LFS Forum - OutGaugePack UDP datagram size?

#1 - PoVo

OutGaugePack UDP datagram size?

Tue, 27 Dec 2011 23:46

Hi,

I'm currently coding an OutGauge packet receiver for my Android phone in Java.

I have hit a problem where I don't know the size of the buffer in bytes for the datagram.

What's the size of the OG packet for the buffer? More importantly, how is it calculated from such detail:



<?php 
struct OutGaugePack
{
    unsigned    Time;            // time in milliseconds (to check order)

    char        Car[4];            // Car name
    word        Flags;            // Info (see OG_x below)
    byte        Gear;            // Reverse:0, Neutral:1, First:2...
    byte        PLID;            // Unique ID of viewed player (0 = none)
    float        Speed;            // M/S
    float        RPM;            // RPM
    float        Turbo;            // BAR
    float        EngTemp;        // C
    float        Fuel;            // 0 to 1
    float        OilPressure;    // BAR
    float        OilTemp;        // C
    unsigned    DashLights;        // Dash lights available (see DL_x below)
    unsigned    ShowLights;        // Dash lights currently switched on
    float        Throttle;        // 0 to 1
    float        Brake;            // 0 to 1
    float        Clutch;            // 0 to 1
    char        Display1[16];    // Usually Fuel
    char        Display2[16];    // Usually Settings

    int            ID;                // optional - only if OutGauge ID is specified
};
?>

#2 - MadCatX

Wed, 28 Dec 2011 00:14

This is actually quite easy, assuming that LFS is a 32bit x86 application. It's pretty easy to google the sizes of each variable type, x86 architecture uses



<?php 
int = 32 bits = 4 bytes
unsigned = unsigned int = 32 bits = 4 bytes
float = 32 bits = 4 bytes
double = 64 bits = 8 bytes
char = 8 bits = 1 byte
byte = unsigned char = 8 bits = 1 byte
short = 16 bits = 2 bytes
word = unsigned short = 16 bits = 2 bytes
?>

Size of an array is always SIZE_OF_TYPE * ARRAY_LENGTH, for instance the "Car" string in the OutGauge packet takes up 4 bytes. Also note that "byte" and "word" are not 'official' data types (at least not in C/C++), Scawen defined those manually to spare himself writing "unsigned short" all the time.

With this in mind, it's easy to calculate that an OutGauge packet is either 92 or 96 bytes long, it depends on whether the ID is being used.

#3 - PoVo

Wed, 28 Dec 2011 00:37

Haha just really had a dumb moment

Never thought it was a simple as that!

Thanks for clearing that up!

#4 - DarkTimes

Sun, 1 Jan 2012 00:43

You're probably going to have more trouble when you figure out that Java doesn't support unsigned integers. There is a whole open-source Java InSim library that you can steal code from (including OutGauge code), where it would seem that someone else has solved all these problems before you.

http://sourceforge.net/projects/jinsim/

#5 - MadCatX

Sun, 1 Jan 2012 01:02

The only problem I can see here is the "Time" value which could eventually exceed 2^31. I guess you could use long instead of int to work around this issue.

#6 - DarkTimes

Sun, 1 Jan 2012 02:34

Yeah, you're probably right. I was just thinking you'd need to store any byte, word or unsigned value as a different data-type (short, int and long respectively). I don't know why the makers of Java decided to do it this way, I guess it made sense at the time.