I’m Tomu, a tiny ARM microprocessor which fits in your USB port. I have two buttons and two LEDs!
I’m fully open source and am buildable by hobbyists! Designed for 2-factor authentication, usb experiments, or anything else you can think of.
I’m also available on Crowd Supply, fully assembled and tested.
Got a Tomu? Great! Here’s how to get started. First you need a case, then you need to figure out which bootloader you have.
Because Tomu fits entirely inside your USB port, you need something to keep it from falling out. Early Tomu prototypes were held in place using a business card folded over and wedged in the USB port, but newer releases have support for 3D printed cases.
If you have a 3D printer, download the .stl file for the version of Tomu that you have. The version number is printed on the bottom side with the big USB connections. Depending on how thick your PCB is, you may need to adjust the FreeCAD file.
There are two types of bootloaders for Tomu: Serial and DFU. If you got your board from Crowd Supply, or updated it using the test jig at LCA 2018, or the LEDs blink red/green when you plug it in, then you have DFU. Otherwise, you have Serial.
Serial Bootloader (Legacy)
The serial bootloader is from SiLabs, and is known as AN0042.
To use the serial bootloader, Windows users will need to install Silabs-CDC_Install.zip, e.g. from M-Pression. Linux and macOS users do not need to use any special drivers. The device will show up as something like /dev/ttyUSB0.
- Enter the bootloader.
- v0.2 boards require you to connect the C pin to Vcc.
- v0.3 boards always enter the bootloader
- Connect a terminal.
- TeraTerm on Windows is a good choice
- screen works on Linux and macOS
- Interact with the bootloader by sending one-character commands:
- i – show the bootloader version
- u – upload a new program - send the binary using XMODEM
- b – boot the current program
Note that the ‘d’ command will delete the bootloader, so use with caution!!!
Toboot (DFU Bootloader)
The name of the DFU bootloader is Toboot. DFU is a USB standard for updating firmware on a device. The canonical program to use is dfu-util, which is in most major Linux distributions. When Tomu is in Bootloader mode, it will flash red/green, and show up when you run dfu-util -l.
Version 1.0 of Toboot will auto-run a program if one exists. That means that once you load the Sample program, Toboot will always run the sample program. To get back into Toboot, you will need to connect both capacitive buttons when you apply power. Tweezers are useful here. A future version of Toboot will have a “developer mode” that will cause it to always boot into DFU mode.
To load a program, run dfu-util -D [program].bin. Toboot will flash the new program onto your Tomu and reboot. Don’t worry if you flash the wrong file, or flash an invalid program – Toboot will detect this and reboot into DFU mode if the file you flash fails to run.
Tomu is crowdfunding on Crowd Supply! We have met the following stretch goals, and their development is already underway:
We would like a bootloader that gets out of the way and lets you run your normal application without needing to short out the C pin every time. We’d also like to not require drivers, or superuser access, or have to deal with other programs thinking Tomu is a GPS or modem (unless it’s behaving like one.) These are all shortcomings that the current bootloader suffers from.
Enough people have backed Tomu that we have developed an initial DFU bootloader that meets all these goals. Although the initial version is ready, it has some wrinkles that we intend to iron out before shipment.
Injection-Molded Plastic Case
Tomu is tiny, and fits entirely inside your USB port. USB ports have metal shields around them, so Tomu requires a case both to fit snugly inside the port and to protect the components from shorting out against the shield.
The current solution is to 3D print your own case. Since we’ve met this stretch goal, we’ve redesigned the board and have begun working on a steel tool to injection-mold a plastic case.
U2F / FIDO Firmware
GNU Chopstx has been ported to Tomu, complete with U2F support. That means you can use Tomu like any U2F token to add a second authentication factor when you log in. Chrome supports U2F natively, and Firefox supports it via a flag (and will support it fully in a few months)
The U2F firmware source is located on Github in im-tomu/chopstx/u2f.
To build the U2F firmware, ensure you have an ARM compiler installed (e.g. sudo apt install gcc-arm-none-eabi) as well as Python pip (e.g. pip install –user –upgrade asn1crypto), then run:
- pip install –user –upgrade asn1crypto
- git clone https://github.com/im-tomu/chopstx.git tomu-u2f
- cd tomu-u2f/u2f
Loading onto Tomu
The build system produces an output file build/u2f.bin. Upload this file to Tomu.
- If using the serial bootloader, type u and send the file using XMODEM
- If using the DFU bootloader, reboot into DFU mode and run dfu-util -D build/u2f.bin
These are currently the top items which need to be done related to the Tomu. If you help out, @mithro will probably send you a Tomu device!
Creating (or porting) a FOSS USB stack to EFM32HG
To make it easy for people to develop new applications for the Tomu, we need a good USB stack which is compatible with the EFM32HG.
There are a couple of possible options:
- Porting LUFA - Someone seems to have already started the EFM32 series, just not the EFM32HG.
- Port ChibiOS
- Other options?
QEmu Emulation of the EFM32HG
We would like to have good emulation of the features in the EFM32HG309 processor so that people can write software for the board without having to have the hardware.
The biggest part of this is the emulation of the USB stack.
- Announcement mailing list - Low traffic list for announcements.
- Discussion mailing list - List for discussing development / new features / etc.
- IRC Channel - irc://irc.freenode.net/#tomu - IRC channel for discussing anything related to the project.
Built out of a 3d printed part + 2 layer “thin” PCB (0.4mm, 0.6mm or 0.8mm thick).
- 6mil traces
- 6mil clearance
- 0.3mm drill / 0.6mm vias
All Tomu boards have:
- At least 2 different color LEDs
- At least 2 touch buttons
- Status: Hardware complete, simple flashing firmware working. Needs proper firmware.
- GitHub Repository
- Uses a Silicon Labs Happy Gecko EFM32HG309
- 25MHz ARM Cortex-M0+
- 8kb^ RAM
- 64kb^ Flash
- USB 2.0 FS and LS
- Literally 12 parts
The important thing to note is that you need a PCB that is 0.8mm thickness or less. The default thickness is normally 1.0mm and 1.0mm is too thick.
These gerbers should be possible with the following manufacturers:
- (Tested) Hackvana
- (Undergoing testing) DirtyPCB
- (Undergoing testing) Seeed Studio
- (Yet to be ordered) OHS Park - 2 Layer 2oz 0.8mm Service
The Tomu hardware is under your choice of:
- the “Creative Commons Attribution-ShareAlike 4.0 International License” (CC BY-SA 4.0) full text of this license is included in the LICENSE file and a copy can also be found at http://creativecommons.org/licenses/by-sa/4.0/
- the “TAPR Open Hardware License” full text of this license is included in the LICENSE file and a copy can also be found at http://www.tapr.org/OHL
Software for Tomu is under various licenses, please consult the license included with the code.