cart.state.segment[1] = 6
		case 0x0fef:
			cart.state.segment[1] = 7

		// segment 2
		case 0x0ff0:
			cart.state.segment[2] = 0
		case 0x0ff1:
			cart.state.segment[2] = 1
		case 0x0ff2:
			cart.state.segment[2] = 2
		case 0x0ff3:
			cart.state.segment[2] = 3
		case 0x0ff4:
			cart.state.segment[2] = 4
		case 0x0ff5:
			cart.state.segment[2] = 5
		case 0x0ff6:
			cart.state.segment[2] = 6
		case 0x0ff7:
			cart.state.segment[2] = 7
		}

		return true
	}

	return false
}

// NumBanks implements the mapper.CartMapper interface.
func (cart *parkerBros) NumBanks() int {
	return 8
}

// GetBank implements the mapper.CartMapper interface.
func (cart *parkerBros) GetBank(addr uint16) mapper.BankInfo {
	var seg int
	if addr >= 0x0000 && addr <= 0x03ff {
		seg = 0
	} else if addr >= 0x0400 && addr <= 0x07ff {
		seg = 1
	} else if addr >= 0x0800 && addr <= 0x0bff {
		seg = 2
	} else { // remaining address is between 0x0c00 and 0x0fff
		seg = 3
	}

	return mapper.BankInfo{Number: cart.state.segment[seg], IsRAM: false, IsSegmented: true, Segment: seg}
}

// Patch implements the mapper.CartMapper interface.
func (cart *parkerBros) Patch(offset int, data uint8) error {
	if offset >= cart.bankSize*len(cart.banks) {
		return fmt.Errorf("E0: patch offset too high (%d)", offset)
	}

	bank := offset / cart.bankSize
	offset %= cart.bankSize
	cart.banks[bank][offset] = data
	return nil
}

// AccessPassive implements the mapper.CartMapper interface.
func (cart *parkerBros) AccessPassive(_ uint16, _ uint8) {
}

// Step implements the mapper.CartMapper interface.
func (cart *parkerBros) Step(_ float32) {
}

// IterateBank implements the mapper.CartMapper interface.
func (cart *parkerBros) CopyBanks() []mapper.BankContent {
	c := make([]mapper.BankContent, len(cart.banks))

	// banks 0 to len-1 can occupy any of the three segments
	for b := 0; b < len(cart.banks)-1; b++ {
		c[b] = mapper.BankContent{Number: b,
			Data: cart.banks[b],
			Origins: []uint16{
				memorymap.OriginCart,
				memorymap.OriginCart + uint16(cart.bankSize),
				memorymap.OriginCart + uint16(cart.bankSize)*2,
			},
		}
	}

	// last bank can occupy any of the four segments (the last segment always
	// points to bank 7 but bank 7 can also be in another segment at the
	// same time)
	b := len(cart.banks) - 1
	c[b] = mapper.BankContent{Number: b,
		Data: cart.banks[b],
		Origins: []uint16{
			memorymap.OriginCart,
			memorymap.OriginCart + uint16(cart.bankSize),
			memorymap.OriginCart + uint16(cart.bankSize)*2,
			memorymap.OriginCart + uint16(cart.bankSize)*3,
		},
	}
	return c
}

// ReadHotspots implements the mapper.CartHotspotsBus interface.
func (cart *parkerBros) ReadHotspots() map[uint16]mapper.CartHotspotInfo {
	return map[uint16]mapper.CartHotspotInfo{
		// segment 0
		0x1fe0: {Symbol: "B0S0", Action: mapper.HotspotBankSwitch},
		0x1fe1: {Symbol: "B1S0", Action: mapper.HotspotBankSwitch},
		0x1fe2: {Symbol: "B2S0", Action: mapper.HotspotBankSwitch},
		0x1fe3: {Symbol: "B3S0", Action: mapper.HotspotBankSwitch},
		0x1fe4: {Symbol: "B4S0", Action: mapper.HotspotBankSwitch},
		0x1fe5: {Symbol: "B5S0", Action: mapper.HotspotBankSwitch},
		0x1fe6: {Symbol: "B6S0", Action: mapper.HotspotBankSwitch},
		0x1fe7: {Symbol: "B7S0", Action: mapper.HotspotBankSwitch},

		// segment 1
		0x1fe8: {Symbol: "B0S1", Action: mapper.HotspotBankSwitch},
		0x1fe9: {Symbol: "B1S1", Action: mapper.HotspotBankSwitch},
		0x1fea: {Symbol: "B2S1", Action: mapper.HotspotBankSwitch},
		0x1feb: {Symbol: "B3S1", Action: mapper.HotspotBankSwitch},
		0x1fec: {Symbol: "B4S1", Action: mapper.HotspotBankSwitch},
		0x1fed: {Symbol: "B5S1", Action: mapper.HotspotBankSwitch},
		0x1fee: {Symbol: "B6S1", Action: mapper.HotspotBankSwitch},
		0x1fef: {Symbol: "B7S1", Action: mapper.HotspotBankSwitch},

		// segment 2
		0x1ff0: {Symbol: "B0S2", Action: mapper.HotspotBankSwitch},
		0x1ff1: {Symbol: "B1S2", Action: mapper.HotspotBankSwitch},
		0x1ff2: {Symbol: "B2S2", Action: mapper.HotspotBankSwitch},
		0x1ff3: {Symbol: "B3S2", Action: mapper.HotspotBankSwitch},
		0x1ff4: {Symbol: "B4S2", Action: mapper.HotspotBankSwitch},
		0x1ff5: {Symbol: "B5S2", Action: mapper.HotspotBankSwitch},
		0x1ff6: {Symbol: "B6S2", Action: mapper.HotspotBankSwitch},
		0x1ff7: {Symbol: "B7S2", Action: mapper.HotspotBankSwitch},
	}
}

// WriteHotspots implements the mapper.CartHotspotsBus interface.
func (cart *parkerBros) WriteHotspots() map[uint16]mapper.CartHotspotInfo {
	return cart.ReadHotspots()
}

// rewindable state for the parker bros. cartridges.
type parkerBrosState struct {
	// parkerBros cartridges divide memory into 4 segments
	//  o the last segment always points to the last bank
	//  o the other segments can point to any one of the eight banks in the ROM
	//		(including the last bank)
	segment [4]int
}

func newParkerBrosState() *parkerBrosState {
	return &parkerBrosState{}
}

// Snapshot implements the mapper.CartMapper interface.
func (s *parkerBrosState) Snapshot() *parkerBrosState {
	n := *s
	return &n
}