FS-T6 student cable

FS-T6 has a build in connector for another radio to be used as a trainer. However, the connector is rather unusual S-VIDEO one.  There is a discussion about making a cable in the rcgroups:
http://www.rcgroups.com/forums/showthread.php?t=1720333&page=4


The connector is on the back of the radio. It has 4 active pins and it uses connector shield for ground.  Using standard s-video (see above wikipedia link) pins the signals on the radio are:
1 - PPM TX
2 - PPM RX
3 - SERIAL TX
4 - SERIAL RX
connector ring - GND

The signals that needed to be connected between the two T6s are #1 and #2 crossed (ie TX of one radio goes to RX of another and vice-versa). I have decided to cross both PPM TX/RX and Serial TX/RX to avoid output shorts...(ie output driver another output).  Maybe one day we find a use for two radios communicating through a serial link? This essentially creates a "null modem" cable.

To make a cable you have 2 choices: 1) buy 2 plain connectors and solder the wires 2) rewire a standard s-video cable. Being a frugal guy I have opted for #2 (s-video cables are available for <$4 while single s-video connectors are more). However, standard S-VIDEO cables do not connect the grounds and connections are straight. Here, to connect two T6s you need to "cross the streams" and add the ground wire.

Start with taking out the outside rubber. I cut the connectors first, Start cutting from the cable side to the connector to avoid cable damage (if you slip the knife). Then pull the rubber off.

Next. Cut the cable in half In order to cross the streams. You may decide to do it in the middle (like I did). Or close to one of the connectors (if you want to wrap it with connector later).
After cutting, unwrapping the shields, stripping the middle wire and re-soldering crossed over, I have wrapped them in electrical insulating tape. Note, the cross over is 1<-->2 and 3<-->4 which are on different cables (connect shield of one cable to center lead of another for each cable.).

Than next I have added the ground wire. I have soldered it directly to the outside metal ring on both ends, then slipped the wire into a groove cut out in the connector plastic.

The finished cable looks rahter nagly (nasty&ugly) but it works. However, the s-video connectors do not make solid mechanical plug. So if your plugs fall out as much as mine you'd want to lead the cable through the radio handles first and then plug it in. 

My son and I flew together last week! It works!

FS-T6 and SWD hack

Preparing the FlySky-T6 RC TX for development with SWD. 

SWD = Single Wire Debug

  Well, the SWD at a minimum requires 3 wires: clock, data and ground (great marketing though).  In addition, it is very handy to add a reset line (nSRST_.  This line would reset all the devices around the core CPU in the SoC chip in addition to restarting the CPU core.  Otherwise, starting conditions would differ form run to run and I often see hangs.  I have tried to use the 3 wires (aka ST-LINK V1, as featured on STM32FVLDISCOVERY with CPU similar to the T6's stm32f1xx chip). I did not like it.  Hence later, I have hacked in the 6 pin connector.

STM32F0Discovery

Discovery

Discovery stm32f1discovery is equipped with 4 pin SWD.  All other discoveries AFAIK are ST-LINK V2 and come with 6 pin SWD.  Remove the jumpers as shown on left to disconnect the on-board SWD control from the CPU (the one that also plugs into your PC's USB; discovery docs) then you can use the SWD connector to pulg it into T6.

Notably, the V1 and V2 also differ in software. and in general the V2 is much more reliable according to openocd references.

4-pin SWD

Schematics

Here are the schematics for 4,6 pin and full 20 pin SWD connector as seen on T6.


Note that SWD lines are also used by JTAG. Through some signaling magic CPUs would cpu obey (switch into) SWD instead of JTAG.




The 4 pin is identical to the first 4 pins on 6-pin connector - handy!.

6-pin SWD

The VDO pin (pin 1 of the connectors) is not used - it is disconnected on discovery boards. I tied it to +3V3 on T6's side.

Connections to T6

T6 20-pin "full" debug connector

I have connected the following:
 U2(T6)    CN3 (DISCO)
+3.3V P1---P1 VDD 
TCK   P9---P2 TCK
GND   P20--P3 GND
TMS   P7---P4 TMS
nSRST P15--P5 NRST
GND   P18--P6 SWO

Also the SWO is not available on F1xx CPU (this is used normally for trace output). This schematics is from ar-t6 .

Here is the final result. Pin #1 is marked with a sqare, left lower row.

I have also cut out small opening for a standard 6-ping header (female) that I have crimped and than hot-glued to the case. So now I can close the T6 and have it ready for flying in no time. Additionally, I found a 12V PS with correct plug and can now power T6 on my desk w/o batteries - this is a bonus and not required.

Let me know.

...sorry for formatting - blogger is a pile of streaming google...and google really stinks recently...

Embedded software with Eclipse, Arm, Stm32fxxx, OpenOCD to develop FlySky FS-T6 trasmitter firmware

This is a very terse dump of my experience of setting up a development environment for developing software for STM32Fxxx series of ARM processors. These CPUs come in a VERY inexpensive "discovery" boards (e.g. STM32F0DISCOVERY,  STM32F3DISCOVERY, STM32F4DISCOVERY) - very fun to toy with (usually $10-20 and no need for any "emulators", "jtags" programmers etc). So this is cheaper then the famous "arduino" and you get a 32bit processor with tons of peripherals. I actually used this to start developing firmware for FlySky-T6 RC transmetter following the fantastic work here.

