Using The Second Microcontroller On An Arduino

While newer Arduinos and Arduino compatibles (including the Hackaday.io Trinket Pro. Superliminal Advertising!) either have a chip capable of USB or rely on a V-USB implementation, the old fogies of the Arduino world, the Uno and Mega, actually have two chips. An ATMega16u2 takes care of the USB connection, while the standard ‘328 or ‘2560 takes care of all ~duino tasks. Wouldn’t it be great is you could also use the ’16u2 on the Uno or Mega for some additional functionality to your Arduino sketch? That’s now a reality. [Nico] has been working on the HoodLoader2 for a while now, and the current version give you the option of reprogramming the ’16u2 with custom sketches, and use seven I/O pins on this previously overlooked chip.

Unlike the previous HoodLoader, this version is a real bootloader for the ’16u2 that replaces the DFU bootloader with a CDC bootloader and USB serial function. This allows for new USB functions like HID keyboard, mouse, media keys, and a gamepad, the addition of extra sensors or LEDs, and anything else you can do with a normal ‘duino.

Setup is simple enough, only requiring a connection between the ‘328 ISP header and the pins on the ’16u2 header. There are already a few samples of what this new firmware for the ’16u2 can do over on [Nico]’s blog, but we’ll expect the number of example projects using this new bootloader to explode over the coming months. If you’re ever in an Arduino Demoscene contest with an Arduino and you’re looking for more pins and code space, now you know where to look.

Exploiting DFU mode to snag a copy of firmware upgrades

[Travis Goodspeed] continues his work at educating the masses on how to reverse engineer closed hardware devices. This time around he’s showing us how to exploit the Device Firmware Updates protocol in order to get your hands on firmware images. It’s a relatively easy technique that uses a man-in-the-middle attack to dump the firmware image directly to a terminal window. This way you can get down to the nitty-gritty of decompiling and hex editing as quickly as possible.

For this hack he used his Facedancer board. We first saw the hardware used to emulate a USB device, allowing the user to send USB commands via software. Now it’s being used to emulate your victim hardware’s DFU mode. This is done by supplying the vendorID and productID of the victim, then pushing the firmware update as supplied by the manufacturer. In most cases this shouldn’t even require you to have the victim hardware on hand.

AVR programmer made without a programmer

[blueHash] uses this cheap development board as an AVR programmer. What’s interesting to us is that it solves the chicken-or-egg problem that is usually encountered when bootstrapping a programmer. We’ve written about this issue before. Most programmers use microcontrollers, which first need to be flashed using a programmer. But it turns out the chip on this dev board has a DFU mode which gets around that conundrum.

He grabbed a uSD dev board for about $6. It’s got a crystal, an ATmega32u4 chip, and on the other side there’s a MicroSD card slot. We looked around and found an Atmel Datasheet (PDF) which describes the Device Firmware Upgrade mechanism. The AVR devices which support DFU are factory configured to use it. This dev board is designed to use DFU so all [blueHash] needed to do is find and configure a ISP firmware package that worked with this chip.