File content as of revision 1:f167423f6f0c:

/**
@file main.cpp
@brief Electronic Angle Meter and Spirit Level.
@brief Revision 1.0.
@author Shengyuan Chu
@date May 2015
*/

#include "mbed.h"
#include "main.h"
#include "MMA8452.h"
#include "PowerControl/PowerControl.h"
#include "PowerControl/EthernetPowerControl.h"

/**
@brief Connect all components to mbed LPC1768.
@brief Connect LCD to pin 7,8,9,10,11,13,26.
@brief Connect Accelerometer to pin 27,28.
@brief Connect buzzer to pin 21.
@brief Connect button to pin 17.
@brief Connect LEDs to pin 22,23,24,25.
*/
N5110 lcd(p7,p8,p9,p10,p11,p13,p26);
MMA8452 mma8452(p28,p27);
PwmOut buzzer(p21);
DigitalIn pb(p17);                
DigitalOut ledA(p25);
DigitalOut ledB(p23);
DigitalOut ledC(p22);
DigitalOut ledD(p24);

Serial serial(USBTX,USBRX);
Timeout flipper;

/**
@brief Function prototypes.
*/
void Switch (int functoion);           
void AngleMeter();
void SpiritLevel();
void fun1();
void fun2();

/**
@brief Different frequencies of buzzer.
*/
float frequency1 = 1046.5;
float frequency2 = 1174.7;
float frequency3 = 1318.5;

/**
@brief Main function.
@brief Call function of Angle Meter without pushing 
@brief button when power is initally turned on.
*/
int main() {
    
    /**Power down Ethernet interface to save power.*/    
    PHY_PowerDown();
    
    /**Initialise LCD and set brightness to 0.8.*/ 
    lcd.init();
    lcd.normalMode();    
    lcd.setBrightness(0.8);
    
    /**Display the name of Angle Meter function after the initialization of LCD.*/ 
    lcd.printString("Electronic",12,2);
    lcd.printString("Angle Meter",10,3);
    
    /**Call function of Angle Meter after 2 seconds' delay.*/ 
    flipper.attach(&AngleMeter, 2.0);
        
    /**Turn all the LEDs on when the power is initially turned on.*/ 
    ledA=1;
    ledB=1;
    ledC=1;
    ledD=1;
    
    /**Set button to PullDown mode.*/           
    pb.mode(PullDown);           
 
    /**Change the integer between 1 and 2 when button is pressed and send it to Switch function.*/
    int function = 1;        
    
    while(1) {
        if (pb){                 
            Switch(function); 
            
            /**Allow 0.2 second for button debounce.*/          
            wait(0.2);             
            while (pb);          
            {if (function == 2) function = 1; else function++;} 
        }        
    }   
}

/**
@brief Switch functions between Angle Meter and Spirit Level.
@param function - integer to change between 1 and 2.
@return Call fun1() when function=2, call fun2() when function=1.
*/   
void Switch (int function) 
{         
    
    switch (function) {
        case 1 : fun2(); 
        break;
        case 2 : fun1(); 
        break;
    }
    
}

 /**
 @brief Display angles in two dimensions and indicate directions using arrows.
 */
void AngleMeter() 
{    
    /**Initialise the accelerometer.*/       
    mma8452.init();
    Acceleration acceleration; 
    
    /**Lower down the brightness of LCD to 0.5.*/ 
    lcd.clear();
    lcd.setBrightness(0.5); 
    
    /**When button is not pushed, main features of Angle Meter will be run.*/ 
    while(!pb) {
        
        /**Display 'degree' in the last line of LCD.*/      
        lcd.printString("degree",3,5);
        lcd.printString("degree",46,5);
        
        /**Read value of acceleration.*/
        acceleration = mma8452.readValues();
    
        float X=acceleration.x;
        float Y=acceleration.y;
        float Z=acceleration.z;
        
        /**Calculate the angles in X and Y dimensions.*/
        float Ax=atan(X/sqrt(pow(Y,2)+pow(Z,2)))/3.14159265358979323846*180;
        float Ay=atan(Y/sqrt(pow(X,2)+pow(Z,2)))/3.14159265358979323846*180;
        
