def _connect_attempt(self, mode='default_reset', esp32r0_delay=False):
        """ A single connection attempt, with esp32r0 workaround options """
        # esp32r0_delay is a workaround for bugs with the most common auto reset
        # circuit and Windows, if the EN pin on the dev board does not have
        # enough capacitance.
        #
        # Newer dev boards shouldn't have this problem (higher value capacitor
        # on the EN pin), and ESP32 revision 1 can't use this workaround as it
        # relies on a silicon bug.
        #
        # Details: https://github.com/espressif/esptool/issues/136
        last_error = None

        # If we're doing no_sync, we're likely communicating as a pass through
        # with an intermediate device to the ESP32
        if mode == "no_reset_no_sync":
            return last_error

        # issue reset-to-bootloader:
        # RTS = either CH_PD/EN or nRESET (both active low = chip in reset
        # DTR = GPIO0 (active low = boot to flasher)
        #
        # DTR & RTS are active low signals,
        # ie True = pin @ 0V, False = pin @ VCC.
        if mode != 'no_reset':
            self._setDTR(False)  # IO0=HIGH
            self._setRTS(True)   # EN=LOW, chip in reset
            time.sleep(0.1)
            if esp32r0_delay:
                # Some chips are more likely to trigger the esp32r0
                # watchdog reset silicon bug if they're held with EN=LOW
                # for a longer period
                time.sleep(1.2)
            self._setDTR(True)   # IO0=LOW
            self._setRTS(False)  # EN=HIGH, chip out of reset
            if esp32r0_delay:
                # Sleep longer after reset.
                # This workaround only works on revision 0 ESP32 chips,
                # it exploits a silicon bug spurious watchdog reset.
                time.sleep(0.4)  # allow watchdog reset to occur
            time.sleep(0.05)
            self._setDTR(False)  # IO0=HIGH, done

        for _ in range(5):
            try:
                self.flush_input()
                self._port.flushOutput()
                self.sync()
                return None
            except FatalError as e:
                if esp32r0_delay:
                    print('_', end='')
                else:
                    print('.', end='')
                sys.stdout.flush()
                time.sleep(0.05)
                last_error = e
        return last_error