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# Source code for pywws.device_pyusb

    """Low level USB interface to weather station, using PyUSB.

    Introduction
    ============

    This module handles low level communication with the weather station
    via the `PyUSB <http://sourceforge.net/apps/trac/pyusb/>`_ library. An
    alternative module, :doc:`pywws.device_cython_hidapi`, uses the
    `cython-hidapi <https://github.com/gbishop/cython-hidapi>`_ library.
    The choice of which module to use depends on which libraries are
    available for you computer.

    Users of recent versions of Mac OS have no choice. The operating
    system makes it very difficult to access HID devices (such as the
    weather station) directly, so the ``hidapi`` library has to be used.
    ``cython-hidapi`` is a Python interface to that library.

    Users of OpenWRT and similar embedded Linux platforms will probably
    not be able to install ``cython-hidapi``, so are constrained to use
    ``libusb`` and its ``PyUSB`` Python interface.

    Installation
    ============

    Some of this software may already be installed on your machine, so do
    check before downloading sources and compiling them yourself.

    #.  Install libusb and PyUSB.

        These should be available as packages for your operating system,
        but their names may vary. For example, on Ubuntu Linux::

            sudo apt-get install libusb-0.1 python-usb

        On some embedded linux systems::

            ipkg install libusb py25-usb

    Testing
    =======

    Run ``TestWeatherStation.py`` with increased verbosity so it reports
    which USB device access module is being used::

        python TestWeatherStation.py -vv
        18:28:09:pywws.WeatherStation.CUSBDrive:using pywws.device_pyusb
        0000 55 aa ff ff ff ff ff ff ff ff ff ff ff ff ff ff 05 20 01 41 11 00 00 00 81 00 00 0f 05 00 e0 51
        0020 03 27 ce 27 00 00 00 00 00 00 00 12 02 14 18 27 41 23 c8 00 00 00 46 2d 2c 01 64 80 c8 00 00 00
        0040 64 00 64 80 a0 28 80 25 a0 28 80 25 03 36 00 05 6b 00 00 0a 00 f4 01 12 00 00 00 00 00 00 00 00
        0060 00 00 49 0a 63 12 05 01 7f 00 36 01 60 80 36 01 60 80 bc 00 7b 80 95 28 12 26 6c 28 25 26 c8 01
        0080 1d 02 d8 00 de 00 ff 00 ff 00 ff 00 00 11 10 06 01 29 12 02 01 19 32 11 09 09 05 18 12 01 22 13
        00a0 14 11 11 04 15 04 11 12 17 05 12 11 09 02 15 26 12 02 11 07 05 11 09 02 15 26 12 02 11 07 05 11
        00c0 09 10 09 12 12 02 02 12 38 12 02 07 19 00 11 12 16 03 27 12 02 03 11 00 11 12 16 03 27 11 12 26
        00e0 21 32 11 12 26 21 32 12 02 06 19 57 12 02 06 19 57 12 02 06 19 57 12 02 06 19 57 12 02 06 19 57

    API
    ===

    """

    __docformat__ = "restructuredtext en"

    import platform
    import usb

    class USBDevice(object):
        def __init__(self, idVendor, idProduct):
            """Low level USB device access via PyUSB library.

            :param idVendor: the USB ``vendor ID` number, for example 0x1941.

            :type idVendor: int

            :param idProduct: the USB ``product ID` number, for example 0x8021.

            :type idProduct: int

            """
            dev = self._find_device(idVendor, idProduct)
            if not dev:
                raise IOError("Weather station device not found")
            self.devh = dev.open()
            if not self.devh:
                raise IOError("Open device failed")
    ##        if platform.system() is 'Windows':
    ##            self.devh.setConfiguration(1)
            try:
                self.devh.claimInterface(0)
            except usb.USBError:
                # claim interface failed, try detaching kernel driver first
                if not hasattr(self.devh, 'detachKernelDriver'):
                    raise RuntimeError(
                        "Please upgrade pyusb (or python-usb) to 0.4 or higher")
                try:
                    self.devh.detachKernelDriver(0)
                    self.devh.claimInterface(0)
                except usb.USBError:
                    raise IOError("Claim interface failed")
            # device may have data left over from an incomplete read
            for i in range(4):
                try:
                    self.devh.interruptRead(0x81, 8, 1200)
                except usb.USBError:
                    break

        def __del__(self):
            if self.devh:
                try:
                    self.devh.releaseInterface()
                except usb.USBError:
                    # interface was not claimed. No problem
                    pass

        def _find_device(self, idVendor, idProduct):
            """Find a USB device by product and vendor id."""
            for bus in usb.busses():
                for device in bus.devices:
                    if (device.idVendor == idVendor and
                        device.idProduct == idProduct):
                        return device
            return None

        def read_data(self, size):
            """Receive data from the device.

            If the read fails for any reason, an :obj:`IOError` exception
            is raised.

            :param size: the number of bytes to read.

            :type size: int

            :return: the data received.

            :rtype: list(int)

            """
            result = self.devh.interruptRead(0x81, size, 1200)
            if result is None or len(result) < size:
                raise IOError('pywws.device_libusb.USBDevice.read_data failed')
            return list(result)

        def write_data(self, buf):
            """Send data to the device.

            If the write fails for any reason, an :obj:`IOError` exception
            is raised.

            :param buf: the data to send.

            :type buf: list(int)

            :return: success status.

            :rtype: bool

            """
            result = self.devh.controlMsg(
                usb.ENDPOINT_OUT + usb.TYPE_CLASS + usb.RECIP_INTERFACE,
                usb.REQ_SET_CONFIGURATION, buf, value=0x200, timeout=50)
            if result != len(buf):
                raise IOError('pywws.device_libusb.USBDevice.write_data failed')
            return True

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