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

Make AVR Examples/Chapter17_I2C/loggingThermometer/25LC256.c

@@ -0,0 +1,105 @@
+#include "25LC256.h"
+
+void initSPI(void) {
+  SPI_SS_DDR |= (1 << SPI_SS);                        /* set SS output */
+  SPI_SS_PORT |= (1 << SPI_SS);       /* start off not selected (high) */
+
+  SPI_MOSI_DDR |= (1 << SPI_MOSI);                   /* output on MOSI */
+  SPI_MISO_PORT |= (1 << SPI_MISO);                  /* pullup on MISO */
+  SPI_SCK_DDR |= (1 << SPI_SCK);                      /* output on SCK */
+
+  /* Don't have to set phase, polarity b/c
+     default works with 25LCxxx chips */
+  SPCR |= (1 << SPR1);                /* div 16, safer for breadboards */
+  SPCR |= (1 << MSTR);                                  /* clockmaster */
+  SPCR |= (1 << SPE);                                        /* enable */
+}
+
+void SPI_tradeByte(uint8_t byte) {
+  SPDR = byte;                       /* SPI starts sending immediately */
+  loop_until_bit_is_set(SPSR, SPIF);                /* wait until done */
+                                /* SPDR now contains the received byte */
+}
+
+void EEPROM_send16BitAddress(uint16_t address) {
+  SPI_tradeByte((uint8_t) (address >> 8));    /* most significant byte */
+  SPI_tradeByte((uint8_t) address);          /* least significant byte */
+}
+
+uint8_t EEPROM_readStatus(void) {
+  SLAVE_SELECT;
+  SPI_tradeByte(EEPROM_RDSR);
+  SPI_tradeByte(0);                            /* clock out eight bits */
+  SLAVE_DESELECT;
+  return (SPDR);                                  /* return the result */
+}
+
+void EEPROM_writeEnable(void) {
+  SLAVE_SELECT;
+  SPI_tradeByte(EEPROM_WREN);
+  SLAVE_DESELECT;
+}
+
+uint8_t EEPROM_readByte(uint16_t address) {
+  SLAVE_SELECT;
+  SPI_tradeByte(EEPROM_READ);
+  EEPROM_send16BitAddress(address);
+  SPI_tradeByte(0);
+  SLAVE_DESELECT;
+  return (SPDR);
+}
+
+uint16_t EEPROM_readWord(uint16_t address) {
+  uint16_t eepromWord;
+  SLAVE_SELECT;
+  SPI_tradeByte(EEPROM_READ);
+  EEPROM_send16BitAddress(address);
+  SPI_tradeByte(0);
+  eepromWord = SPDR;
+  eepromWord = (eepromWord << 8);                      /* most-sig bit */
+  SPI_tradeByte(0);
+  eepromWord += SPDR;                                 /* least-sig bit */
+  SLAVE_DESELECT;
+  return (eepromWord);
+}
+
+void EEPROM_writeByte(uint16_t address, uint8_t byte) {
+  EEPROM_writeEnable();
+  SLAVE_SELECT;
+  SPI_tradeByte(EEPROM_WRITE);
+  EEPROM_send16BitAddress(address);
+  SPI_tradeByte(byte);
+  SLAVE_DESELECT;
+  while (EEPROM_readStatus() & _BV(EEPROM_WRITE_IN_PROGRESS)) {;
+  }
+}
+
+void EEPROM_writeWord(uint16_t address, uint16_t word) {
+  EEPROM_writeEnable();
+  SLAVE_SELECT;
+  SPI_tradeByte(EEPROM_WRITE);
+  EEPROM_send16BitAddress(address);
+  SPI_tradeByte((uint8_t) (word >> 8));
+  SPI_tradeByte((uint8_t) word);
+  SLAVE_DESELECT;
+  while (EEPROM_readStatus() & _BV(EEPROM_WRITE_IN_PROGRESS)) {;
+  }
+}
+
+void EEPROM_clearAll(void) {
+  uint8_t i;
+  uint16_t pageAddress = 0;
+  while (pageAddress < EEPROM_BYTES_MAX) {
+    EEPROM_writeEnable();
+    SLAVE_SELECT;
+    SPI_tradeByte(EEPROM_WRITE);
+    EEPROM_send16BitAddress(pageAddress);
+    for (i = 0; i < EEPROM_BYTES_PER_PAGE; i++) {
+      SPI_tradeByte(0);
+    }
+    SLAVE_DESELECT;
+    pageAddress += EEPROM_BYTES_PER_PAGE;
+    while (EEPROM_readStatus() & _BV(EEPROM_WRITE_IN_PROGRESS)) {;
+    }
+  }
+}