public void handler(int offset, int data) {
            UBytePtr RAM = memory_region(REGION_CPU1);

            if (data != 0) {
                /* swap ROM 2 and 3! */
                cpu_setbank(1, new UBytePtr(RAM, 0x3000));
                cpu_setbank(2, new UBytePtr(RAM, 0x2000));
            } else {
                cpu_setbank(1, new UBytePtr(RAM, 0x2000));
                cpu_setbank(2, new UBytePtr(RAM, 0x3000));
            }
        }