** WARNING ** Always use great care when working with powered ESC's that are connected to motors. Especially when reflashing firmware and reseting devices it is easily possible to get a situation where the motors start running on their own.

To use:

• Load this sketch on to your Arduino or similar with at least 512 bytes RAM.

• Hook up the serial port/USB from the Arduino to your computer.

• Make sure the ESC and Arduino have a common ground (GND) connection.

• Connect an ESC that has the simonk bootloader enabled by connecting the servo signal wire to PD2/INT0 on the Arduino. I recommend a 470 ohm resistor in series on this line as a general protective measure.

• Finally use something like avrdude or KKmulticopter Flash Tool to flash over the serial port at 19200 baud using STK500v2 protocol. Look at the simonk Makefile for avrdude usage examples.

Known issues: When applying power to the Arduino and the ESC at the same time the ESC will arm before we are able to set the signal pin HIGH. It will still work but be careful. Best is to connect and power the Arduino first then power up the ESC to ensure that it is held in the bootloader (there should be no beeps from the ESC).

Message sizes of more than 297 bytes (total) not not supported and will likely crash this software. The STK500 firmware is currently limited to 281 bytes so it is not an issue at this time.

Note that the default serial port rate is 19200 and this is separate from the servo wire signaling rate. Make sure your tools are using the same serial port rate.

Both the serial port baud rate and the signaling rate can be changed on the fly or stored in EEPROM, see below.

Advanced usage:

** WARNING ** It is critically important that you don't have multiple applications accessing the serial port at the same time. The Arduino serial monitor in particular because it holds the port open and intercepts data. Typically in this situation avrdude will get errors, recover, and then eventually finish successfully. HOWEVER, dispite finishing successfully your firmware will most likely be corrupted. This goes for both reading and writing over the serial port.

• The ArduinoUSBLinker supports run-time configuration of which pin to use for signaling and at what bit rate to run at. These options are configured by using text commands sent over the serial port.

  The command format is similar to but not the same as the MultiWii serial protocol. All messages start with "$M<" followed by a command character and its parameter(s). A description of how pin numbers are determined is below.

  Supported commands are:

  $M<Pn : Select pin number n. This will also set the pull-up resistor for the pin. The currently selected pin will be used for signaling. It is recommened to make one pass through all the ESC pins selecting each one before doing anything else. This will put them all in bootloader mode and prevent "no-signal" beeping. Example: "$M<P18" will select pin 18 (PD2/INT0).

  $M<Bn : Sets the bit time in microseconds. Example: "$M<B32" will set a 32µs signaling rate.

  $M<Rn : Sets the serial port baud rate. Only for non-MultiWii builds. In MultiWii builds this will always return "0" in the status line. Example: "$M<R115200" will set the serial port to 115200 bps.

  $M<W : Write the pin, bit time, and serial port baud to EEPROM. These will be restored on reset. Only for non-MultiWii builds.

  All commands, including invalid commands that start with "$M<" will print the current settings back over the serial port. The settings are followed by a list of all the ports and the starting pin number for each.

  Example status line: P18:B136:R9600:PINS:B0:C8:D16:

  Pin 18 is selected, bit rate is 136µs, baud rate is 9600, and there are 3 ports: PORTB starts with pin 0. PORTC starts with pin 8. PORTD starts with pin 16.

  This indicates pin 0-7 is PB0..7, pin 8-15 is PC0..7, pin 16-24 is PD0..7, and so on. These are the pin numbers used with the above commands.

• This sketch can be integrated with MultiWii and has been tested with MultiWii_shared latest SVN source. Copy the "ArduinoUSBLinker.ino" file in to the MultiWii sketch folder and rename it as "ArduinoUSBLinker.h". Apply the supplied patch "Serial.patch" to the MultiWii "Serial.ino" file.

  The ArduinoUSBLinker code adds approximately 1800 bytes to the firmware size and depending on which MultiWii options are configured there may not be enough room for everything.

  Baud rate for the serial interface is the same as MultiWii (usually 115200).

  To enter the ArduinoUSBLinker mode a MultiWii command 239 must be sent using the MultiWii serial protocol. This is a binary string of the following 6 characters (in hex): 24 4D 3C 00 EF EF
  In pseudo text: '$' 'M' '<' <datalen> <239> <checksum>

  Note the "239" command is subject to change and is not part of the official MultiWii code base.

  To exit ArduinoUSBLinker mode power cycle or reset the device.

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