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Inspired by Jordi's blog I tried to receive the serial data from a (pre-bound) SPM9645 remote receiver with RPi's GPIO. Maybe this information can be useful to you or it can save you some time. I am happy for some feedback or optimization proposals etc.

The following RPi GPIO Pins are used (*):

• [P1-01]  3.3V
• [P1-06]  GROUND
• [P1-10]  GPIO 15 (RXD)

Before you can use RPi's serial interface /dev/ttyAMA0 to read the data you need to make sure that there is no serial console or kernel debug function that uses the interface.

Remove the following options from your /boot/cmdline.txt:

console=ttyAMA0,115200 kgdboc=ttyAMA0,115200

Remove the following line from your /etc/inittab:

T0:23:respawn:/sbin/getty -L ttyAMA0 115200 vt100

Reboot the device and make sure you switched on your Spektrum transmitter (DX6i).

It should now be possible to read the SPM9645 serial data from the serial interface /dev/ttyAMA0:

Python 2.7.3 (default, Jan 13 2013, 11:20:46)

[GCC 4.6.3] on linux2

Type "help", "copyright", "credits" or "license" for more information.

>>> import serial

>>> from struct import *

>>> port = serial.Serial('/dev/ttyAMA0', baudrate=115200, timeout=3.0)

>>> print unpack('>xxhhhhhhh', port.read(16))

Have fun and stay tuned.

References:

• 2.4ghz: How to read 7 channels with one wire (NOT PPM) with Spektrum modules
• Spektrum DSMX Remote Receiver
• RPi Low-level peripherals
• pySerial

Notes:

It does not seem to be possible to use the suggested baudrate of 125000.

(* of course you can use any other 3.3V or GROUND Pin)