Adafruit_I2C.py

#!/usr/bin/python
# NOTE!! This code is from the Adafruit Learning System articles on the Raspberry Pi (http://learn.adafruit.com/) 
# The original version of the code can be found in the Adafruit Raspberry Pi Python Library on Github at  https://github.com/adafruit/Adafruit-Raspberry-Pi-Python-Code

# ===========================================================================
# Adafruit_I2C Base Class
# ===========================================================================

class Adafruit_I2C :

  def __init__(self, address, busnum = 3, debug=False):
    try:
      import smbus
      self.bus = smbus.SMBus(busnum)
    except ImportError:
      self.bus=None

    self.address = address
    self.debug = debug

  def reverseByteOrder(self, data):
    "Reverses the byte order of an int (16-bit) or long (32-bit) value"
    # Courtesy Vishal Sapre
    dstr = hex(data)[2:].replace('L','')
    byteCount = len(dstr[::2])
    val = 0
    for i, n in enumerate(range(byteCount)):
      d = data & 0xFF
      val |= (d << (8 * (byteCount - i - 1)))
      data >>= 8
    return val

  def write8(self, reg, value):
    "Writes an 8-bit value to the specified register/address"

    if self.bus is None:
      return -1

    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, err:
      print "Error accessing 0x%02X: Check your I2C address" % self.address
      return -1

  def writeList(self, reg, list):
    "Writes an array of bytes using I2C format"

    if self.bus is None:
      return -1

    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, err:
      print "Error accessing 0x%02X: Check your I2C address" % self.address
      return -1

  def readList(self, reg, length):
    "Read a list of bytes from the I2C device"

    if self.bus is None:
      return -1

    results = []
    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, err:
      print "Error accessing 09x%02X: Check your I2C address" % self.address
      return -1

  def readU8(self, reg):
    "Read an unsigned byte from the I2C device"

    if self.bus is None:
      return -1

    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, err:
      print "Error accessing 0x%02X: Check your I2C address" % self.address
      return -1

  def readS8(self, reg):
    "Reads a signed byte from the I2C device"

    if self.bus is None:
      return -1

    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)
      if (result > 127):
        return result - 256
      else:
        return result
    except IOError, err:
      print "Error accessing 0x%02X: Check your I2C address" % self.address
      return -1

  def readU16(self, reg):
    "Reads an unsigned 16-bit value from the I2C device"

    if self.bus is None:
      return -1

    try:
      hibyte = self.bus.read_byte_data(self.address, reg)
      result = (hibyte << 8) + self.bus.read_byte_data(self.address, reg+1)
      if (self.debug):
        print "I2C: Device 0x%02X returned 0x%04X from reg 0x%02X" % (self.address, result & 0xFFFF, reg)
      return result
    except IOError, err:
      print "Error accessing 0x%02X: Check your I2C address" % self.address
      return -1

  def readS16(self, reg):
    "Reads a signed 16-bit value from the I2C device"

    if self.bus is None:
      return -1

    try:
      hibyte = self.bus.read_byte_data(self.address, reg)
      if (hibyte > 127):
        hibyte -= 256
      result = (hibyte << 8) + self.bus.read_byte_data(self.address, reg+1)
      if (self.debug):
        print "I2C: Device 0x%02X returned 0x%04X from reg 0x%02X" % (self.address, result & 0xFFFF, reg)
      return result
    except IOError, err:
      print "Error accessing 0x%02X: Check your I2C address" % self.address
      return -1