LTTO notes


Introduction

I've only had the thing 24 hours, but this is what I know so far. I'll keep this page updated as I learn more, or people send me what they have learned. If you'd like to help or have corrections, drop me a line, I'm krellboy [AT] gmail.com.

I'm not so interested in the shot protocol as I am in the muster and debrief protocols.  A stand-alone application to manage games (say, running on a palm pilot) would be a cool application.  A couple years ago I reverse engineered the LC V2 ELS protocol and wrote a similar application that runs on a PIC, but never released the code (I always just wanted to make it a little better first).

If you are interested in working on an GPL'd, Open Source project to write such an app (I'd think a palm pilot would be perfect) please drop me a line. 

Changelog:

Basic signal format

There are at least two types of signals, beacon and shot. (I haven't investigated the muster/debrief protocols much yet).  They use the same encoding but with a different preamble and word length. The longest signal I saw (including looking at the muster protocol) so far has been 8 bits, so it looks like it should be easy to stuff them into a byte.

Note: To avoid introducing silly errors in transcribing my data, I'm going to use a few arbitrary conventions that are mostly just artifacts of how things look on my logic analyzer. First is that I'm going to use active low, so a low (when on a graph) means that IR carrier is preset. Second is that I'm going to record bit streams in time, not bit significance order. IE, 011 means a zero was tranmitted first, then a 1 and another 1. Third, I'm going to call arbitrarily call "long" a 1 and a "short" and 0.

The basic signal format is a pulse width encoding. A bit time is either 3 or 4 ticks, with a tick being 1 mS. 

Here is a 0

  __
    _


Here is a 1

  __
    __


This is 101

  __  __ __
    __  _  __

The complete signal word is a preamble followed by a number of bit time slots, ie...

     6ms         
     ______      __ __ __ __ __ 
  ___      ______  _  _  _  _  _

  3ms      6ms
Which is a LTAG beacon signal.  We'll call the complete thing a 3/6/6-00000, which is the preamble timing and data bits values.

Preambles

Here are some preambles that I have seen... 

Beacon - 3/6/6


       6ms
     ______
  ___      ______


  3ms         6ms




2TMS shot - 3/9/3

       9ms
     _________
  ___         ___

  3ms         3ms



3TMS & LTAG shot - 3/6/3

      6ms
     ______
  ___      ___
  3ms      3ms




Data bits

Here are some of the data bits encountered.

Beacon: The beacon is 5 bits. So far I have only seen the first two vary. 


    TT???  - so far


values for TT (seen in 2TMS and 3TMS)

       00 - no team/individual (LTAG)
       01 - Team 1
       10 - Team 2
       11 - Team 3

values for ???
  
       000 - what I've seen so far


examples 
       01000  Team 1 player
       11000  Team 3 player
       00000  LTAG shot

Shot: A shot is 7 bits. 

    TTPPP??

The values for the TT bits are the same as in the beacon.       


values for PPP (player number - 1 as binary)


      000  Player 1
      001  Player 2
          ...
      111  Player 8


values for ??

       00 - only seen so far.  (probably one of them is mega shot)


examples

      0101000 - Team 1 Player 3
      0100100 - Team 1 Player 1
      1111100 - Team 3 Player 8

Timing

Data stream minimum bit times are 1 ms, everything is in units of 1ms.

Shots are no closer than 128ms together.

Beacons repeat every 500 (maybe 512) ms.

Muster beacon protocol looks like 3 code words 64 ms aparts.


What's next?

I'm going to make a "sniffer" to record the protocol handshakes.   Should be easy to make a decoder with a PIC and record the transactions.



Please send any corrections to krellboy {at} gmail.com