// a2d.c - A2D functions
//
// Version 14.3
// ADC prescaler changed to 64, to give 125kHz AD clock freq.
// With continious sampling, this gives 4,580 samples per second per channel.

#include <avr/io.h>
#include "a2d.h"

// Static variables holding the latest values from the ADC

static short ADValue[8];

// ----------------------------------------------------------------------------------------------------------------------------------------------------------------
// Initialize Analogue to Digital converters.
// Use single ended conversion - one channel at a time, 
// Setup to sample channels only when triggered. (not free running)
// For accurate 10 bit conversion, AD clock must be between 50kHz and 200kHz

void A2D_Init(void)
{
  uint8_t n;
  for (n=0;n<8;n++) ADValue[n] = 400;
		
  ADCSRA = (1<<ADPS1) | (1<<ADPS2);		// Prescale 64 .. @8Mhz ADC clock = 125kHz
  
  ADMUX = (1<<REFS0) | (0x03);	/* start with ADC3 */

  ADCSRA |= (1<<ADEN);	// Enable the ADC
  ADCSRA |= (1<<ADSC);	// Start conversions
}

// ---------------------------------------------------------------------------------------------
// poll a2d conversion complete bit - read ADC, start next conversion.
// This avoids waiting or having to turn off interupts to read/write values.
// Sample 8 channels in sequence [0..7] then start over at 0.
// Filter noise using low pass averaging.
// This routine will be called 168,000 times per second. (at 8Mhz)
// Conversions take a couple of cycles to complete.
// It works out to over 9,000 samples per second.

void A2D_poll_adc(void)
{
  uint8_t chanNum;
  
  if (bit_is_clear(ADCSRA, ADSC)){	// if clear, conversion is done.
    
      chanNum = (ADMUX & 0x07);	// Check which channel was just measured
      
      // ADValue[chanNum++] = ADC;	// Save measured value - no filtering
      
      ADValue[chanNum] = ((ADValue[chanNum] * 3) + ADC) / 4;	// Average measured value
      chanNum++;
      if(chanNum > 0x07) chanNum = 0x03; /* only use high-order pins (pinc0-pinc2 are digital inputs) */
      
      //      ADMUX = (1<<REFS0) | (chanNum & 0x01);	// Use AVCC voltage ref, channel num 0..1
      ADMUX = (1<<REFS0) | (chanNum & 0x07);	// Use AVCC voltage ref, channel num 0..1
      //      putU8(chanNum);
      //putstr("\r\n");
      ADCSRA |= _BV(ADSC); // Start next conversion
    }
}

// --------------------------------------------------------------------------------
// Return most recent value read from A2D converter for requested channel.
// This avoids waiting or having to turn off interupts to read/write values.

short A2D_read_channel(uint8_t chanNum)
{
  if (chanNum < 8)
    return ADValue[chanNum];
  else
    return 0;
}

// ------------------------------------------------------------------------------------
// End of File