http://www.techbricks.nl/downloads/nxtway-gyro-psp.nxc (Segway source code - 02)

//NXTway-Gyro Segway balancing robot with Hitechnic gyro
//Play station control add by Techbricks.nl using a Mindsensors PSP-Nx-v3 joystick controller 13.04.2009
//Based on JanB 20.12.2008 (NXC Bricx 3.3)
//last update 18.09.2009 - add line SetSensorHTGyro(Gyro_port) ;

//Mindsensors psp-nx PSP controller library
#include "PSP-Nx-lib.nxc"

//NXT sensor port for Mindsensors psp-nx PSP controller
const byte SensorPort  =  IN_2;
#define ADDR     0x02
/*--------------------------------------
  Controller button layout:
----------------------------------------
     l_j_x      left joystick x-axle
     l_j_y      left joystick y-axle
-------------------------------------- */
#define Gyro_port S3

//variables used for reading out PSP controller
int count=20;
int move=0, turn=0,m=0,t=0, M=0, T=0,t1=7;
psp currState;

//variables used for balaning the bot
int ng,gn=0,nw=0,rp=0,rg,lrp=0,rwi=0,md;
int GyroBiasCount,Gyro_value,GyroBias=0, batt;
long timer1;
string message, messageA, messageB;

//Read the values of the left jotstick
task psp_controller()
  {
       // Read state psp-nx PSP controller
       PSP_ReadButtonState(SensorPort, ADDR, currState);

       // read out left joystick - Y-axe
       move = (currState.l_j_y);

       // read out left joystick - X-axe
       turn =  - currState.l_j_x;

       // Display the joystick values on the NXT screen;
       message = "y:       x:          ";
       messageA = NumToStr(move);
       messageB = NumToStr(turn);
       message = StrReplace(message, 3,  messageA);
       message = StrReplace(message,12 , messageB);
       TextOut(0, LCD_LINE7, message, false);

       //return the values to the bot balancing task
       m=move / 16;       //devide joystick y-axe by factor
       t=turn / 5;        //devide joystick x-axe by factor

       // During the psp_controller task, statements of the balancing task are executed slower.
       // The processor of the NXT is serving 2 tasks at the same time after all.
       // Therefore, end the end of the psp_comtroller task, the cuclus delay is set back from 4 ms to 7 ms.
       t1=7;              //set cyclus delay back to 7 ms
     }
task balansing()
  {
  while(true)
   {
     ng=SensorRaw(S3)-gn; nw+=ng;  //body angle in radians/sec
     rp=(MotorTachoCount(OUT_A)+MotorTachoCount(OUT_B))/2;    //wheel position
     M = (M*75+m*25)/100;          //To let the bot lowly get used to the for- and backward movements
     rg=rp-lrp; lrp=rp; rwi+=rg-M; //wheel speed + joystick forward value
     if (abs(rwi)>15){gn-=sign(rwi); rwi=0;} //Gyro drift compensation.
     md=(nw+ng*10+rp*4+rg*200)>>4; //pd contr. NXT small wheels
  // md=(nw+ng*12+rp*5+rg*360)>>5; //pd contr. RXC large wheels
     md+=sign(md)*48;              //friction compensation   default = 48
     SetOutput(OUT_A,              //PID motor control motor A
               Power,
               md-t,               //balance correction - joystick turn value.
               OutputMode,
               OUT_MODE_MOTORON,
               RunState,
               OUT_RUNSTATE_RUNNING,
               UpdateFlags,
               UF_UPDATE_MODE+UF_UPDATE_SPEED);
     SetOutput(OUT_B,              //PID motor control motor A
               Power,
               md+t,               //balance correction + joystick turn value.
               OutputMode,
               OUT_MODE_MOTORON,
               RunState,
               OUT_RUNSTATE_RUNNING,
               UpdateFlags,
               UF_UPDATE_MODE+UF_UPDATE_SPEED);
     if (count==20)                //ones in 20 cycles (= 5 times per second)
        {
          count=0;
          // During the task psp_controller the balancing task runs slower.
          // Therefore the cuclus delay is set from 7 ms to 4 ms.
          t1=4;                     // set cyclus delay to 4 ms
          StartTask(psp_controller);// get joystick values m & t
        }
          count+=1;
      Wait(t1);                     //Delay to slow down the loop to about 100 times/sec (default = 7ms)
    }
  }


task main(){
   //set RAW_MODE Gyro sensor port
     SetSensorHTGyro(Gyro_port) ;
   // Calculate the Giro Bias for the Hitechnic Gyro sensor.
   // by measuring the Gyro value many times in 3 secondes.
   // Gyro Bias is avarage Gyro value: Sum of values devide by time measured.
   timer1 = CurrentTick();  // set timer1
   GyroBiasCount = 0;
   while (CurrentTick() < (3000+timer1)) {
	  	// filter the sensor output
      Gyro_value = SensorRaw(S3);
      Wait(150);
      GyroBiasCount = GyroBiasCount + 1;
 		  gn = gn + Gyro_value;
 		  PlayTone(TONE_B7, 5);
   }
   GyroBias = gn / GyroBiasCount; //Sum of values devide by time measured.
   gn=GyroBias;

   // Measure the battery voltage.
   batt=BatteryLevel();

   // Display calculated GyroBias an battery voltage on the NXT screen;
   message = "Gbias    Bat          ";
   messageA = NumToStr(gn);
   messageB = NumToStr(batt);
   message = StrReplace(message, 5,  messageA);
   message = StrReplace(message, 12, messageB);
   TextOut(0, LCD_LINE1, message, false);

   //calculating GyroBias completed!
   PlayTone(TONE_B7, 100);

   //start self balansing task
   Precedes(balansing);
}
//end