        /**Print formatted data to buffer.*/
        char buffer1[14]; 
        int length = sprintf(buffer1,"%.0f",abs(Ax));
        char buffer2[14]; 
        length = sprintf(buffer2,"%.0f",abs(Ay)); 
   
        /**Display values if string will fit on display.*/
        if (length <= 14)  // 
            lcd.printString(buffer1,20,3); 
            lcd.printString(buffer2,55,3);      
        
        /**LED C will be turned on if the angle in X dimension is larger than 20 degree.*/
        if (Ax>20)
            ledC=1;
        else
            ledC=0;
        
        /**LED A will be turned on if the angle in X dimension is smaller than -20 degree.*/
        if (Ax<-20)
            ledA=1;
        else
            ledA=0;
        
        /**LED D will be turned on if the angle in Y dimension is larger than 20 degree.*/ 
        if (Ay>20)
            ledD=1;
        else
            ledD=0;
        
        /**LED B will be turned on if the angle in Y dimension is smaller than -20 degree.*/
        if (Ay<-20)
            ledB=1;
        else
            ledB=0;
         
        /**Draw lines of the body of arrows.*/ 
        lcd.drawLine(58,6,58,16,1);
        lcd.drawLine(17,11,29,11,1);
        lcd.refresh();     
        
        /**Pixes will be set if the angle in Y dimension is larger than 0 degree.*/             
        if (Ay>=0){
            lcd.setPixel(60,5);
            lcd.setPixel(59,5);
            lcd.setPixel(58,5);
            lcd.setPixel(57,5);
            lcd.setPixel(56,5);
            lcd.setPixel(59,4);
            lcd.setPixel(58,4);
            lcd.setPixel(57,4);
            lcd.setPixel(58,3);
            lcd.refresh(); 
        }
        
        /**Pixes will be set if the angle in Y dimension is smaller than 0 degree.*/     
        else if (Ay<=0) {
            lcd.setPixel(60,17);
            lcd.setPixel(59,17);
            lcd.setPixel(58,17);
            lcd.setPixel(57,17);
            lcd.setPixel(56,17);
            lcd.setPixel(59,18);
            lcd.setPixel(58,18);
            lcd.setPixel(57,18);
            lcd.setPixel(58,19);
            lcd.refresh(); 
        }
        
        /**Pixes will be set if the angle in X dimension is larger than 0 degree.*/ 
        if (Ax>=0) {
            lcd.setPixel(30,13);
            lcd.setPixel(30,12);
            lcd.setPixel(30,11);
            lcd.setPixel(30,10);
            lcd.setPixel(30,9);
            lcd.setPixel(31,12);
            lcd.setPixel(31,11);
            lcd.setPixel(31,10);
            lcd.setPixel(32,11);
            lcd.refresh(); 
        }
        
        /**Pixes will be set if the angle in X dimension is smaller than 0 degree.*/     
        else if (Ax<=0) {
            lcd.setPixel(16,13);
            lcd.setPixel(16,12);
            lcd.setPixel(16,11);
            lcd.setPixel(16,10);
            lcd.setPixel(16,9);
            lcd.setPixel(15,12);
            lcd.setPixel(15,11);
            lcd.setPixel(15,10);
            lcd.setPixel(14,11);
            lcd.refresh(); 
        }
        
        /**Decrease the fluctuation of values.*/     
        wait(0.3);
        lcd.clear();
        
        /**Buzzer will beep in frequency 2 if the angle is between 50 and 75 degree.*/ 
        if ((abs(Ax) >= 50 && abs(Ax) < 75)||(abs(Ay) >= 50 && abs(Ay) < 75)) {
            buzzer.period(1/frequency2);
            buzzer=0.1;
        }  
        
        /**Buzzer will beep in frequency 3 if the angle is beyond 75 degree.*/            
        else if ((abs(Ax) >= 75)||(abs(Ay) >= 75)) {
            buzzer.period(1/frequency3);
            buzzer=0.1;
        }  
        
        /**Buzzer will not beep.*/
        else {
            buzzer.period(1/frequency1);
            buzzer=0;
        }         
    }     
    
    /**When button is pushed, main features will stop.*/
    while(pb) {
        break;
    }    
}
     
