Temperature Sensor Board with ZIO

"""Reading Temperature using ZIO and Temperature Sensor Board

temp_sense.py - Script to read temperature and display on stdout
Refer SA56004x data sheet for register descriptions
"""
import zio
import sys
from time import sleep

#Slave address
TEMP_SENSOR = 0x90 >> 1
#Read Manufacturer ID
REG_RMID = 0xFE
#Configuration register
REG_CON = 0x09
#Alert Mode register
REG_AM = 0xBF
#Status Register
REG_SR = 0x02
#Local Temperature high byte register
REG_LTHB = 0x00
#Temote Temperature high byte register
REG_RTHB = 0x01
#Status of sensor
DIODE_OPEN = 2
#Variable to read LOCAL Temperature
TEMP_LOCAL = 0
#Variable to read Remote Temperature
TEMP_REMOTE = 1


def i2c_set_reg8(i2c, dev, reg, value):
    """Write an 8-bit value to a slave device register.

    Args:
        i2c: I2C slave device object
        dev: Slave device register address
        reg: Register address
        value: Value to be written to the slave register
    """
    i2c.write(dev, [reg, value])
    return


def i2c_get_reg8(i2c, dev, reg):
    """Read an 8-bit value from a slave device register.

    Args:
        i2c: I2C slave device object
        dev: I2C slave address
        reg: Register address

    Returns:
        int, a byte Read from the device
    """
    rx = i2c.write_read(dev, [reg], 1)
    return rx[0]


def temperature_init(i2c):
    """Initialize the Temperature Sensor.

    Read the manufacturer ID by which
    we can know the slave device is working.

    Args:
        i2c: I2C Slave device object

    Returns:
        int, Returns integer 0 on success and -1 on failure
    """
    global TEMP_SENSOR, REG_RMID
    i2c.config(100)
    ide = i2c_get_reg8(i2c, TEMP_SENSOR, REG_RMID)
    if ide != 0xA1:
        return -1

    return 0


def temperature_read(i2c, sensor):
    """Read the temperature from the Temperature Sensor

    Args:
        i2c: I2C slave device object
        sensor: Local sensor or remote sensor values

    Returns:
        If the sensor is LOCAL then return local temperature
        highbyte. Else it will return remote sensor high byte
        If there is no remote sensor connected it will return None.
    """
    global TEMP_LOCAL

    if sensor == TEMP_LOCAL:
        return i2c_get_reg8(i2c, TEMP_SENSOR, REG_LTHB)
    else:
        status = i2c_get_reg8(i2c, TEMP_SENSOR, REG_SR)
        if status & DIODE_OPEN:
            return None

        return i2c_get_reg8(i2c, TEMP_SENSOR, REG_LTHB)

    return None


def main():
    global TEMP_LOCAL
    global temp
    agent = zio.Agent("/dev/ttyACM0")
    i2c = zio.I2C(agent)
    ret = temperature_init(i2c)
    if ret != 0:
        print "Temperature SensorInitialize error"
        sys.exit(1)

    while True:
        tem = temperature_read(i2c, TEMP_LOCAL)
        if  tem is None:
            print "Read Error"
            sys.exit(1)

        sys.stdout.write("Temperature is %02d\r" % tem)
        sys.stdout.flush()
        sleep(1)

if __name__ == '__main__':
    try:
        main()
    except KeyboardInterrupt:
        print "KeboardInterrupt"
        sys.exit(1)
    except zio.I2CNoAckError, error:
        print error
        sys.exit(1)