Accessory

USB armory Mk II debug accessory

The USB armory is an open source hardware design, implementing a flash drive sized computer.

The USB armory Mk II exposes a USB Type-C receptacle, which allows through the so called USB-C 'debug accessory mode' to route analog/debug signals over its connector, the USB armory Mk II design leverages on this to break out UART, SPI, I²C, CAN (pre-transceiver), GPIOs connections to/from its application processor.

The debug accessory board allows to access UART and GPIO signals through USB, without requiring probes, through an FTDI FT4232H. This allows, for example, access to the USB armory Mk II serial console without wires or probes, natively using only USB cables. All other interfaces can be accessed through dedicated breakout through holes.

This repository is aimed towards developers, if you wish to purchase a USB armory board please see the USB armory documentation.

PCB Information

2 layers, 0.80mm thickness, top only components
Outer layers 0.5 oz base copper foil
Inner layers 1 oz base copper foil
width (X) 45.65 mm, height (Y) 25.90 mm
Red soldermask, white component legend

Bill of materials

DRC information

Minimum track width: 0.127 mm
Minimum via diameter: 0.450 mm
Outer layer track width: 0.127 mm
Outer layer isolation distance: 0.127 mm
Outer layer annular ring: 0.100 mm
Smallest final hole (plated): 0.150 mm

Errata

The silkscreen labels for 3.3V and 5V are inverted on all rev v1 PCBs, see this issue.

USB armory Mk II debug I/Os

NOTE: the connection between the debug accessory and the target is supported only with the same orientation for both top layers (side with components for the accessory, side with LEDs for the USB armory).

The following table summarizes the available configurations on the USB armory Mk II through debug accessory mode, which are exposed on its Type-C receptacle port.

¹ Only on USB armory Mk II boards mounting i.MX6UL SoC, not available on versions mounting the i.MX6ULZ.

Serial console

When running the USB armory Debian base image the serial console (UART2) can be accessed, with the debug accessory jumper set to UART position, as follows (example on Linux host with picocom):

picocom -b 115200 -eb /dev/ttyUSB2 --imap lfcrlf

Debug accessory jumper settings

Power source

The debug accessory always acts as a power source and is meant to be connected exclusively to the USB armory Mk II Type-C receptacle port. The USB armory Mk II Type-C can be safely plugged on a different receptacle as the board can handle two power sources simultaneously.

It is not recommended to connect the debug accessory to anything other than the USB armory Mk II, however in case this happens compliant Type-C receptacles should handle the situation gracefully¹ without concerns.

¹ USB Type-C Cable and Connector Specification (1.3, 2017-07-14): "Legacy hosts/chargers that by default source VBUS when connected using any legacy USB connector (Standard-A, Micro-B, etc.) to USB Type-C cable or adapter are exempted from these two requirements."

I/O mode

The GPIO and UART functions can be used directly using the FTDI FT4232H USB interface accessible on the Micro USB Type-B connector, all other modes can be accessed using the exposed breakout through holes.

The following table illustrates the required jumper positions and interfaces for each available I/O mode.

¹ The GPIO header position refers to termination either of the two pins facing the "GPIO" label (GPIO position, pins towards positions 3 and 2) or the opposite position (!GPIO position, pins towards positions 2 and 1).

² Any position can be used as the FTDI is not used in such mode.

Pin assignment: GPIO

Pin assignment: UART2

¹ On USB armory Mk II rev. β see the related errata.

Pin assignment: UART4

Pin assignment: UART5

Physical access: UART2

When no debug accessory is available, the serial console (UART2) can be also accessed with a USB-C plug breakout and a USB to 3.3 TTL serial cable with the following configuration.

License

USB armory | https://github.com/usbarmory/usbarmory
Copyright (c) The USB armory authors

This is an open hardware design licensed under the terms of the CERN Open Hardware Licence (OHL) v1.2.

You may redistribute and modify this documentation under the terms of the CERN OHL v.1.2 (http://ohwr.org/cernohl). This documentation is distributed WITHOUT ANY EXPRESS OR IMPLIED WARRANTY, INCLUDING OF MERCHANTABILITY, SATISFACTORY QUALITY AND FITNESS FOR A PARTICULAR PURPOSE. Please see the CERN OHL v.1.2 for applicable conditions.

The following exceptions apply:

• ../lib.snapeda: all files in this directory are imported or modified from SnapEDA symbols and footprints, therefore the license at https://www.snapeda.com/about/FAQ/#license applies.