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Author: mmoskal

README.md

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+# UF2 Bootloader for Arduino UNO R3
+
+This projects allows flashing of Arduino UNO R3 via USB Mass Storage
+(i.e., file copy or drag and drop without needed to install any software).
+
+It implements it in firmware of the ATmega16u2 - the USB interface chip
+on the Arduino UNO. This firmware in turn talks to the `optiboot` bootloader
+running on the main ATmega328p chip.
+
+The mass storage interface accepts files in [UF2](https://github.com/microsoft/uf2)
+format. The new format (i.e., not `.hex` and not `.bin`) is necessary to implement
+a reliable mass storage flashing in the 512 bytes of RAM of the ATmega. The UF2 repository
+contains some conversion tools.
+
+## Building
+
+```
+$ git clone https://github.com/abcminiuser/lufa lufa
+$ cd lufa/Projects
+$ git clone https://github.com/microsoft/uf2-uno
+$ cd uf2-uno
+$ make
+```
+
+I'm using LUFA `170418` right now. You need to have `avr-gcc` etc in `PATH`.
+I'm using 4.9.
+
+## Installing
+
+* place the ATmega in DFU update mode by shorting two pins sticking out closest to the USB plug
+* under macOS or Linux install `dfu-programer` and run `make burn`
+* under Windows use [Atmel FLIP](http://www.atmel.com/tools/flip.aspx)
+
+Arduino provides [more detailed instructions](https://www.arduino.cc/en/Hacking/DFUProgramming8U2).
+
+Note: this bootloader is not currently compatible with Arduino IDE. If you want
+that, go back to the original bootloader (also following the instructions from the Arduino
+page above).
+
+## HID
+
+The firmware exposes a custom raw HID interface, implementing a small subset of 
+[HF2 protocol](https://github.com/microsoft/uf2/blob/master/hf2.md), in particular
+the serial-forwarding parts. The serial can be accessed using the C-based
+`uf2tool` or using [PXT command line](https://makecode.com/cli).
+
+## License
+
+MIT
+
+This code is based on the Mass Storage example from [LUFA](),
+has a few lines and the RingBuffer from the [Arduino USBSERIAL firmware](),
+and lifts some code from the [SAMD21 UF2 Bootloader](https://github.com/microsoft/uf2-samd21).
+All these are MIT licensed.