Raspdancer

What?

Merging Facedancer & Raspberry Pi

Why?

Facedancer11 is a one-purpose version of the flexible GoodFET board.
It was well designed to move all the intelligence into the host controller, not in the embedded uC.
Facedancer11 hardware can be seen as:

 USBconn -- FT232RL -- MSP430F2618TPM -- MAX3420E -- USBconn

where the first two chips are only converting busses:

 USBconn -- FT232RL -- MSP430F2618TPM -- MAX3420E -- USBconn
         USB   <>   UART     <>       SPI   ...   (USB)

BoM view (Farnell prices with tax):

 USBconn -- FT232RL -- MSP430F2618TPM -- MAX3420E -- USBconn
 USBconn +  6.60€   +  15.80€         +  10.00€    +  USBconn

So 22.40€ to talk SPI over UART over USB while the Raspberry-Pi has natively SPI, hmmm.
Bus speed view: yes there is a kind of bottleneck there...

 USBconn -- FT232RL -- MSP430F2618TPM -- MAX3420E -- USBconn
        12MB/s      115200bauds       26MHz

Let's try to make a RPi extension board with only the MAX3420E.
And to save a few cents and construction pain let's replace the USB connector by a USB cable from a cannibalized mouse.
So:

                        RPI-MODA-256M -- MAX3420E -- USBcable

From a BoM point of view this becomes (depending on which RPi, what you add to the RPi, nice casing etc):

                        RPI-MODA-256M -- MAX3420E -- USBcable
                        33.50€        +  10.00€

Bus speed view:

                        RPI-MODA-256M -- MAX3420E -- USBcable
                                      26MHz

And we get a fully autonomous facedancer which can be even powered over USB and controlled remotely

Schematics

MAX Signal RPi Signal
P3  Vcc    P17 3v3   \  0.1uF -- GND
P4  Vcc    P17 3v3   /
P5  GND    P25 GND
P6  GND    P25 GND
P10 -RES   P15 GPIO22
P11 SCLK   P23 SCLK
P12 -SS    P24 CE0
P13 MISO   P21 MISO
P14 MOSI   P19 MOSI
P15 GPX    P16 GPIO23 (currently not connected and not used)
P17 INT    P18 GPIO24 (currently not connected and not used)
P18 GND    P25 GND
P19 GND    P25 GND ---------- USB conn GND
P20 D-     ----------- R33 -- USB conn D-
P21 D+     ----------- R33 -- USB conn D+
P22 Vcc    P17 3v3  \  1uF -- GND
P23 Vcc    P17 3v3  /
P24 VBCOMP ------------------ USB conn Vcc -- 1uF -- GND
P26 XI     ------------Xtal1- 18pF -- GND
P27 XO     ------------Xtal2- 18pF -- GND

One can also connect MAX_P24 VBCOMP to RPi_P4 5V0 to power directly the RPi via this USB entry but beware:

• you're fuzzing the one which is powering you, don't cry if you experience power losses...
• the polyfuse is left out, you can re-introduce a polyfuse 1A 6V (but being powered from a *real* USB port should be fine)

Components

Name   Package Description
IC1    LQFP32  MAX3420E
R1     0603    33R USB Serie Resistor
R2     0603    33R USB Serie Resistor
C1     0603    1.0µF Capacitor
C2     0603    0.1µF Decoupling Capacitor
C3     0603    18pF Capacitor
C4     0603    18pF Capacitor
C5     0603    1.0µF Capacitor
Q1     5x3.2   12MHz SMD Crystal, 18pF      (see note)
USB    USB Mini Receptacle e.g. UX60-MB-5ST
J_RASP 2x13    Receptacle, 2.54mm, 26way    (see note)

Notes: comparing to the components reused from the original Facedancer, differences are:

• smaller crystal package
• 2x13 connector towards RPi, e.g. a SAMTEC BCS-113-L-D-TE, or even a smaller conn as 2x6 is enough, but be the sure to plug the board correctly into the larger connector!

First proto

Using a TQFP32 to DIP32 PCB adapter from http://www.ett.co.th/ and a regular through-hole crystal

Real PCB

Thanks to Jean-Christophe Nicaise for his help!
I didn't touch Eagle for so many years ^^

Jumpers & connectors:

• JP1: Jumper to get powered over USB (PoUSB)
• JP2: Solder jumper to wire INT to GPIO24 in case we'll need it
• JP3: Some pads to allow soldering directly a USB cable instead of using a USB connector
• JP4: Solder jumper to wire GPX to GPIO23 in case we'll need it
• J_RASP: Should work (except PoUSB) with a 2x6 connector instead of 2x13

Code

Travis did an amazing job at building a Python library and examples for the MAX3420E, let's reuse them!
You'll need to get GPIO Python support and SPI Python support for your Raspberry Pi.
From the original facedancer code, you'll need GoodFETMAXUSB.py and the goodfet.maxusb* scripts
Then instead of the original GoodFET.py library, use [{{#file: GoodFET.py}} this GoodFET.py version]:

#!/usr/bin/env python
# (C) 2013 Philippe Teuwen <phil at teuwen.org>

import spi
import RPi.GPIO as GPIO

class GoodFET:
    data=""
    def __init__(self, *args, **kargs):
        GPIO.setmode(GPIO.BOARD)
        # pin15=GPIO22 is linked to MAX3420E -Reset
        GPIO.setup(15, GPIO.OUT, initial=GPIO.LOW)
        GPIO.output(15,GPIO.HIGH)
        spi.openSPI(speed=26000000)
    def __del__(self):
        spi.closeSPI()
        GPIO.cleanup()
    def writecmd(self, app, verb, count=0, data=[]):
        if verb: # ignore all but R/W cmd
            return
        if isinstance(data,str):
            data = [ord(x) for x in data]
        data = tuple(data)
        data = spi.transfer(data)
        self.data = "".join([chr(x) for x in data])
    def serInit(self):
        pass

There are probably better ways to integrate it into the GoodFET software stack but with this small code snippet, you can take the latest great GoodFETMAXUSB.py and goodfet.maxusb* python scripts and just drop them along this GoodFET.py, without need for re-applying any patch.

Note that with the raspdancer, goodfet.maxusbhid is becoming too fast and I'm missing the beginning of the injected string. I had to add some initial "NoEvent / key up" chars ("\x00" * 20) in typestring() in GoodFETMAXUSB.py:

def typestring(self):
    if self.typestrings.has_key(self.OsLastConfigType):
    return ("\x00" * 20) + self.typestrings[self.OsLastConfigType];
else:
    return ("\x00" * 20) + self.typestrings[-1];