#!/usr/bin/python
import smbus
import time

bus = smbus.SMBus(1) # or bus = smbus.SMBus(1) if you have a revision 2 board 
address = 0x77

def read_byte(adr):
    return bus.read_byte_data(address, adr)

def read_word(adr):
    high = bus.read_byte_data(address, adr)
    low = bus.read_byte_data(address, adr+1)
    val = (high << 8) + low
    return val

def read_word_2c(adr):
    val = read_word(adr)
    if (val >= 0x8000):
        return -((0xffff - val) + 1)
    else:
        return val

def write_byte(adr, value):
    bus.write_byte_data(address, adr, value)

def twos_compliment(val):
    if (val >= 0x8000):
        return -((0xffff - val) + 1)
    else:
        return val

def get_word(array, index, twos):
    val = (array[index] << 8) + array[index+1]
    if twos:
        return twos_compliment(val)
    else:
        return val

def calculate():
    # This code is a direct translation from the datasheet
    # and should be optimised for real world use
    
    #Calculate temperature
    x1 = ((temp_raw - ac6) * ac5) / 32768
    x2 = (mc * 2048) / (x1 + md)
    b5 = x1 + x2
    t = (b5 + 8) / 16
    
    # Now calculate the pressure
    b6 = b5 - 4000 
    x1 = (b2 * (b6 * b6 >> 12)) >> 11
    x2 = ac2 * b6 >> 11
    x3 = x1 + x2
    b3 = (((ac1 * 4 + x3) << oss) + 2) >> 2 
    
    x1 = (ac3 * b6) >> 13 
    x2 = (b1 * (b6 * b6 >> 12)) >> 16 
    x3 = ((x1 + x2) + 2) >> 2 
    b4 = ac4 * (x3 + 32768) >> 15 
    b7 = (pressure_raw - b3) * (50000 >> oss)
    if (b7 < 0x80000000):
        p = (b7 * 2) /b4
    else:
        p = (b7 / b4) *2
    x1 = (p >> 8) * (p >> 8)
    x1 = (x1 * 3038) >> 16
    x2 = (-7357 * p) >> 16
    p = p + ((x1 + x2 + 3791) >> 4)
    return(t,p)

calibration = bus.read_i2c_block_data(address, 0xAA, 22)

oss = 3              # Ultra high resolution
temp_wait_period = 0.004
pressure_wait_period = 0.0255 # Conversion time

# The sensor has a block of factory set calibration values we need to read
# these are then used in a length calculation to get the temperature and pressure
ac1 = get_word(calibration, 0, True)
ac2 = get_word(calibration, 2, True)
ac3 = get_word(calibration, 4, True)
ac4 = get_word(calibration, 6, False)
ac5 = get_word(calibration, 8, False)
ac6 = get_word(calibration, 10, False)
b1 =  get_word(calibration, 12, True)
b2 =  get_word(calibration, 14, True)
mb =  get_word(calibration, 16, True)
mc =  get_word(calibration, 18, True)
md =  get_word(calibration, 20, True)


while True:
    # Read raw temperature
    write_byte(0xF4, 0x2E)          # Tell the sensor to take a temperature reading
    time.sleep(temp_wait_period)    # Wait for the conversion to take place
    temp_raw = read_word_2c(0xF6)

    write_byte(0xF4, 0x34 + (oss << 6)) # Tell the sensor to take a pressure reading
    time.sleep(pressure_wait_period)    # Wait for the conversion to take place
    pressure_raw = ((read_byte(0xF6) << 16) \
                     + (read_byte(0xF7) << 8) \
                     + (read_byte(0xF8)) ) >> (8-oss)


    temperature, pressure = calculate()
    print  temperature / 10., pressure / 100.
    time.sleep(1)