Method updateOffsets

nes/mapper1.go:185–205

PRG ROM bank mode (0, 1: switch 32 KB at $8000, ignoring low bit of bank number; 2: fix first bank at $8000 and switch 16 KB bank at $C000; 3: fix last bank at $C000 and switch 16 KB bank at $8000) CHR ROM bank mode (0: switch 8 KB at a time; 1: switch two separate 4 KB banks)

()

//                    3: fix last bank at $C000 and switch 16 KB bank at $8000)
// CHR ROM bank mode (0: switch 8 KB at a time; 1: switch two separate 4 KB banks)
func (m *Mapper1) updateOffsets() {
	switch m.prgMode {
	case 0, 1:
		m.prgOffsets[0] = m.prgBankOffset(int(m.prgBank & 0xFE))
		m.prgOffsets[1] = m.prgBankOffset(int(m.prgBank | 0x01))
	case 2:
		m.prgOffsets[0] = 0
		m.prgOffsets[1] = m.prgBankOffset(int(m.prgBank))
	case 3:
		m.prgOffsets[0] = m.prgBankOffset(int(m.prgBank))
		m.prgOffsets[1] = m.prgBankOffset(-1)
	}
	switch m.chrMode {
	case 0:
		m.chrOffsets[0] = m.chrBankOffset(int(m.chrBank0 & 0xFE))
		m.chrOffsets[1] = m.chrBankOffset(int(m.chrBank0 | 0x01))
	case 1:
		m.chrOffsets[0] = m.chrBankOffset(int(m.chrBank0))
		m.chrOffsets[1] = m.chrBankOffset(int(m.chrBank1))
	}
}