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cartridge.go
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/
cartridge.go
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// Package cartridge provides .nes ROM loading and saving.
package cartridge
import (
"encoding/binary"
"fmt"
"io"
)
// Cartridge contains a NES cartridge content.
type Cartridge struct {
PRG []byte // PRG-ROM banks
CHR []byte // CHR-ROM banks
RAM byte // PRG-RAM banks
Trainer []byte
Mapper byte // mapper type
Mirror MirrorMode // mirroring mode
Battery byte // battery present
VideoFormat byte // 0 NTSC, 1 PAL
}
// New returns a new cartridge.
func New() *Cartridge {
return &Cartridge{
PRG: make([]byte, 0x8000),
CHR: make([]byte, 0x2000),
Mapper: 0,
Mirror: MirrorVertical,
Battery: 0,
}
}
// Save the cartridge content in iNES format.
func (c *Cartridge) Save(writer io.Writer) error {
header := header{
Magic: iNESFileMagic,
NumPRG: byte(len(c.PRG) / 16384),
NumCHR: byte(len(c.CHR) / 8192),
NumRAM: c.RAM,
VideoFormat: c.VideoFormat,
}
header.Control1, header.Control2 = ControlBytes(c.Battery, byte(c.Mirror), c.Mapper, len(c.Trainer) > 0)
if err := binary.Write(writer, binary.LittleEndian, header); err != nil {
return fmt.Errorf("writing header: %w", err)
}
if len(c.Trainer) > 0 {
if err := binary.Write(writer, binary.LittleEndian, c.Trainer); err != nil {
return fmt.Errorf("writing trainer: %w", err)
}
}
if err := binary.Write(writer, binary.LittleEndian, c.PRG); err != nil {
return fmt.Errorf("writing PRG: %w", err)
}
if len(c.CHR) > 0 {
if err := binary.Write(writer, binary.LittleEndian, c.CHR); err != nil {
return fmt.Errorf("writing CHR: %w", err)
}
}
return nil
}