/**
@brief Indicate the gradient in all directions by showing
@brief the position of a group of pixes.
*/
void SpiritLevel()
{
    /**Initialise all the LEDs to be off.*/  
    ledA=0;
    ledB=0;
    ledC=0;
    ledD=0; 

    /**Set the LCD to inverse mode and lower down the brightness to 0.5.*/     
    lcd.clear();
    lcd.inverseMode(); 
    lcd.setBrightness(0.5);
    
    /**Initialise the accelerometer.*/      
    mma8452.init();    
    Acceleration acceleration; 

    /**When button is not pushed, main features of Spirit Level will be run.*/       
    while(!pb) {        
        
        /**Read value of acceleration.*/
        acceleration = mma8452.readValues();//read value of acceleration
        
        float Ax=acceleration.x;
        float Ay=acceleration.y;

        /**Draw three circles and two lines.*/
        lcd.drawCircle(41,24,23,0);
        lcd.drawCircle(41,24,4,0);
        lcd.drawCircle(41,24,13,0);
        lcd.drawLine(41,3,41,45,1);
        lcd.drawLine(20,24,62,24,1);       
        lcd.refresh();
    
        /**Pixes will be displayed if acceleration values are within -0.4 and 0.4.*/
        if (abs(Ax)<=0.4&&abs(Ay)<=0.4) {
     
            float X=Ax/0.018;
            float Y=Ay/0.018;
            
            lcd.setPixel(42+X, 26-Y);
            lcd.setPixel(41+X, 26-Y);
            lcd.setPixel(40+X, 26-Y);
            lcd.setPixel(43+X, 25-Y);
            lcd.setPixel(42+X, 25-Y);
            lcd.setPixel(41+X, 25-Y);
            lcd.setPixel(40+X, 25-Y);
            lcd.setPixel(39+X, 25-Y);
            lcd.setPixel(43+X, 24-Y);
            lcd.setPixel(42+X, 24-Y);
            lcd.setPixel(41+X, 24-Y);
            lcd.setPixel(40+X, 24-Y);
            lcd.setPixel(39+X, 24-Y);
            lcd.setPixel(43+X, 23-Y);
            lcd.setPixel(42+X, 23-Y);
            lcd.setPixel(41+X, 23-Y);
            lcd.setPixel(40+X, 23-Y);
            lcd.setPixel(39+X, 23-Y);
            lcd.setPixel(42+X, 22-Y);
            lcd.setPixel(41+X, 22-Y);
            lcd.setPixel(40+X, 22-Y);
            lcd.refresh();
            
            /**Displayed pixes will be cleared after 0.2 second.*/
            wait(0.2);
 
            lcd.clearPixel(42+X, 26-Y);
            lcd.clearPixel(41+X, 26-Y);
            lcd.clearPixel(40+X, 26-Y);    
            lcd.clearPixel(43+X, 25-Y);    
            lcd.clearPixel(42+X, 25-Y);
            lcd.clearPixel(41+X, 25-Y);
            lcd.clearPixel(40+X, 25-Y);
            lcd.clearPixel(39+X, 25-Y);
            lcd.clearPixel(43+X, 24-Y);    
            lcd.clearPixel(42+X, 24-Y);
            lcd.clearPixel(41+X, 24-Y);
            lcd.clearPixel(40+X, 24-Y);
            lcd.clearPixel(39+X, 24-Y);
            lcd.clearPixel(43+X, 23-Y);    
            lcd.clearPixel(42+X, 23-Y);
            lcd.clearPixel(41+X, 23-Y);
            lcd.clearPixel(40+X, 23-Y);
            lcd.clearPixel(39+X, 23-Y);
            lcd.clearPixel(42+X, 22-Y);
            lcd.clearPixel(41+X, 22-Y);
            lcd.clearPixel(40+X, 22-Y);
            lcd.refresh();    
        }
     
        /**All LEDs will be turned on if acceleration values are within -0.05 and 0.05.*/
        if (abs(Ax)<=0.05&&abs(Ay)<=0.05) {   
            ledA=1;
            ledB=1;
            ledC=1;
            ledD=1; 
        }
      
