#!/usr/bin/env python3

# vim: set ai et ts=4 sw=4:

# (c) Aleksander Alekseev 2018
# https://eax.me/

import sys
import time
import subprocess
from struct import pack, unpack

# oversampling setting
oss = 0         # 0..3

def read(addr):
    cmd = "i2cget -y 0 0x77 0x{:02X}".format(addr)
    res = subprocess.check_output(cmd, shell=True)
    res = res.decode('utf-8').strip()
    return int(res[2:4], base = 16)

def write(addr, val):
    cmd = "i2cset -y 0 0x77 0x{:02X} 0x{:02X}".format(addr, val)
    code = subprocess.call(cmd, shell=True)
    if code != 0:
        print("Command '{}' returned {}".format(cmd, code))
        sys.exit(1)

def signed_short(b1, b2):
    return unpack('h', pack('BB', b1, b2))[0]

def unsigned_short(b1, b2):
    return (b1 << 8) | b2
    # return unpack('H', pack('BB', b1, b2))[0]

# read calibration data

ac1 = signed_short(read(0xAA), read(0xAB))
ac2 = signed_short(read(0xAC), read(0xAD))
ac3 = signed_short(read(0xAE), read(0xAF))
ac4 = unsigned_short(read(0xB0), read(0xB1))
ac5 = unsigned_short(read(0xB2), read(0xB3))
ac6 = unsigned_short(read(0xB4),read(0xB5))
b1 = signed_short(read(0xB6), read(0xB7))
b2 = signed_short(read(0xB8), read(0xB9))
mb = signed_short(read(0xBA), read(0xBB))
mc = signed_short(read(0xBC), read(0xBD))
md = signed_short(read(0xBE), read(0xBF))

while True:
    # read uncompensated temperature value

    write(0xF4, 0x2E)
    time.sleep(0.005)
    ut = (read(0xF6) << 8) | read(0xF7)

    # read uncompensated pressure value

    write(0xF4, 0x34 + (oss << 6))
    time.sleep(0.005)
    up = ((((read(0xF6) << 8) | read(0xF7)) << 8) | read(0xF8)) >> (8 - oss)

    # calculate true temperature

    x1 = ((ut - ac6)*ac5) / (2**15)
    x2 = (mc * (2**11)) / (x1 + md)
    b5 = x1 + x2
    t = (b5 + 8) / (2**4)
    # temperature in 0.1 C to temperature in C
    t = t / 10

    # calculate true pressure

    b6 = b5 - 4000
    x1 = (b2 * (b6 * b6 / (2**12))) / (2**11)
    x2 = (ac2 * b6) / (2**11)
    x3 = x1 + x2
    b3 = ((int(ac1*4 + x3) << oss) + 2) / 4
    x1 = ac3 * b6 / (2**13)
    x2 = (b1 * (b6 * b6 / (2**12))) / (2**16)
    x3 = ((x1 + x2) + 2) / (2**2)
    b4 = ac4 * (x3 + 32768) / (2**15)
    b7 = (up - b3) * (50000 >> oss)
    p = 0
    if b7 < 0x80000000:
        p = (b7 * 2) / b4
    else:
        p = (b7 / b4) * 2
    x1 = (p / (2**8)) ** 2
    x1 = (x1 * 3038) / (2**16)
    x2 = (-7357 * p) / (2**16)
    p = p + (x1 + x2 + 3791) / (2**4)

    # pascal to millimeter of mercury
    p = p*0.00750062

    print("t = {:.1f} C, p = {:.1f} mmHg".format(t, p))
    time.sleep(1)