@Override
        // note: only working on some devices, on other devices ignored w/o error
        public void purgeHwBuffers(boolean purgeWriteBuffers, boolean purgeReadBuffers) throws IOException {
            int value = (purgeReadBuffers ? FLUSH_READ_CODE : 0)
                    | (purgeWriteBuffers ? FLUSH_WRITE_CODE : 0);

            if (value != 0) {
                setConfigSingle(SILABSER_FLUSH_REQUEST_CODE, value);
            }
        }
emulate external XON/OFF
@throws IOException
usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/Cp21xxSerialDriver.java