File content as of revision 0:ee7076d8260a:

// Code based on Carlos E. Vidales tutorial : How To Calibrate Touch Screens
// http://www.embedded.com/design/configurable-systems/4023968/How-To-Calibrate-Touch-Screens

#include "Touch.h"
#include "mbed.h"
#include "Arial12x12.h"

// (To be modified) C code below works on KEIL compiler but NOT on LPCXpresso/mbed 
//Matrix matrix ;
//Coordinate  display ;

Coordinate ScreenSample[3] =   {
        { 45, 45 },
        { 45, 270},
        { 190,190}
} ;
Coordinate DisplaySample[3] =   {
        { 45, 45 },
        { 45, 270},
        { 190,190}
} ;

#define THRESHOLD 2
// **********************************************************************

TouchScreenADS7843::TouchScreenADS7843(PinName tp_mosi,PinName tp_miso,PinName tp_sclk,PinName tp_cs,PinName tp_irq,PinName mosi, PinName miso, PinName sclk, PinName cs, PinName reset,const char* name)
        : _tp_spi(tp_mosi, tp_miso, tp_sclk), _tp_cs(tp_cs), _tp_irq(tp_irq),SPI_TFT(mosi,miso,sclk,cs,reset,name) {}
// **********************************************************************
void TouchScreenADS7843::TP_Init(void)
{
    _tp_cs=1;
    _tp_spi.frequency(500000);
       _tp_spi.format(8,0);                    // 8 bit spi mode 3
}

int TouchScreenADS7843::Read_XY(unsigned char XY)
{
    unsigned char msb, lsb;
    unsigned int Temp;

    Temp=0;
    _tp_cs=0;
    wait_us(SPI_RD_DELAY);
    _tp_spi.write(XY);
    wait_us(SPI_RD_DELAY);
    msb = _tp_spi.write(0x00); // msb
    wait_us(SPI_RD_DELAY);
    lsb = _tp_spi.write(0x00); // lsb
    _tp_cs=1;
    Temp = ((msb <<8 ) | lsb);
    Temp >>= 3;
    Temp &= 0xfff;
    Temp /= 4;        // Scaling : return value range must be between 0 and 1024
//    Temp = (((msb & 0x7f) <<8) | lsb) >> 3;        // 12 bit
    return(Temp);
}


void TouchScreenADS7843::TP_GetAdXY(int *x,int *y)
{
    int adx,ady;
    adx = Read_XY(CHX);
    wait_us(1);
    ady = Read_XY(CHY);
    *x = adx;
    *y = ady;
}

void TouchScreenADS7843::TP_DrawPoint(unsigned int Xpos,unsigned int Ypos, unsigned int color)
{
    wr_reg(0x03, 0x1030);
    WindowMax();
    pixel(Xpos,Ypos,color);
    pixel(Xpos+1,Ypos,color);
    pixel(Xpos,Ypos+1,color);
    pixel(Xpos+1,Ypos+1,color);
}

void TouchScreenADS7843::DrawCross(unsigned int Xpos,unsigned int Ypos)
{
    line(Xpos-15,Ypos,Xpos-2,Ypos,White);
    line(Xpos+2,Ypos,Xpos+15,Ypos,White);
    line(Xpos,Ypos-15,Xpos,Ypos-2,White);
    line(Xpos,Ypos+2,Xpos,Ypos+15,White);

    line(Xpos-15,Ypos+15,Xpos-7,Ypos+15,DarkGrey);
    line(Xpos-15,Ypos+7,Xpos-15,Ypos+15,DarkGrey);

    line(Xpos-15,Ypos-15,Xpos-7,Ypos-15,DarkGrey);
    line(Xpos-15,Ypos-7,Xpos-15,Ypos-15,DarkGrey);

    line(Xpos+7,Ypos+15,Xpos+15,Ypos+15,DarkGrey);
    line(Xpos+15,Ypos+7,Xpos+15,Ypos+15,DarkGrey);

    line(Xpos+7,Ypos-15,Xpos+15,Ypos-15,DarkGrey);
    line(Xpos+15,Ypos-15,Xpos+15,Ypos-7,DarkGrey);
}

