src/temperature.c


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#include <avr/io.h>
#include <util/delay.h>

#include "temperature.h"

void temperature_init(void) {
  THERMO_DDR |= (1 << THERMO_CS) | (1 << THERMO_SCK);
  THERMO_DDR &= ~(1 << THERMO_MISO);
  THERMO_PORT |= (1 << THERMO_CS);
}

uint8_t spi_read8(void) {
  int i;
  uint8_t data = 0;

  for (i = 7; i >= 0; i--) {
    THERMO_PORT &= ~(1 << THERMO_SCK);
    _delay_us(SPI_DELAY_US);
    if (PINA & (1 << THERMO_MISO))
      data |= (1 << i);

    THERMO_PORT |= (1 << THERMO_SCK);
    _delay_us(SPI_DELAY_US);
  }

  return data;
}

uint16_t spi_read16(void) {
  uint16_t data;
  _delay_us(SPI_DELAY_US);
  data = spi_read8();
  data <<= 8;
  data |= spi_read8();
  return data;
}

float temperature_read(void) {
  THERMO_PORT &= ~(1 << THERMO_CS);
  uint16_t out = spi_read16();
  THERMO_PORT |= (1 << THERMO_CS);

  // thermocouple open (invalid read) D2 bit
  if (out & 0b100)
    return 0.0;

  out >>= 3; // Skip D0,D1,D2

  float temperature = out * THERMO_RESOLUTION;
  if (temperature > 100)
    temperature *= 1.05;
  return temperature;
}