stdd/adafruit_7segment/i2c.py

# -*- coding: utf-8-*-
#
# This file is part of stdd, the simple time display daemon,
# written by Helmut Pozimski <helmut@pozimski.eu>,
# licensed under the 3-clause BSD license
# This file was originally written by Written by Limor Fried, Kevin Townsend
# and Mikey Sklar for Adafruit Industries. BSD license,
# all text above must be included in any redistribution

"""
===========================================================================
AdafruitI2c Class
===========================================================================
"""

from __future__ import print_function

from smbus import SMBus


class AdafruitI2c(object):
    """ This class provides low level i2c access.
    """
    @staticmethod
    def get_pi_revision():
        """Gets the version number of the Raspberry Pi board"""
        # Courtesy quick2wire-python-api
        # https://github.com/quick2wire/quick2wire-python-api
        try:
            with open('/proc/cpuinfo', 'r') as file_obj:
                for line in file_obj:
                    if line.startswith('Revision'):
                        return 1 if line.rstrip()[-1] in ['1', '2'] else 2
        except IOError:
            return 0

    @staticmethod
    def get_pi_i2c_bus_number():
        """ Gets the I2C bus number /dev/i2c# """
        return 1 if AdafruitI2c.get_pi_revision() > 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(
            busnum if busnum >= 0 else AdafruitI2c.get_pi_i2c_bus_number())
        self.debug = debug

    @staticmethod
    def reverse_byte_order(data):
        """Reverses the byte order of an int (16-bit) or long (32-bit) value"""
        # Courtesy Vishal Sapre
        byte_count = len(hex(data)[2:].replace('L', '')[::2])
        val = 0
        for i in range(byte_count):
            val = (val << 8) | (data & 0xff)
            data >>= 8
        return val

    @staticmethod
    def err_msg():
        """Raises an exception."""
        raise Exception("cannot connect to device, check hardware address!")

    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:
            return self.err_msg()

    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:
            return self.err_msg()

    def write_list(self, reg, w_list):
        """Writes an array of bytes using I2C format"""
        try:
            if self.debug:
                print("I2C: Writing list to register 0x%02X:" % reg)
                print(w_list)
            self.bus.write_i2c_block_data(self.address, reg, w_list)
        except IOError:
            return self.err_msg()

    def read_list(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:
            return self.err_msg()

    def read_u8(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:
            return self.err_msg()

    def read_s8(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:
            return self.err_msg()

    def read_u16(self, reg):
        """Reads an unsigned 16-bit value from the I2C device"""
        try:
            hibyte = self.read_u8(reg)
            lobyte = self.read_u8(reg+1)
            result = (hibyte << 8) + lobyte
            if self.debug:
                print("I2C: Device 0x%02X returned 0x%04X from reg 0x%02X" % (
                    self.address, result & 0xFFFF, reg))
            return result
        except IOError:
            return self.err_msg()

    def read_s16(self, reg):
        """Reads a signed 16-bit value from the I2C device"""
        try:
            hibyte = self.read_s8(reg)
            lobyte = self.read_u8(reg+1)
            result = (hibyte << 8) + lobyte
            if self.debug:
                print("I2C: Device 0x%02X returned 0x%04X from reg 0x%02X" %
                      (self.address, result & 0xFFFF, reg))
            return result
        except IOError:
            return self.err_msg()

    def read_u16_rev(self, reg):
        """Reads an unsigned 16-bit value from the I2C device with rev byte
        order.
        """
        try:
            lobyte = self.read_u8(reg)
            hibyte = self.read_u8(reg+1)
            result = (hibyte << 8) + lobyte
            if self.debug:
                print("I2C: Device 0x%02X returned 0x%04X from reg 0x%02X" %
                      (self.address, result & 0xFFFF, reg))
            return result
        except IOError:
            return self.err_msg()

    def read_s16_rev(self, reg):
        """Reads a signed 16-bit value from the I2C device with rev byte
        order.
        """
        try:
            lobyte = self.read_s8(reg)
            hibyte = self.read_u8(reg+1)
            result = (hibyte << 8) + lobyte
            if self.debug:
                print("I2C: Device 0x%02X returned 0x%04X from reg 0x%02X" % (
                    self.address, result & 0xFFFF, reg))
            return result
        except IOError:
            return self.err_msg()

if __name__ == '__main__':
    try:
        BUS = AdafruitI2c(address=0)
        print("Default I2C bus is accessible")
    except:
        print("Error accessing default I2C bus")