Hacking_and_Penetration_Testing_with_Low_Power_Devices

BeagleBone capes
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pull-up resistor. Pins A0 and A1 should also be tied high, but two jumpers or dip
switches must be used to allow these pins to be tied low. This 2-bit addressing of
capes allows up to four capes to be installed assuming that the signals used by each
cape allow interoperation.
After a BeagleBone has booted, a cape manager process will read the EEPROMs
of all connected capes. The format for the EEPROM data can be found in the System
Reference Manual. Data stored include board name, manufacturer, version, number
of pins used, maximum currents on each bus, and pin configuration information.
There are 74 configurable pins out of the 92 pins on the BeagleBone expansion
headers. Two bytes is required to describe the configuration of each pin. The cape
manager uses this information to ensure proper cape configuration. A prototype
board or other cape that lacks an EEPROM will require that appropriate device tree
overlays be manually loaded. Device tree overlays will be described briefly later in
this chapter.
XBee MINI-CAPE
As previously discussed, we will use IEEE 802.15.4 or XBee networking to remotely
command our army of hacking drones. If you want more than just a few drones, using
a cape to connect your XBee modems might be preferable to hardwiring the modems
as described early in this chapter. We’ll get our feet wet with an XBee min-cape.
The mini-cape presented here is easily built with hobby printed circuit board
(PCB) kits. The single-sided (copper trace on one side only) board is a mere 1.25
2.20 in.. Several of these can be made from commonly available board sizes. There
are a number of ways to produce small circuit boards. Do not fear if you have never
done something like this before.
The mini-cape and other boards presented in this book were created using the
popular EAGLE CAD software from CadSoft (http://www.cadsoftusa.com/eaglepcb-design-software).
CadSoft offers a lot of EAGLE licensing levels. There is a free
version of EAGLE limited to smaller boards with two or less signal layers that are
more than sufficient for creating BeagleBone capes.
The schematic for the mini-cape is shown in Figure 6.6. Connectors JP1 and JP2
connect to expansion headers P9 and P8, respectively. JP1 and JP2 are connected to
pins 1-22 and 1-10, respectively. Power is supplied by the first four pins on P9. Pins 1
and 2 are ground. The BeagleBone provides 3.3 V power on pins 3 and 4. The LEDs
for XBee power and association are optional. Eliminating the LEDs reduces power
consumption and also makes the cape more stealthy.
One possible use of P9 pins 21 and 22 is UART2 (TTYO2) transmit and receive,
respectively. Recall that the complete set of possibilities for all of the expansion
header pins can be found in the System Reference Manual. P9 pins 21 and 22 are
connected to DIN and DOUT, respectively, on the XBee modem.
The two connections on P8 are both optional. Pins 7 and 9 on P8 can be used as
general-purpose input/output (GPIO) pins. Pin 7 is tied to the XBee reset pin. The
reset pin is active low, which means that connecting this pin to ground for more than