        /**All LEDs will be turned off if acceleration values go beyond this range.*/
        else {
            ledA=0;
            ledB=0;
            ledC=0;
            ledD=0; 
        }
    }
}
        
/**
@brief Display the function name of Angle Meter for 1 second before calling it.
*/     
void fun1() 
{   
    /**Initialise the LCD and set brightness to 0.8.*/   
    lcd.init();
    lcd.normalMode();   
    lcd.setBrightness(0.8);
    lcd.clear();
    
    /**Display the function name of Angle Meter.*/   
    lcd.printString("Electronic",12,2);
    lcd.printString("Angle Meter",10,3);
    
    /**Turn LED A and LED C on.*/   
    ledA=1;
    ledB=0;
    ledC=1;
    ledD=0;
     
    /**Call function of Angle Meter after 1 second delay.*/      
    flipper.attach(&AngleMeter, 1.0);      
}

/**
@brief Display the function name of Spirit Level for 1 second before calling it.
*/          
void fun2()
{
    /**Turn off the buzzer.*/   
    buzzer = 0;
    
    /**Initialise the LCD and set brightness to 0.8.*/   
    lcd.init();
    lcd.normalMode();    
    lcd.setBrightness(0.8);
    lcd.clear();
    
    /**Display the function name of Spirit Level.*/     
    lcd.printString("Electronic",12,2);
    lcd.printString("Spirit Level",7,3);

    /**Turn LED B and LED D on.*/                 
    ledA=0;
    ledB=1;
    ledC=0;
    ledD=1;

    /**Call function of Spirit Level after 1 second delay.*/           
    flipper.attach(&SpiritLevel, 1.0);       
}

/**
@brief Power down the Ethernet interface to save power.
@brief Acknowledgements to Michael Wei's code.
*/
void PHY_PowerDown()
{
    if (!Peripheral_GetStatus(LPC1768_PCONP_PCENET))
        EMAC_Init(); //init EMAC if it is not already init'd
    
    unsigned int regv;
    regv = read_PHY(PHY_REG_BMCR);
    write_PHY(PHY_REG_BMCR, regv | (1 << PHY_REG_BMCR_POWERDOWN));
    regv = read_PHY(PHY_REG_BMCR);
    
    //shouldn't need the EMAC now.
    Peripheral_PowerDown(LPC1768_PCONP_PCENET);
    
    //and turn off the PHY OSC
     LPC_GPIO1->FIODIR |= 0x8000000;
     LPC_GPIO1->FIOCLR = 0x8000000;
}

static void write_PHY (unsigned int PhyReg, unsigned short Value) {
    /* Write a data 'Value' to PHY register 'PhyReg'. */
    unsigned int tout;
    /* Hardware MII Management for LPC176x devices. */
    LPC_EMAC->MADR = DP83848C_DEF_ADR | PhyReg;
    LPC_EMAC->MWTD = Value;
 
    /* Wait utill operation completed */
    for (tout = 0; tout < MII_WR_TOUT; tout++) {
        if ((LPC_EMAC->MIND & MIND_BUSY) == 0) {
            break;
        }
    }
}
 
static unsigned short read_PHY (unsigned int PhyReg) {
   /* Read a PHY register 'PhyReg'. */
   unsigned int tout, val;
 
   LPC_EMAC->MADR = DP83848C_DEF_ADR | PhyReg;
   LPC_EMAC->MCMD = MCMD_READ;
 
   /* Wait until operation completed */
   for (tout = 0; tout < MII_RD_TOUT; tout++) {
      if ((LPC_EMAC->MIND & MIND_BUSY) == 0) {
         break;
      }
   }
   LPC_EMAC->MCMD = 0;
   val = LPC_EMAC->MRDD;
   
   return (val);
}

void EMAC_Init()
{
    unsigned int tout,regv;
    /* Power Up the EMAC controller. */
    Peripheral_PowerUp(LPC1768_PCONP_PCENET);
  
    LPC_PINCON->PINSEL2 = 0x50150105;
    LPC_PINCON->PINSEL3 &= ~0x0000000F;
    LPC_PINCON->PINSEL3 |= 0x00000005;
 
