APM2 Serial3/UART2 not functional

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What steps will reproduce the problem?
1.Power on AP2
2.Set SERIAL3_BAUD and SR3_PARAMS
3.monitor UART2 pins (long side of board or UART0/2 if soldered) 

What is the expected output? Data What do you see instead? nothing

What version of the product are you using? On what operating system?

arducopter 2.5.5, MP 1.1.92, X-CTU, arduino relax-patch

Please provide any additional information below.
After testing without success I uploaded simple arduino sketch that prints port 
specific text to each serial port except serial1 (GPS). 

What I found was I was able to test Serial0 (USB) sucessfully
read Serial1 (GPS) 38400baud successfully
read Serial2 (UART2) successfully
Serial3 i'm not sure where the connection is on the APM2 if any.

The problem lies that all the documentation and I believe the code assumes 
Serial3=UART2 which in my test is shown to be false?

Original issue reported on code.google.com by TuxI...@gmail.com on 13 Jun 2012 at 12:59

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I'M not an original APM1 owner to confirm, but it seems likely that the APM1 
used Serial2 tied to a pinout labeled UART3. It seems that also that the 
general documentation and practice was just adopted into the APM2 wiki. 

I did more testing on APM2 Serial2 using the UserCode space in arducopter 2.5.5 
and its 100%a clear that Serial2 is tied to UART2 pins on the APM2 board. Where 
the connection (if available) for Seria3/UART3 is located on the board I'm 
still not sure.

As a major component both hardware and software side, can we get this issue 
prioritized?

I would be more than happy to participate however needed to 
test/confirm/resolve the issue.

As a temporary work-around I wonder if its possible to simply re-route serial3 
data to serial2?

Original comment by TuxI...@gmail.com on 14 Jun 2012 at 11:22

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Has any attempt been made to resolve this issue? In the Arduplane code it seems 
Serial3=Serial2, somehow, somewhere. If I replace Serial3 with Serial2 in the 
main ArduPlane.pde serial port configuration section, compile time errors occur:

////////////////////////////////////////////////////////////////////////////////
// Serial ports
////////////////////////////////////////////////////////////////////////////////
//
// Note that FastSerial port buffers are allocated at ::begin time,
// so there is not much of a penalty to defining ports that we don't
// use.
//
FastSerialPort0(Serial);        // FTDI/console
FastSerialPort1(Serial1);       // GPS port
#if TELEMETRY_UART2 == ENABLED
 // solder bridge set to enable UART2 instead of USB MUX
 FastSerialPort2(Serial3);
#else
 FastSerialPort3(Serial3);       // Telemetry port for APM1
#endif

In ArduPlane code, it is not well documented that the config.h file must be 
changed to set TELEMETRY_UART2 to "ENABLED" instead of "DISABLED" and add the 
following code to the serial port speeds section to get telemetry functional on 
UART2 after performing the solder bridge modification:

//Start CTSi code
#ifndef SERIAL2_BAUD
# define SERIAL2_BAUD            57600
#endif
//End CTSi code

Hopefully this issue can be solved properly (replace serial3 with serial2) 
and/or better documentation added to the wiki.

Original comment by samc9...@gmail.com on 2 Aug 2012 at 3:52

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Sam, I have tried my best as I am not much of an arduino programmer. I tried 
hours of compiling changes to the code which compiled ok just no data from 
serial2. I tried to redirect in userspace also which failed as I have no 
complete understanding of the fastserial library. I called several times to 
speak with 3dr and all I could get was an agreement that it is firmware related.

Original comment by TuxI...@gmail.com on 3 Aug 2012 at 2:54

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I also have just stumbled upon this issue. After hours of thinking I had my 
XTEND set up incorrectly, I decided to modify the MultiSerialMega sketch to 
send data out on all serial ports, and that helped me figure out that it was 
the APM code itself that was not correct.
I will look through the code and see if I can fix this.

Original comment by mswil...@mtu.edu on 8 Sep 2012 at 12:24

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After going over the schematic for APM2.5.1 I can confirm that Serial3 connects 
to dataflash. Made changes to the code so far to test things, but having 
compilation problems -_-;

Original comment by mswil...@mtu.edu on 8 Sep 2012 at 2:59

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S0=USB
S1=GPS
S2=optical flow? I recall seeing this in various web sources. Unconfirmed.
S3=data flash confirmed by last member. 

If the above is complete and true then there simply isn't a dedicated telemetry 
port. 

Perhaps they simply incorporated apm1 wiki documentation and firmare code into 
apm2 documentation. I find it rather convient that the 3dr radio setup piggy 
backs USB serial0. This also seemes to be the community workaround for xbee or 
other hardware. This also leaves us with near zero user configurability. This 
is much less less we might have been mislead by the documentation. :(          

Original comment by TuxI...@gmail.com on 8 Sep 2012 at 3:42

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S2=Radio
Optical flow sensor is on the SPI bus I do believe (the 2x3 pin header next to 
the USB port on APM2.5.1)

Original comment by mswil...@mtu.edu on 10 Sep 2012 at 4:48