#!/usr/bin/python
  
  import smbus
  
  # ===========================================================================
  # Adafruit_I2C Class
  # ===========================================================================
  
  class Adafruit_I2C(object):
  
    @staticmethod
    def getPiRevision():
      "Gets the version number of the Raspberry Pi board"
      # Courtesy quick2wire-python-api
      # https://github.com/quick2wire/quick2wire-python-api
      # Updated revision info from: http://elinux.org/RPi_HardwareHistory#Board_Revision_History
      try:
        with open('/proc/cpuinfo','r') as f:
          for line in f:
            if line.startswith('Revision'):
              return 1 if line.rstrip()[-1] in ['2','3'] else 2
      except:
        return 0
  
    @staticmethod
    def getPiI2CBusNumber():
      # Gets the I2C bus number /dev/i2c#
      return 1 if Adafruit_I2C.getPiRevision() > 1 else 0
  
    def __init__(self, address, busnum=-1, debug=False):
      self.address = address
      # By default, the correct I2C bus is auto-detected using /proc/cpuinfo
      # Alternatively, you can hard-code the bus version below:
      # self.bus = smbus.SMBus(0); # Force I2C0 (early 256MB Pi's)
      # self.bus = smbus.SMBus(1); # Force I2C1 (512MB Pi's)
      self.bus = smbus.SMBus(busnum)# if busnum >= 0 else Adafruit_I2C.getPiI2CBusNumber())
      self.debug = debug
  
    def reverseByteOrder(self, data):
      "Reverses the byte order of an int (16-bit) or long (32-bit) value"
      # Courtesy Vishal Sapre
      byteCount = len(hex(data)[2:].replace('L','')[::2])
      val       = 0
      for i in range(byteCount):
        val    = (val << 8) | (data & 0xff)
        data >>= 8
      return val
  
    def errMsg(self):
      print("Error accessing 0x%02X: Check your I2C address" % self.address)
      return -1
  
    def write8(self, reg, value):
      "Writes an 8-bit value to the specified register/address"
      try:
        self.bus.write_byte_data(self.address, reg, value)
        if self.debug:
          print("I2C: Wrote 0x%02X to register 0x%02X" % (value, reg))
      except IOError as err:
        return self.errMsg()
  
    def write16(self, reg, value):
      "Writes a 16-bit value to the specified register/address pair"
      try:
        self.bus.write_word_data(self.address, reg, value)
        if self.debug:
          print (("I2C: Wrote 0x%02X to register pair 0x%02X,0x%02X" % (value, reg, reg+1)))
      except IOError as err:
        return self.errMsg()
  
    def writeRaw8(self, value):
      "Writes an 8-bit value on the bus"
      try:
        self.bus.write_byte(self.address, value)
        if self.debug:
          print("I2C: Wrote 0x%02X" % value)
      except IOError as err:
        return self.errMsg()
  
    def writeList(self, reg, list):
      "Writes an array of bytes using I2C format"
      try:
        if self.debug:
          print("I2C: Writing list to register 0x%02X:" % reg)
          print(list)
        self.bus.write_i2c_block_data(self.address, reg, list)
      except IOError as err:
        return self.errMsg()
  
    def readList(self, reg, length):
      "Read a list of bytes from the I2C device"
      try:
        results = self.bus.read_i2c_block_data(self.address, reg, length)
        if self.debug:
          print(("I2C: Device 0x%02X returned the following from reg 0x%02X" %
           (self.address, reg)))
          print(results)
        return results
      except IOError as err:
        return self.errMsg()
  
    def readU8(self, reg):
      "Read an unsigned byte from the I2C device"
      try:
        result = self.bus.read_byte_data(self.address, reg)
        if self.debug:
          print(("I2C: Device 0x%02X returned 0x%02X from reg 0x%02X" %
           (self.address, result & 0xFF, reg)))
        return result
      except IOError as err:
        return self.errMsg()
  
    def readS8(self, reg):
      "Reads a signed byte from the I2C device"
      try:
        result = self.bus.read_byte_data(self.address, reg)
        if result > 127: result -= 256
        if self.debug:
          print(("I2C: Device 0x%02X returned 0x%02X from reg 0x%02X" %
           (self.address, result & 0xFF, reg)))
        return result
      except IOError as err:
        return self.errMsg()
  
    def readU16(self, reg, little_endian=True):
      "Reads an unsigned 16-bit value from the I2C device"
      try:
        result = self.bus.read_word_data(self.address,reg)
        # Swap bytes if using big endian because read_word_data assumes little 
        # endian on ARM (little endian) systems.
        if not little_endian:
          result = ((result << 8) & 0xFF00) + (result >> 8)
        if (self.debug):
          print("I2C: Device 0x%02X returned 0x%04X from reg 0x%02X" % (self.address, result & 0xFFFF, reg))
        return result
      except IOError as err:
        return self.errMsg()
  
    def readS16(self, reg, little_endian=True):
      "Reads a signed 16-bit value from the I2C device"
      try:
        result = self.readU16(reg,little_endian)
        if result > 32767: result -= 65536
        return result
      except IOError as err:
        return self.errMsg()
  
  if __name__ == '__main__':
    try:
      bus = Adafruit_I2C(address=0x60)
      print("Default I2C bus is accessible")
    except:
      print("Error accessing default I2C bus")