    /* Reset all EMAC internal modules. */
    LPC_EMAC->MAC1 = MAC1_RES_TX | MAC1_RES_MCS_TX | MAC1_RES_RX | MAC1_RES_MCS_RX |
             MAC1_SIM_RES | MAC1_SOFT_RES;
    LPC_EMAC->Command = CR_REG_RES | CR_TX_RES | CR_RX_RES;
 
    /* A short delay after reset. */
    for (tout = 100; tout; tout--);
 
    /* Initialize MAC control registers. */
    LPC_EMAC->MAC1 = MAC1_PASS_ALL;
    LPC_EMAC->MAC2 = MAC2_CRC_EN | MAC2_PAD_EN;
    LPC_EMAC->MAXF = ETH_MAX_FLEN;
    LPC_EMAC->CLRT = CLRT_DEF;
    LPC_EMAC->IPGR = IPGR_DEF;
 
    /* Enable Reduced MII interface. */
    LPC_EMAC->Command = CR_RMII | CR_PASS_RUNT_FRM;
 
    /* Reset Reduced MII Logic. */
    LPC_EMAC->SUPP = SUPP_RES_RMII;
    for (tout = 100; tout; tout--);
    LPC_EMAC->SUPP = 0;
 
    /* Put the DP83848C in reset mode */
    write_PHY (PHY_REG_BMCR, 0x8000);
 
    /* Wait for hardware reset to end. */
    for (tout = 0; tout < 0x100000; tout++) {
        regv = read_PHY (PHY_REG_BMCR);
        if (!(regv & 0x8000)) {
            /* Reset complete */
            break;
        }
    }
}
  
/**
@brief Functions used to display characters and shapes.
@brief Acknowledgements to Dr.Craig A. Evans's code.
*/
N5110::N5110(PinName pwrPin, PinName scePin, PinName rstPin, PinName dcPin, PinName mosiPin, PinName sclkPin, PinName ledPin)
{

    spi = new SPI(mosiPin,NC,sclkPin); // create new SPI instance and initialise
    initSPI();

    // set up pins as required
    led = new PwmOut(ledPin);
    pwr = new DigitalOut(pwrPin);
    sce = new DigitalOut(scePin);
    rst = new DigitalOut(rstPin);
    dc = new DigitalOut(dcPin);

}

// initialise function - powers up and sends the initialisation commands
void N5110::init()
{
    turnOn();     // power up
    wait_ms(10);  // small delay seems to prevent spurious pixels during mbed reset
    reset();      // reset LCD - must be done within 100 ms

    // function set - extended
    sendCommand(0x20 | CMD_FS_ACTIVE_MODE | CMD_FS_HORIZONTAL_MODE | CMD_FS_EXTENDED_MODE);
    // Don't completely understand these parameters - they seem to work as they are
    // Consult the datasheet if you need to change them
    sendCommand(CMD_VOP_7V38);    // operating voltage - these values are from Chris Yan's Library
    sendCommand(CMD_TC_TEMP_2);   // temperature control
    sendCommand(CMD_BI_MUX_48);   // bias

    // function set - basic
    sendCommand(0x20 | CMD_FS_ACTIVE_MODE | CMD_FS_HORIZONTAL_MODE | CMD_FS_BASIC_MODE);
    normalMode();  // normal video mode by default
    sendCommand(CMD_DC_NORMAL_MODE);  // black on white

    // RAM is undefined at power-up so clear
    clearRAM();

}

// sets normal video mode (black on white)
void N5110::normalMode()
{
    sendCommand(CMD_DC_NORMAL_MODE);

}

// sets normal video mode (white on black)
void N5110::inverseMode()
{
    sendCommand(CMD_DC_INVERT_VIDEO);
}

// function to power up the LCD and backlight
void N5110::turnOn()
{
    // set brightness of LED - 0.0 to 1.0 - default is 50%
    setBrightness(0.5);
    pwr->write(1);  // apply power
}

