task2.c

ATMEL XMEGA ADC Compare Function program.

/*
 *                                    -= Task 2 =-
 *
 *  In addition to normal single ended conversions the ADC also has a compare function. 
 *  When this is used, the ADC can be set up to do continues conversions, but it will 
 *  not signal a result (i.e. set the channel抯 interrupt flag) before the result is 
 *  above or below a selectable threshold value. This feature is very useful for 
 *  applications where you only wish to check that the input signal is not higher or 
 *  lower than a specific voltage. Without the compare function, it would be  natural 
 *  to check the result in software for every conversion. With the compare function in 
 *  the XMEGA DAC, the application will signal an interrupt or event when the threshold 
 *  is reached. This reduces the CPU load, and keeps the resource use to a minimum. 
 */

#include <avr/io.h> 
#include <avr/interrupt.h>
#include "../adc_driver.h"

#define LEDPORT PORTD

volatile uint8_t offset;
volatile uint16_t ADC_result;

ISR(ADCA_CH0_vect)
{   
    // Getting the 8MSB of the result 
    ADC_result = ADCA.CH0.RES;
    // Ignore negative results
    if(ADC_result > 0x07FF)
    {
        ADC_result = 0;
    }
    ADC_result = (ADC_result >> 4);
}

int main( void )
{
  	/* Move stored calibration values to ADC A. */
	ADC_CalibrationValues_Set(&ADCA);

	/* Get offset value for ADC A. */
 	offset = ADC_Offset_Get(&ADCA);

    // Set as output, the 8 MSB of the ADC result is output here
    LEDPORT.DIR = 0xFF; 
    // Turn off the LEDs as Default
    LEDPORT.OUT = 0xFF; 

	// Set up ADC A to have signed conversion mode and a adjusted 12 bit resolution
  	ADC_ConvMode_and_Resolution_Config(&ADCA, true, ADC_RESOLUTION_12BIT_gc);

	// Sample rate is CPUFREQ/8. Allow time for storing data
	ADC_Prescaler_Config(&ADCA, ADC_PRESCALER_DIV8_gc);

	// Set reference voltage on ADC A to be VCC-0.6 V
	ADC_Reference_Config(&ADCA, ADC_REFSEL_VCC_gc);

	// Setup channel 0, 1, 2 and 3 to have single ended input
	ADC_Ch_InputMode_and_Gain_Config(&ADCA.CH0,
	                                 ADC_CH_INPUTMODE_SINGLEENDED_gc,
	                                 ADC_CH_GAIN_1X_gc);
 
    // Set input to the channels in ADC A to be PIN 1
	ADC_Ch_InputMux_Config( &ADCA.CH0, 
                            ADC_CH_MUXPOS_PIN1_gc, 
                            0);   

    // The ADC Compare (CMP) register must be set with the threshold value when
    // compare mode is used. Add code that sets the CMP register to the half of 
    // the ADCA resolution
    ADCA.CMP = (0x800 / 2); 
    
    // Wait until common mode voltage is stable. Default clk is 2MHz and
	// therefore below the maximum frequency to use this function. 
	ADC_Wait_8MHz(&ADCA);

    // Setup Interrupt Mode Above Compare Value (ADCA.CMP)
    ADC_Ch_Interrupts_Config(   &ADCA.CH0, 
                                // INSERT CODE 
								ADC_CH_INTMODE_ABOVE_gc,
                                ADC_CH_INTLVL_MED_gc);

    // Enable the Medium Level interrupts needed in the PMIC 
    // ADD CODE HERE
	PMIC.CTRL |= PMIC_MEDLVLEN_bm; 
    // Enable free running mode
	ADC_FreeRunning_Enable(&ADCA);

    // Enable ADC A 
	ADC_Enable(&ADCA);

    // Enable Global interrupts
    sei();
  
    while(1)
    {
        // Invert the output since a pin high is LED off     
        LEDPORT.OUT = ~ADC_result; 
    }
}