Three-Axis Digital Compass IC HMC5883L

Code C - [expand]
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/*
    5-18-10
    Copyright Spark Fun Electronics© 2010
    Nathan Seidle
    
    Example I2C to control the HMC5843 3-axis magnetometer
    
    Based on Aaron Weiss' code.
    
    Designed to run on an Arduino using the standard serial bootloader.
    This is not written in Arduino, this is a C example.
    
    Things to know: 
    Unlike other I2C devices, in the HMC5843 you can keep reading registers and 
    the adress pointer will continue to increment.
    
    The only register you have to write to, to get the HMC5843 to start outputting data
    is 0x02, the 'Mode' register. You have to clear bit 1 (MD1) to go into continous coversion mode.
    
    Don't forget to enable or add pullups to SDA/SCL. This firmware uses the internal
    pullups. Should work fine without them.
    
    SCL is Analog pin 5 (aka PC5)
    SDA is Analog pin 4 (aka PC4)
*/
 
#include <stdio.h>
#include <avr/io.h>
#include "i2c.h" //Needed for I2C sensors
 
#define HMC5843_W   0x3C
#define HMC5843_R   0x3D
 
//#define FALSE 0
//#define TRUE  -1
 
#define FOSC 16000000 //16MHz external osc
 
#define SERIAL_BAUD 9600
#define SERIAL_MYUBRR (((((FOSC * 10) / (16L * SERIAL_BAUD)) + 5) / 10) - 1)
 
//Function definitions
//=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
void ioinit(void);
void delay_ms(uint16_t x);
void delay_us(uint16_t x);
int uart_putchar(char c, FILE *stream);
 
int16_t read_hmc5843(char reg_adr);
void init_hmc5843(void);
//=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
 
//Global variables
//=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
static FILE mystdout = FDEV_SETUP_STREAM(uart_putchar, NULL, _FDEV_SETUP_WRITE);
//=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
 
int main (void)
{
    int16_t x, y, z;
 
    ioinit(); //Boot up defaults
 
    i2cInit(); //Get the I2C bus ready
 
    printf("HMC5843 Example\n");
 
    init_hmc5843(); //Write to 0x02 Mode register - clear MD1 bit
    
    while(1)
    {
        x = read_hmc5843(0x03);
        y = read_hmc5843(0x05);
        z = read_hmc5843(0x07);
 
        printf("x=%04d, y=%04d, z=%04d\n", x, y, z);
 
        if ((UCSR0A & _BV(RXC0))) //Check for incoming RX characters
            if(UDR0 == 'x') break;
            
        delay_ms(100); //10Hz readings by default
    }
    
    printf("You've gone too far!");
    while(1);
 
    return(0);
}
 
void ioinit(void)
{
    //1 = output, 0 = input 
    DDRB = 0b11111111;
    DDRC = 0b11111111;
    DDRD = 0b11111111;
 
    PORTC = 0b00110000; //pullups on the I2C bus
    
    //Setup USART baud rate
    UBRR0H = SERIAL_MYUBRR >> 8;
    UBRR0L = SERIAL_MYUBRR;
    UCSR0B = (1<<RXEN0)|(1<<TXEN0); //No receive interrupt
    UCSR0A ^= (1<<U2X0); //This clears the double speed UART transmission that may be set by the Arduino bootloader
 
    stdout = &mystdout; //Required for printf init
 
    //Init Timer0 for delay_us
    TCCR0B = (1<<CS01); //Set Prescaler to clk/8 : 1click = 0.5us(assume we are running at external 16MHz). CS01=1 
}
 
int16_t read_hmc5843(char reg_adr)
{       
    char lsb, msb;
 
    i2cSendStart();
    i2cWaitForComplete();
    
    i2cSendByte(HMC5843_W); // write to this I2C address, R/*W cleared
    i2cWaitForComplete();
    
    i2cSendByte(reg_adr);   //Read from a given address
    i2cWaitForComplete();
    
    i2cSendStart();
    
    i2cSendByte(HMC5843_R); // read from this I2C address, R/*W Set
    i2cWaitForComplete();
    
    i2cReceiveByte(TRUE);
    i2cWaitForComplete();
    msb = i2cGetReceivedByte(); //Read the LSB data
    i2cWaitForComplete();
 
    i2cReceiveByte(FALSE);
    i2cWaitForComplete();
    lsb = i2cGetReceivedByte(); //Read the MSB data
    i2cWaitForComplete();
    
    i2cSendStop();
    
    return( (msb<<8) | lsb);
}
 
//Setup HMC5843 for constant measurement mode
void init_hmc5843(void)
{
    i2cSendStart();
    i2cWaitForComplete();
 
    i2cSendByte(HMC5843_W); //write to the HMC5843
    i2cWaitForComplete();
 
    i2cSendByte(0x02); //Write to Mode register
    i2cWaitForComplete();
 
    i2cSendByte(0x00); //Clear bit 1, the MD1 bit
    i2cWaitForComplete();
 
    i2cSendStop();
}
 
//General short delays
void delay_ms(uint16_t x)
{
    for (; x > 0 ; x--)
    {
        delay_us(250);
        delay_us(250);
        delay_us(250);
        delay_us(250);
    }
}
 
//General short delays
void delay_us(uint16_t x)
{
    x *= 2; //Runs at 16MHz instead of normal 8MHz
 
    while(x > 256)
    {
        TIFR0 = (1<<TOV0); //Clear any interrupt flags on Timer2
        TCNT0 = 0; //256 - 125 = 131 : Preload timer 2 for x clicks. Should be 1us per click
        while( (TIFR0 & (1<<TOV0)) == 0);
        
        x -= 256;
    }
 
    TIFR0 = (1<<TOV0); //Clear any interrupt flags on Timer2
    TCNT0 = 256 - x; //256 - 125 = 131 : Preload timer 2 for x clicks. Should be 1us per click
    while( (TIFR0 & (1<<TOV0)) == 0);
}
 
int uart_putchar(char c, FILE *stream)
{
    if (c == '\n') uart_putchar('\r', stream);
  
    loop_until_bit_is_set(UCSR0A, UDRE0);
    UDR0 = c;
 
    return 0;
}