// function to power down LCD
void N5110::turnOff()
{
    setBrightness(0.0);  // turn backlight off
    clearRAM();   // clear RAM to ensure specified current consumption
    // send command to ensure we are in basic mode
    sendCommand(0x20 | CMD_FS_ACTIVE_MODE | CMD_FS_HORIZONTAL_MODE | CMD_FS_BASIC_MODE);
    // clear the display
    sendCommand(CMD_DC_CLEAR_DISPLAY);
    // enter the extended mode and power down
    sendCommand(0x20 | CMD_FS_POWER_DOWN_MODE | CMD_FS_HORIZONTAL_MODE | CMD_FS_EXTENDED_MODE);
    // small delay and then turn off the power pin
    wait_ms(10);
    pwr->write(0);

}

// function to change LED backlight brightness
void N5110::setBrightness(float brightness)
{
    // check whether brightness is within range
    if (brightness < 0.0)
        brightness = 0.0;
    if (brightness > 1.0)
        brightness = 1.0;
    // set PWM duty cycle
    led->write(brightness);
}

// pulse the active low reset line
void N5110::reset()
{
    rst->write(0);  // reset the LCD
    rst->write(1);
}

// function to initialise SPI peripheral
void N5110::initSPI()
{
    spi->format(8,1);    // 8 bits, Mode 1 - polarity 0, phase 1 - base value of clock is 0, data captured on falling edge/propagated on rising edge
    spi->frequency(4000000);  // maximum of screen is 4 MHz
}

// send a command to the display
void N5110::sendCommand(unsigned char command)
{
    dc->write(0);  // set DC low for command
    sce->write(0); // set CE low to begin frame
    spi->write(command);  // send command
    dc->write(1);  // turn back to data by default
    sce->write(1); // set CE high to end frame (expected for transmission of single byte)

}

// this function writes 0 to the 504 bytes to clear the RAM
void N5110::clearRAM()
{
    int i;
    sce->write(0);  //set CE low to begin frame
    for(i = 0; i < WIDTH * HEIGHT; i++) { // 48 x 84 bits = 504 bytes
        spi->write(0x00);  // send 0's
    }
    sce->write(1); // set CE high to end frame

}

// function to set the XY address in RAM for subsequenct data write
void N5110::setXYAddress(int x, int y)
{
    if (x>=0 && x<WIDTH && y>=0 && y<HEIGHT) {  // check within range
        sendCommand(0x80 | x);  // send addresses to display with relevant mask
        sendCommand(0x40 | y);
    }
}

// These functions are used to set, clear and get the value of pixels in the display
// Pixels are addressed in the range of 0 to 47 (y) and 0 to 83 (x).  The refresh()
// function must be called after set and clear in order to update the display
void N5110::setPixel(int x, int y)
{
    if (x>=0 && x<WIDTH && y>=0 && y<HEIGHT) {  // check within range
        // calculate bank and shift 1 to required position in the data byte
        buffer[x][y/8] |= (1 << y%8);
    }
}

void N5110::clearPixel(int x, int y)
{
    if (x>=0 && x<WIDTH && y>=0 && y<HEIGHT) {  // check within range
        // calculate bank and shift 1 to required position (using bit clear)
        buffer[x][y/8] &= ~(1 << y%8);
    }
}

// function to refresh the display
void N5110::refresh()
{
    int i,j;

    setXYAddress(0,0);  // important to set address back to 0,0 before refreshing display
    // address auto increments after printing string, so buffer[0][0] will not coincide
    // with top-left pixel after priting string

    sce->write(0);  //set CE low to begin frame

    for(j = 0; j < BANKS; j++) {  // be careful to use correct order (j,i) for horizontal addressing
        for(i = 0; i < WIDTH; i++) {
            spi->write(buffer[i][j]);  // send buffer
        }
    }
    sce->write(1); // set CE high to end frame

}

// function to print string at specified position
void N5110::printString(const char * str,int x,int y)
{
    if (y>=0 && y<BANKS) {  // check if printing in range of y banks

        int n = 0 ; // counter for number of characters in string
        // loop through string and print character
        while(*str) {

            // writes the character bitmap data to the buffer, so that
            // text and pixels can be displayed at the same time
            for (int i = 0; i < 5 ; i++ ) {
                int pixel_x = x+i+n*6;
                if (pixel_x > WIDTH-1) // ensure pixel isn't outside the buffer size (0 - 83)
                    break;
                buffer[pixel_x][y] = font5x7[(*str - 32)*5 + i];
            }

            str++;  // go to next character in string

            n++;    // increment index

        }

        refresh();  // this sends the buffer to the display and sets address (cursor) back to 0,0
    }
}

