Started following some tutorial on att85 usi. Downloaded example code from make avr book.

Make AVR Examples/Chapter18_Using-Flash-Program-Memory/talkingVoltmeter/talkingVoltmeter.h

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+/* Include file with DPCM data in it */
+#include "allDigits.h"
+#include <avr/pgmspace.h>
+
+// Now define sample-table names used in digits file 
+// From here on, no matter what you call the samples,
+//   you can refer to them as "ONE_TABLE", etc.  
+#define ONE_TABLE    DPCM_one_8000
+#define TWO_TABLE    DPCM_two_8000
+#define THREE_TABLE  DPCM_three_8000
+#define FOUR_TABLE   DPCM_four_8000
+#define FIVE_TABLE   DPCM_five_8000
+#define SIX_TABLE    DPCM_six_8000
+#define SEVEN_TABLE  DPCM_seven_8000
+#define EIGHT_TABLE  DPCM_eight_8000
+#define NINE_TABLE   DPCM_nine_8000
+#define ZERO_TABLE   DPCM_zero_8000
+#define POINT_TABLE  DPCM_point_8000
+#define VOLTS_TABLE  DPCM_volts_8000
+#define INTRO_TABLE  DPCM_talkingvoltmeter_8000
+
+#define SPEECH_DELAY   2000   /* milliseconds */
+
+/* --------------- Globals used by the ISR -------------- */
+volatile uint8_t* thisTableP; /* points at the current speech table */
+volatile uint16_t thisTableLength; /* length of current speech table */
+
+volatile uint16_t sampleNumber;         // sample index
+volatile int8_t   out, lastout;		// output values
+volatile uint8_t  differentials[4] = {0,0,0,0};	 
+const    int8_t   dpcmWeights[4]   = {-12, -3, 3, 12};
+
+
+/* These arrays let us choose a table (and its length) numerically */
+const uint16_t tableLengths[]  = {	/* all sample tables are 8-bit */
+  sizeof(ZERO_TABLE), sizeof(ONE_TABLE), sizeof(TWO_TABLE), 
+  sizeof(THREE_TABLE), sizeof(FOUR_TABLE), sizeof(FIVE_TABLE),
+  sizeof(SIX_TABLE), sizeof(SEVEN_TABLE), sizeof(EIGHT_TABLE), 
+  sizeof(NINE_TABLE), sizeof(POINT_TABLE), sizeof(VOLTS_TABLE), 
+  sizeof(INTRO_TABLE)
+};
+
+// Create an indexing table of all of the start addresses for
+// each spoken digit.  And then store this index in PROGMEM.
+const uint8_t* const tablePointers[] PROGMEM = { 
+  ZERO_TABLE, ONE_TABLE, TWO_TABLE, THREE_TABLE, FOUR_TABLE, 
+  FIVE_TABLE, SIX_TABLE, SEVEN_TABLE, EIGHT_TABLE, NINE_TABLE, 
+  POINT_TABLE, VOLTS_TABLE, INTRO_TABLE
+};
+
+void selectTable(uint8_t whichTable){
+  /* Set up global table pointer, lengths */
+  uint16_t pointerAddress;
+  thisTableLength = tableLengths[whichTable];
+  pointerAddress = (uint16_t) &tablePointers[whichTable];
+  thisTableP =  (uint8_t*) pgm_read_word(pointerAddress);
+}
+
+/* Extra defines for the non-numeric values */
+#define   POINT  10
+#define   VOLTS  11 
+#define   INTRO  12
+
+
+///-----------------   Init functions  -------------------///
+
+void initTimer0(void){
+  // Timer 0 Configured for free-running PWM Audio Output
+  TCCR0A |= (1<<WGM00) | (1<<WGM01); /* fast PWM mode */
+  TCCR0A |= (1<<COM0A0) | (1<<COM0A1); /* output on PD6/OC0A */
+  TCCR0B = (1<<CS00);		       /* fastest clock */
+  OCR0A = 128 ;			       /* initialize mid-value */
+  SPEAKER_DDR |= (1<<SPEAKER);	       /* output PD6 / OC0A */
+}
+
+void initTimer2(void){
+  // Timer 2 loads OCR0A, provides sampling frequency
+  TCCR2A = (1<<WGM21);	      /* CTC, count to OCR2A */
+  TIMSK2 = (1<<OCIE2A);	      /* turn on compare interrupt */
+  OCR2A = 128;	    /* controls sample playback frequency */
+  /* note: no clock source selected yet, so won't start up  */
+}
+
+void initADC(void){
+  // ADC for Voltmeter function
+  ADMUX  |= (0b00001111 & PC5);  /* set mux to ADC5 */
+  DIDR0 |= _BV(ADC5D);		 /* turn off digital circuitry on PC5 */
+  ADMUX  |= (1 << REFS0);        /* reference voltage is AVCC, 5V */
+  ADCSRA |= (1 << ADPS1) | (1 << ADPS2); /* ADC clock prescaler /64 */
+  ADCSRA |= (1 << ADEN);        /* enable ADC */
+}