In order to develop embedded software one usually needs: text editor, build tools, programmer/debugger tools. Here there are in order:
- Eclipse
- gnu arb toolchain
- openocd

The Eclipse is an IDE (Integrated Development Environment) that integrates editor, project management, build, debug documentation in one common, portable, extendable GUI.

The gnu arb tool chain provides compiler/linker/stdlibraries/debugger to produce executable code.

The openocd provides access to hardware. It can communicate with hardware debugger agent and provide flash memory access and debugger server that then can interact with gdb (the gnu tools debugger). An ST-LINK/ST-UTIL (texane or STM versions) can be used instead as well.

Eclipse/GNU/OpenOCD setup

Eclipse:
http://www.eclipse.org/downloads/

this usually ends up a "java" development without CDT ("C/C++"). I have downloaded Eclipse "Luna" .
Install CDT Plugin (skip this if you've donwloaded a CDT-Eclipse):
http://www.eclipse.org/cdt/downloads.php
in the above find correct "p2 repository" link --> Copy to clipboard
in eclipse: Windows->Install New Software->Paste Link
install main CDT + GCC and HW debug
Install GNU ARM Plugin
install "p2 repository":  http://gnuarmeclipse.sourceforge.net/updates
re http://sourceforge.net/projects/gnuarmeclipse/files/Eclipse/updates
Install GCC ARM toolchain (from launchpad):
https://launchpad.net/gcc-arm-embedded/+download
setup for win32 or in debian/ubuntu apt-get install
Creating first project
select "C/C++" perspective - on the right upper, if not there "+" (add) it
file->new C/C++ project select one for your CPU; see below

WARNING - after days of somewhat working debugger I faced gradual dysfunction: 1) eclipse stopbbed being able to interract with openocd in "pipe" mode (ie when it launches oocd itself) - I have switched to running oocd manually. 2) later it decided to gray out (disable) all debug buttons even after successful start and hitting a breakpoint. This was described in this thread:
https://www.eclipse.org/forums/index.php/t/791751/. Solution was to uninstall "GDB Hardware Debug support" (the openocd pluging started to work!).

OpenOCD - Windows

Specific to the ar-t6 firmware:
Notes:
On windows you'd get 2 build errors - can't find "echo" and "make" - solution is to steal them from codesourcery as per http://gnuarmeclipse.livius.net/blog/build-tools-windows/:
http://sourceforge.net/projects/gnuarmeclipse/files/Miscellaneous/Cross%20Build%20Tools.zip/download
but an alternative would be to install gnuwin32 and add them to the path.

Based on similar w/ CodeSourcery:
http://en.radzio.dxp.pl/stm32vldiscovery/programming,with,opensource,toolchain,codesourcery,eclipse.html
http://gnuarmeclipse.livius.net/blog/openocd-install/
http://www.freddiechopin.info/en/download/category/4-openocd
usb drivers for ST-LINK:
http://www.st.com/web/catalog/tools/FM147/SC1887/PF258167
alternatively (not adviced) http://zadig.akeo.ie Options->show all->ST-LINK UpdateDriver

There may be a need to install libusb0 (can't tell if it got installed with zadig or came with ST-LINK installation). Just in case you may want to install it from here:
http://sourceforge.net/projects/libusb-win32/files/latest/download

Then in eclipse: http://gnuarmeclipse.livius.net/blog/openocd-debugging/ but it does not run openocd so had to manually run
"openocd -f stm32f0discovery.cfg -s c:\home\openocd-0.8.0\scripts"

The solution is to change to windows backslashes. Make sure the cmd params are correct as eclipse would not give you any hints as to why it failed to start it.

Other/T6 related

STM32F1xx standard peripheral library
http://www.st.com/web/catalog/tools/FM147/CL1794/SC961/SS1743/LN1734/PF257890
but no need for it as it comes with ARM plugin...

I see occasional communication problems between eclipse (gdb?) and openocd debug server. Killing the openocd process from Task Man restarts system to working condition.
git clone the ar-t6 into your "workspace" directory. the proceed to open project. If you do not know eclipse you will go through world of pain as it is not intuitive. That's okey, it will pass...

The original project builds fine with gnu tools (with some warnings about code sourcery paths) . It contains CMSIS library (arm and stm parts).

One needs to setup openocd "Debug Configuration" as per
http://gnuarmeclipse.livius.net/blog/openocd-debugging/

Also in addition I have setup a special stm32f1-fst6,cfg (saved into openocd/scripts/board)  :

# This is an FlySky T6 base on STM32F100R8
source [find interface/stlink-v2.cfg]
source [find target/stm32f1x_stlink.cfg]
# use hardware reset, connect under reset
reset_config srst_only srst_nogate

That's what goes into "config options" in the "debug" tab of debug configuration :
-f stm32f1-fst6.cfg
Try this from CLI
openocd -f stm32f1-fst6.cfg

It should report the chip id and number of hw breakpoins etc. and then wait for GDB to connect.

Also in the debug configuration that you've set up per "openocd eclipse setup" I had to change the "debug/gdb client setup/executable" to explicitly say "arm-none-eabi-gdb" as the at-t6 project does not seem to define standard "cross-" macros. The debug configuration got committed to github as "ar-t6 Debug.launch" but it's a "Windows" one.