// function to clear the screen
void N5110::clear()
{
    clearBuffer();  // clear the buffer then call the refresh function
    refresh();
}

// function to clear the buffer
void N5110::clearBuffer()
{
    int i,j;
    for (i=0; i<WIDTH; i++) {  // loop through the banks and set the buffer to 0
        for (j=0; j<BANKS; j++) {
            buffer[i][j]=0;
        }
    }
}

// function to draw circle
void N5110:: drawCircle(int x0,int y0,int radius,int fill)
{
    // from http://en.wikipedia.org/wiki/Midpoint_circle_algorithm
    int x = radius;
    int y = 0;
    int radiusError = 1-x;

    while(x >= y) {

        // if transparent, just draw outline
        if (fill == 0) {
            setPixel( x + x0,  y + y0);
            setPixel(-x + x0,  y + y0);
            setPixel( y + x0,  x + y0);
            setPixel(-y + x0,  x + y0);
            setPixel(-y + x0, -x + y0);
            setPixel( y + x0, -x + y0);
            setPixel( x + x0, -y + y0);
            setPixel(-x + x0, -y + y0);
        } else {  // drawing filled circle, so draw lines between points at same y value

            int type = (fill==1) ? 1:0;  // black or white fill

            drawLine(x+x0,y+y0,-x+x0,y+y0,type);
            drawLine(y+x0,x+y0,-y+x0,x+y0,type);
            drawLine(y+x0,-x+y0,-y+x0,-x+y0,type);
            drawLine(x+x0,-y+y0,-x+x0,-y+y0,type);
        }


        y++;
        if (radiusError<0) {
            radiusError += 2 * y + 1;
        } else {
            x--;
            radiusError += 2 * (y - x) + 1;
        }
    }

}

void N5110::drawLine(int x0,int y0,int x1,int y1,int type)
{
    int y_range = y1-y0;  // calc range of y and x
    int x_range = x1-x0;
    int start,stop,step;

    // if dotted line, set step to 2, else step is 1
    step = (type==2) ? 2:1;

    // make sure we loop over the largest range to get the most pixels on the display
    // for instance, if drawing a vertical line (x_range = 0), we need to loop down the y pixels
    // or else we'll only end up with 1 pixel in the x column
    if ( abs(x_range) > abs(y_range) ) {

        // ensure we loop from smallest to largest or else for-loop won't run as expected
        start = x1>x0 ? x0:x1;
        stop =  x1>x0 ? x1:x0;

        // loop between x pixels
        for (int x = start; x<= stop ; x+=step) {
            // do linear interpolation
            int y = y0 + (y1-y0)*(x-x0)/(x1-x0);

            if (type == 0)   // if 'white' line, turn off pixel
                clearPixel(x,y);
            else
                setPixel(x,y);  // else if 'black' or 'dotted' turn on pixel
        }
    } else {

        // ensure we loop from smallest to largest or else for-loop won't run as expected
        start = y1>y0 ? y0:y1;
        stop =  y1>y0 ? y1:y0;

        for (int y = start; y<= stop ; y+=step) {
            // do linear interpolation
            int x = x0 + (x1-x0)*(y-y0)/(y1-y0);

            if (type == 0)   // if 'white' line, turn off pixel
                clearPixel(x,y);
            else
                setPixel(x,y);  // else if 'black' or 'dotted' turn on pixel

        }
    }

}

MMA8452:: MMA8452(PinName sdaPin, PinName sclPin)
{
    i2c = new I2C(sdaPin,sclPin); // create new I2C instance and initialise
    i2c->frequency(400000);       // I2C Fast Mode - 400kHz
    leds = new BusOut(LED4,LED3,LED2,LED1);  // for debug
}

void MMA8452::init()
{

    i2c->frequency(400000); // set Fast Mode I2C frequency (5.10 datasheet)

    char data = readByteFromRegister(WHO_AM_I);  // p18 datasheet
    if (data != 0x2A) { // if correct ID not found, hand and flash error message
        error();
    }

