// cap_meter.c

// Code to implement capacitance meter with Mega128.
// Implemented as integrating quantizer.

//compute a multiplicitive factor to make code cleaner. This is
//simply a cranking of the equation for current through a cap
//given the dv, Ic, and bandgap reference voltage.
#define DtoC_FACTOR 0.2340    //5V wall wart supply for accuracy

#include <avr/io.h>
#include <avr/interrupt.h>
#include <util/delay.h>
#include "lcd.h"
#include <string.h>

//global variable with LCD text, so ISR can change it
char lcd_message[14] = {"xxxx.x nF cap"};

/*****************************************************************************/
//SPI initalization for LCD display
void spi_init(void){}
/*****************************************************************************/

/*****************************************************************************/
//Comparator init
//Use bandgap reference (1.23V), Input capture trigger for TCNT1 enabled 
void acomp_init(void){}
/*****************************************************************************/

/*****************************************************************************/
//TCNT3_init
//Run in normal mode. Used to set the refresh rate for the LCD display.
//Refresh rate shold be about 4mS. Does not generate interrupts. Poll for
//interrupt flag.
void tcnt3_init(void){}
/*****************************************************************************/

/*****************************************************************************/
//TCNT1_init
//Use in normal mode. Suggest no pre-scaler. Start up initially with counter off.
//Must enable TCNT1 input capture and overflow interrupts.
//
void tcnt1_init(void){}
/*****************************************************************************/

/*****************************************************************************/
//Input capture register ISR
//When input capture register interrupt happens: 
//  - read counter 1 value
//  - disable counter
//  - convert to cap value
//  - fill in the LCD message string only 
//
ISR(TIMER1_CAPT_vect){}
/*****************************************************************************/

/*****************************************************************************/
//                              timer1 overflow ISR
//If TCNT1 overflows, before the analog comparator triggers, disable counter
// and display "---.-" to LCD
//
ISR(TIMER1_OVF_vect){}
/*****************************************************************************/

/*****************************************************************************/
int main(){
    //setup PORTB.0 LED for blinking
    //setup PORTF.3 to clock LCD    
    //set PE2,3 appropriately
    //initalize SPI
    //initialize counter/timer one
    //initialize counter/timer three
    //initialize analog comparator
    //wait enough time for bandgap reference to startup 
    //initialize the LCD
    //enable interrupts

    while(1){
        if (TCNT3 overflowed){   
            //clear overflow bit for next measurement
            //toggle B0 to see that the meter is running
            //ensure that TCNT1 starts at zero to time the charge interval
            //make PE2 an output to discharge cap
            //delay enough to discharge the cap 
            //start TC1 counter, no prescaling (62.5nS/tick)
            //change PE2 back to high-Z (input) to allow charging cap
            //write string to LCD; message is created in the ISR
            //put the cursor back to home
        }//if
    }//while
}//main