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unrom.go
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unrom.go
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package nes
import (
"fmt"
"github.com/nwidger/nintengo/rp2ago3"
)
type UNROMRegisters struct {
BankSelect uint8
}
type UNROM struct {
*ROMFile `json:"-"`
Registers UNROMRegisters
}
func (reg *UNROMRegisters) Reset() {
reg.BankSelect = 0x00
}
func NewUNROM(romf *ROMFile) *UNROM {
unrom := &UNROM{
ROMFile: romf,
}
unrom.Registers.Reset()
return unrom
}
func (unrom *UNROM) String() string {
return unrom.ROMFile.String() +
fmt.Sprintf("Mapper: 2 (UNROM)")
}
func (unrom *UNROM) Mappings(which rp2ago3.Mapping) (fetch, store []uint16) {
fetch = []uint16{}
store = []uint16{}
switch which {
case rp2ago3.PPU:
if unrom.ROMFile.chrBanks > 0 {
// CHR bank 1
for i := uint32(0x0000); i <= 0x0fff; i++ {
fetch = append(fetch, uint16(i))
store = append(store, uint16(i))
}
// CHR bank 2
for i := uint32(0x1000); i <= 0x1fff; i++ {
fetch = append(fetch, uint16(i))
store = append(store, uint16(i))
}
}
case rp2ago3.CPU:
if unrom.ROMFile.prgBanks > 0 {
// PRG bank 1
for i := uint32(0x8000); i <= 0xbfff; i++ {
fetch = append(fetch, uint16(i))
store = append(store, uint16(i))
}
// PRG bank 2
for i := uint32(0xc000); i <= 0xffff; i++ {
fetch = append(fetch, uint16(i))
store = append(store, uint16(i))
}
}
}
return
}
func (unrom *UNROM) Reset() {
unrom.Registers.BankSelect = 0x00
}
func (unrom *UNROM) Fetch(address uint16) (value uint8) {
switch {
// PPU only
case address >= 0x0000 && address <= 0x1fff:
if unrom.ROMFile.chrBanks > 0 {
value = unrom.ROMFile.vromBanks[0][address]
}
// CPU only
case address >= 0x8000 && address <= 0xffff:
index := address & 0x3fff
switch {
// PRG bank 1
case address >= 0x8000 && address <= 0xbfff:
if unrom.ROMFile.prgBanks > 0 {
value = unrom.ROMFile.romBanks[unrom.Registers.BankSelect][index]
}
// PRG bank 2
case address >= 0xc000 && address <= 0xffff:
if unrom.ROMFile.prgBanks > 0 {
value = unrom.ROMFile.romBanks[unrom.ROMFile.prgBanks-1][index]
}
}
}
return
}
func (unrom *UNROM) Store(address uint16, value uint8) (oldValue uint8) {
// PPU only
switch {
// CHR banks 1 & 2
case address >= 0x0000 && address <= 0x1fff:
if unrom.ROMFile.chrBanks > 0 {
unrom.ROMFile.vromBanks[0][address] = value
}
// CPU only
// PRG banks 1 & 2
case address >= 0x8000 && address <= 0xffff:
unrom.Registers.BankSelect = value & 0x07
}
return
}