    // put into STANDBY while configuring
    data = readByteFromRegister(CTRL_REG1); // get current value of register
    data &= ~(1<<0); // clear bit 0 (p37 datasheet)
    sendByteToRegister(data,CTRL_REG1);

    // Set output data rate, default is 800 Hz, will set to 100 Hz (clear b5, set b4/b3 - p37 datasheet)
    data = readByteFromRegister(CTRL_REG1);
    data &= ~(1<<5);
    data |=  (1<<4);
    data |=  (1<<3);
    sendByteToRegister(data,CTRL_REG1);

    //// Can also change default 2g range to 4g or 8g (p22 datasheet)
    data = readByteFromRegister(XYZ_DATA_CFG);
    data |=  (1<<0); // set bit 0 - 4g range
    sendByteToRegister(data,XYZ_DATA_CFG);

    // set ACTIVE
    data = readByteFromRegister(CTRL_REG1);
    data |= (1<<0);   // set bit 0 in CTRL_REG1
    sendByteToRegister(data,CTRL_REG1);

}

// read acceleration data from device
Acceleration MMA8452::readValues()
{
    // acceleration data stored in 6 registers (0x01 to 0x06)
    // device automatically increments register, so can read 6 bytes starting from OUT_X_MSB
    char data[6];
    readBytesFromRegister(OUT_X_MSB,6,data);

    char x_MSB = data[0];  // extract MSB and LSBs for x,y,z values
    char x_LSB = data[1];
    char y_MSB = data[2];
    char y_LSB = data[3];
    char z_MSB = data[4];
    char z_LSB = data[5];

    // [0:7] of MSB are 8 MSB of 12-bit value , [7:4] of LSB are 4 LSB's of 12-bit value
    // need to type-cast as numbers are in signed (2's complement) form (p20 datasheet)
    int x = (int16_t) (x_MSB << 8) | x_LSB;  // combine bytes
    x >>= 4;  // are left-aligned, so shift 4 places right to right-align
    int y = (int16_t) (y_MSB << 8) | y_LSB;
    y >>= 4;
    int z = (int16_t) (z_MSB << 8) | z_LSB;
    z >>= 4;

    // sensitivity is 1024 counts/g in 2g mode (pg 9 datasheet)
    //  "   "          512      "      4g     "
    //  "   "          256      "      8g     "
    Acceleration acc;
    
    acc.x = x/512.0;
    acc.y = y/512.0;
    acc.z = z/512.0;
    
    return acc;
}

// reads a byte from a specific register
char MMA8452::readByteFromRegister(char reg)
{
    int nack = i2c->write(MMA8452_W_ADDRESS,&reg,1,true);  // send the register address to the slave
    // true as need to send repeated start condition (5.10.1 datasheet)
    // http://www.i2c-bus.org/repeated-start-condition/
    if (nack)
        error();  // if we don't receive acknowledgement, flash error message

    char rx;
    nack = i2c->read(MMA8452_R_ADDRESS,&rx,1);  // read a byte from the register and store in buffer
    if (nack)
        error();  // if we don't receive acknowledgement, flash error message

    return rx;
}

// reads a series of bytes, starting from a specific register
void MMA8452::readBytesFromRegister(char reg,int numberOfBytes,char bytes[])
{

    int nack = i2c->write(MMA8452_W_ADDRESS,&reg,1,true);  // send the slave write address and the configuration register address
    // true as need to send repeated start condition (5.10.1 datasheet)
    // http://www.i2c-bus.org/repeated-start-condition/

    if (nack)
        error();  // if we don't receive acknowledgement, flash error message

    nack = i2c->read(MMA8452_R_ADDRESS,bytes,numberOfBytes);  // read bytes
    if (nack)
        error();  // if we don't receive acknowledgement, flash error message

}

// sends a byte to a specific register
void MMA8452::sendByteToRegister(char byte,char reg)
{
    char data[2];
    data[0] = reg;
    data[1] = byte;
    // send the register address, followed by the data
    int nack = i2c->write(MMA8452_W_ADDRESS,data,2);
    if (nack)
        error();  // if we don't receive acknowledgement, flash error message

}

void MMA8452::error()
{
    while(1) {
        leds->write(15);
        wait(0.1);
        leds->write(0);
        wait(0.1);
    }
}