ROM_FD_RW
#define ROM_FD_READ(u, s, c, a) ROM_FD_RW(u, s, c, a)
#define ROM_FD_WRITE(u, s, c, a) ROM_FD_RW(u | 0x1000, s, c, a)
err = ROM_FD_RW(0, pos, cnt, buf);
err = ROM_FD_RW(flag | __disk.unit, pos, cnt * 2, buf);
err = ROM_FD_RW(flag | __disk.unit | 0x1000000, pos, cnt, buf);