unsigned char TouchScreenADS7843::Read_Ads7846(Coordinate * screenPtr)
{
//    static Coordinate  screen;
    int m0,m1,m2,TP_X[1],TP_Y[1],temp[3];
    uint8_t count=0;
    int buffer[2][9]={{0},{0}};
    do
    {
        TP_GetAdXY(TP_X,TP_Y);
        buffer[0][count]=TP_X[0];
        buffer[1][count]=TP_Y[0];
        count++;
    }
    while(!_tp_irq && (count < 9));
    if(count==9)
    {
        temp[0]=(buffer[0][0]+buffer[0][1]+buffer[0][2])/3;
        temp[1]=(buffer[0][3]+buffer[0][4]+buffer[0][5])/3;
        temp[2]=(buffer[0][6]+buffer[0][7]+buffer[0][8])/3;
        m0=temp[0]-temp[1];
        m1=temp[1]-temp[2];
        m2=temp[2]-temp[0];
        m0=m0>0?m0:(-m0);
        m1=m1>0?m1:(-m1);
        m2=m2>0?m2:(-m2);
        if( (m0>THRESHOLD)  &&  (m1>THRESHOLD)  &&  (m2>THRESHOLD) ) return 0;
        if(m0<m1)
        {
            if(m2<m0)
                screenPtr->x=(temp[0]+temp[2])/2;
            else
                screenPtr->x=(temp[0]+temp[1])/2;
        }
        else if(m2<m1)
            screenPtr->x=(temp[0]+temp[2])/2;
        else
            screenPtr->x=(temp[1]+temp[2])/2;

        temp[0]=(buffer[1][0]+buffer[1][1]+buffer[1][2])/3;
        temp[1]=(buffer[1][3]+buffer[1][4]+buffer[1][5])/3;
        temp[2]=(buffer[1][6]+buffer[1][7]+buffer[1][8])/3;
        m0=temp[0]-temp[1];
        m1=temp[1]-temp[2];
        m2=temp[2]-temp[0];
        m0=m0>0?m0:(-m0);
        m1=m1>0?m1:(-m1);
        m2=m2>0?m2:(-m2);
        if( (m0>THRESHOLD)  &&  (m1>THRESHOLD)  &&  (m2>THRESHOLD) ) return 0;

        if(m0<m1)
        {
            if(m2<m0)
                screenPtr->y=(temp[0]+temp[2])/2;
            else
                screenPtr->y=(temp[0]+temp[1])/2;
        }
        else if(m2<m1)
            screenPtr->y=(temp[0]+temp[2])/2;
        else
            screenPtr->y=(temp[1]+temp[2])/2;
        return 1;
    }
    return 0;
}

