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mapper_superbank.go
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mapper_superbank.go
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// 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"
"math/rand"
"github.com/jetsetilly/gopher2600/curated"
"github.com/jetsetilly/gopher2600/hardware/memory/bus"
"github.com/jetsetilly/gopher2600/hardware/memory/cartridge/mapper"
"github.com/jetsetilly/gopher2600/hardware/memory/memorymap"
)
type superbank struct {
mappingID string
description string
// superbank cartridges can have 32 banks (128k) or 64 banks (256k)
bankSize int
banks [][]uint8
// the mask we use to decide whether the listen() address will trigger a
// bankswitch. this will change depending on the exact size of the
// cartridge.
bankSwitchMask uint16
// rewindable state
state *superbankState
// !!TODO: hotspot info for superbank
}
func newSuperbank(data []byte) (mapper.CartMapper, error) {
cart := &superbank{
mappingID: "SB",
description: "Superbank",
bankSize: 4096,
state: newSuperbankState(),
}
if len(data)%cart.bankSize != 0 {
return nil, curated.Errorf("SB: %v", "wrong number of bytes in the cartridge data")
}
cart.banks = make([][]uint8, len(data)/cart.bankSize)
cart.bankSwitchMask = uint16(cart.NumBanks() - 1)
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
}
// Mapping implements the mapper.CartMapper interface.
func (cart *superbank) Mapping() string {
return fmt.Sprintf("Bank: %d", cart.state.bank)
}
// ID implements the mapper.CartMapper interface.
func (cart *superbank) ID() string {
return cart.mappingID
}
// Snapshot implements the mapper.CartMapper interface.
func (cart *superbank) Snapshot() mapper.CartMapper {
n := *cart
n.state = cart.state.Snapshot()
return &n
}
// Plumb implements the mapper.CartMapper interface.
func (cart *superbank) Plumb() {
}
// Reset implements the cartMapper interface.
func (cart *superbank) Reset(randSrc *rand.Rand) {
cart.state.bank = len(cart.banks) - 1
}
// Read implements the mapper.CartMapper interface.
func (cart *superbank) Read(addr uint16, passive bool) (uint8, error) {
return cart.banks[cart.state.bank][addr], nil
}
// Write implements the mapper.CartMapper interface.
func (cart *superbank) Write(addr uint16, data uint8, passive bool, poke bool) error {
if poke {
cart.banks[cart.state.bank][addr] = data
return nil
}
return curated.Errorf("SB: %v", curated.Errorf(bus.AddressError, addr))
}
// NumBanks implements the mapper.CartMapper interface.
func (cart *superbank) NumBanks() int {
return len(cart.banks)
}
// GetBank implements the mapper.CartMapper interface.
func (cart *superbank) GetBank(addr uint16) mapper.BankInfo {
// superbank cartridges are like atari cartridges in that the entire address
// space points to the selected bank
return mapper.BankInfo{Number: cart.state.bank, IsRAM: false}
}
// Patch implements the mapper.CartMapper interface.
func (cart *superbank) Patch(offset int, data uint8) error {
if offset >= cart.bankSize*len(cart.banks) {
return curated.Errorf("SB: %v", fmt.Errorf("patch offset too high (%v)", offset))
}
bank := offset / cart.bankSize
offset %= cart.bankSize
cart.banks[bank][offset] = data
return nil
}
// Listen implements the mapper.CartMapper interface.
func (cart *superbank) Listen(addr uint16, data uint8) {
// return with no side effect if address is not a TIA mirror
if addr&0x1800 != 0x0800 {
return
}
// switch banks if address is in range of the number of banks
bank := int(addr & cart.bankSwitchMask)
// belt and braces check (probably not necessary)
if bank < len(cart.banks) {
cart.state.bank = bank
}
}
// Step implements the mapper.CartMapper interface.
func (cart *superbank) Step(_ float32) {
}
// IterateBank implements the mapper.CartMapper interface.
func (cart *superbank) CopyBanks() []mapper.BankContent {
c := make([]mapper.BankContent, len(cart.banks))
for b := 0; b < len(cart.banks); b++ {
c[b] = mapper.BankContent{Number: b,
Data: cart.banks[b],
Origins: []uint16{memorymap.OriginCart},
}
}
return c
}
// rewindable state for the superbank cartridge.
type superbankState struct {
// identifies the currently selected bank
bank int
}
func newSuperbankState() *superbankState {
return &superbankState{}
}
// Snapshot implements the mapper.CartMapper interface.
func (s *superbankState) Snapshot() *superbankState {
n := *s
return &n
}