uint8_t TouchScreenADS7843::setCalibrationMatrix( Coordinate * displayPtr,
        Coordinate * screenPtr,
        Matrix * matrixPtr)
{
    uint8_t retTHRESHOLD = 0 ;
    // K = (Xs0 - Xs2)*(Ys1 - Ys2) - (Xs1 - Xs2)*(Ys0 - Ys2)
    matrixPtr->Divider = ((screenPtr[0].x - screenPtr[2].x) * (screenPtr[1].y - screenPtr[2].y)) -
                         ((screenPtr[1].x - screenPtr[2].x) * (screenPtr[0].y - screenPtr[2].y)) ;
    if( matrixPtr->Divider == 0 )
    {
        retTHRESHOLD = 1;
    }
    else
    {
        //                 (Xd0 - Xd2)*(Ys1 - Ys2) - (Xd1 - Xd2)*(Ys0 - Ys2)
        //            A = ---------------------------------------------------
        //                                   K
        matrixPtr->An = ((displayPtr[0].x - displayPtr[2].x) * (screenPtr[1].y - screenPtr[2].y)) -
                          ((displayPtr[1].x - displayPtr[2].x) * (screenPtr[0].y - screenPtr[2].y)) ;
        //                 (Xs0 - Xs2)*(Xd1 - Xd2) - (Xd0 - Xd2)*(Xs1 - Xs2)
        //            B = ---------------------------------------------------
        //                                   K
        matrixPtr->Bn = ((screenPtr[0].x - screenPtr[2].x) * (displayPtr[1].x - displayPtr[2].x)) -
                        ((displayPtr[0].x - displayPtr[2].x) * (screenPtr[1].x - screenPtr[2].x)) ;
        //                 Ys0*(Xs2*Xd1 - Xs1*Xd2) + Ys1*(Xs0*Xd2 - Xs2*Xd0) + Ys2*(Xs1*Xd0 - Xs0*Xd1)
        //            C = ----------------------------------------------------------------------------
        //                                   K
        matrixPtr->Cn = (screenPtr[2].x * displayPtr[1].x - screenPtr[1].x * displayPtr[2].x) * screenPtr[0].y +
                        (screenPtr[0].x * displayPtr[2].x - screenPtr[2].x * displayPtr[0].x) * screenPtr[1].y +
                        (screenPtr[1].x * displayPtr[0].x - screenPtr[0].x * displayPtr[1].x) * screenPtr[2].y ;
        //                 (Yd0 - Yd2)*(Ys1 - Ys2) - (Yd1 - Yd2)*(Ys0 - Ys2)
        //            D = ---------------------------------------------------
        //                                   K
        matrixPtr->Dn = ((displayPtr[0].y - displayPtr[2].y) * (screenPtr[1].y - screenPtr[2].y)) -
                        ((displayPtr[1].y - displayPtr[2].y) * (screenPtr[0].y - screenPtr[2].y)) ;
        //                 (Xs0 - Xs2)*(Yd1 - Yd2) - (Yd0 - Yd2)*(Xs1 - Xs2)
        //            E = ---------------------------------------------------
        //                                   K
        matrixPtr->En = ((screenPtr[0].x - screenPtr[2].x) * (displayPtr[1].y - displayPtr[2].y)) -
                        ((displayPtr[0].y - displayPtr[2].y) * (screenPtr[1].x - screenPtr[2].x)) ;
        //                 Ys0*(Xs2*Yd1 - Xs1*Yd2) + Ys1*(Xs0*Yd2 - Xs2*Yd0) + Ys2*(Xs1*Yd0 - Xs0*Yd1)
        //            F = ----------------------------------------------------------------------------
        //                                   K
        matrixPtr->Fn = (screenPtr[2].x * displayPtr[1].y - screenPtr[1].x * displayPtr[2].y) * screenPtr[0].y +
                        (screenPtr[0].x * displayPtr[2].y - screenPtr[2].x * displayPtr[0].y) * screenPtr[1].y +
                        (screenPtr[1].x * displayPtr[0].y - screenPtr[0].x * displayPtr[1].y) * screenPtr[2].y ;
    }
    return( retTHRESHOLD ) ;
}

uint8_t TouchScreenADS7843::getDisplayPoint(Coordinate *displayPtr,
        Coordinate *screenPtr,
        Matrix *matrixPtr )
{
    uint8_t retTHRESHOLD = 0 ;

    if( matrixPtr->Divider != 0 )
    {
        // XD = AX+BY+C
        displayPtr->x = ( (matrixPtr->An * screenPtr->x) +
                          (matrixPtr->Bn * screenPtr->y) +
                           matrixPtr->Cn
                         ) / matrixPtr->Divider ;
        // YD = DX+EY+F
        displayPtr->y = ( (matrixPtr->Dn * screenPtr->x) +
                          (matrixPtr->En * screenPtr->y) +
                           matrixPtr->Fn
                         ) / matrixPtr->Divider ;
    }
    else
    {
        retTHRESHOLD = 1;
    }
    return(retTHRESHOLD);
}

void TouchScreenADS7843::TouchPanel_Calibrate(Matrix *matrixPtr)
{
    uint8_t i;
    Coordinate screen_cal;
    setCalibrationMatrix( &DisplaySample[0],&ScreenSample[0],matrixPtr ) ;
    set_font((unsigned char*) Arial12x12);
    for(i=0;i<3;i++)
    {
        cls();
        locate(10,10);
        printf("Touch crosshair to calibrate");
        wait_ms(500);
        DrawCross(DisplaySample[i].x,DisplaySample[i].y);
        do {} while (!Read_Ads7846(&screen_cal));
        ScreenSample[i].x= screen_cal.x; ScreenSample[i].y= screen_cal.y;
    }
    setCalibrationMatrix( &DisplaySample[0],&ScreenSample[0],matrixPtr ) ;
    cls();
}