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<!-- Copyright (C) 2001 Red Hat, Inc. -->
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<!-- permission is obtained from the copyright holder. -->
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<HTML
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><HEAD
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><TITLE
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>Introduction</TITLE
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><META
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.64
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"><LINK
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REL="HOME"
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TITLE="eCos Support for Developing USB-ethernet Peripherals"
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HREF="io-usb-slave-eth.html"><LINK
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REL="PREVIOUS"
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TITLE="eCos Support for Developing USB-ethernet Peripherals"
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HREF="io-usb-slave-eth.html"><LINK
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REL="NEXT"
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TITLE="Initializing the USB-ethernet Package"
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HREF="usbseth-init.html"></HEAD
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><BODY
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><TR
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><TH
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COLSPAN="3"
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ALIGN="center"
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>eCos Support for Developing USB-ethernet Peripherals</TH
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></TR
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><TR
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><TD
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WIDTH="10%"
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ALIGN="left"
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VALIGN="bottom"
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><A
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HREF="io-usb-slave-eth.html"
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>Prev</A
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></TD
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><TD
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WIDTH="80%"
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><TD
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WIDTH="10%"
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ALIGN="right"
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VALIGN="bottom"
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><A
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HREF="usbseth-init.html"
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>Next</A
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></TD
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></TR
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></TABLE
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><HR
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ALIGN="LEFT"
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WIDTH="100%"></DIV
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><H1
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><A
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NAME="USBSETH-INTRO"
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>Introduction</A
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></H1
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><DIV
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CLASS="REFNAMEDIV"
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><A
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NAME="AEN6"
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></A
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><H2
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>Name</H2
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>Introduction -- eCos support for developing USB ethernet peripherals</DIV
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><DIV
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CLASS="REFSECT1"
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><A
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NAME="AEN9"
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></A
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><H2
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>Introduction</H2
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><P
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>The eCos USB-ethernet package provides additional support for USB
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peripherals that involve some sort of ethernet-style network. This can
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be a traditional ethernet, or it can involve some other networking
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technology that uses ethernet frames as a unit of transfer. It
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provides functions to transfer ethernet frames over the USB bus,
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handles certain control messages from the host, and optionally it can
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provide a network device driver for use by the eCos TCP/IP stack.
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The package comes with an example host-side device driver.</P
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><P
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>The USB-ethernet package is not tied to any specific hardware. It
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requires the presence of USB hardware and a suitable device driver,
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but not all USB peripherals involve ethernet communications. Hence the
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configuration system cannot load the package automatically for
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specific targets, in the way that a USB device driver or an ethernet
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driver can be loaded automatically. Instead, the package has to be
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added explicitly. When using the command line tools this will involve
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an operation like the following:</P
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><TABLE
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BORDER="0"
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><TR
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><TD
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><PRE
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CLASS="SCREEN"
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>$ ecosconfig add usbs_eth</PRE
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></TD
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></TR
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></TABLE
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><P
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>Typically, this will automatically cause the USB device driver to
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become active. Loading the USB-ethernet package automatically provides
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functionality for <A
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HREF="usbseth-init.html"
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>initialization</A
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>,
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<A
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HREF="usbseth-data.html"
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>data transfer</A
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>, and the handling of
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<A
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HREF="usbseth-control.html"
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>control messages</A
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> and state
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changes. If the current configuration includes the eCos TCP/IP stack
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then the <A
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HREF="usbseth-netdev.html"
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>network device driver</A
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>
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support will be enabled as well by default, allowing the stack to
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exchange ethernet frames over the USB bus.</P
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><P
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>There is a USB standard for a class of communication devices including
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ethernet. The package does not implement this standard, due to
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limitations in the hardware for which the package was first developed.
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Instead, the package uses its own <A
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HREF="usbseth-protocol.html"
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>protocol</A
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> between USB
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<A
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HREF="usbseth-host.html"
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>host device driver</A
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> and the
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peripheral. </P
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></DIV
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><DIV
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CLASS="REFSECT1"
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><A
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NAME="AEN22"
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></A
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><H2
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>Usage Scenarios</H2
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><P
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>The USB-ethernet package can be used several different scenarios. In
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a simple scenario, the peripheral serves only to connect the USB host
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to a suitable network:</P
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><DIV
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CLASS="INFORMALFIGURE"
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><A
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NAME="AEN25"
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></A
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><P
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></P
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><DIV
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><P
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><IMG
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SRC="simple.gif"
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></IMG
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></P
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></DIV
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><P
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></P
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></DIV
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><P
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>After initialization, and once the USB connection between host and
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peripheral has been established, higher-level code needs to detect
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packets that are intended for the host, and to forward these. This can
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be achieved by the low-level <TT
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CLASS="FUNCTION"
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>usbs_eth_start_tx</TT
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>
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function. Similarly, higher-level code needs to detect packets coming
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from the host, using <TT
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CLASS="FUNCTION"
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>usbs_eth_start_rx</TT
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>, and to
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forward these using the real network. As far as the host is concerned
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it is connected directly to the network. In this scenario there is no
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confusion about addresses: there is a single MAC address for the
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host/peripheral combination, corresponding to the connection to the
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real network, and it is this address which should be supplied during
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<A
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HREF="usbseth-init.html"
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>initialization</A
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>.</P
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><P
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>In a more complicated scenario, there is a TCP/IP stack running inside
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the peripheral.</P
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><DIV
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CLASS="INFORMALFIGURE"
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><A
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NAME="AEN36"
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></A
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><P
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></P
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><DIV
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CLASS="MEDIAOBJECT"
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><P
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><IMG
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SRC="tcpip.gif"
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></IMG
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></P
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></DIV
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><P
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></P
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></DIV
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><P
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>This involves the USB-ethernet package providing a service both to the
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host and to the eCos TCP/IP stack. It achieves the latter by acting as
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an eCos network device. Typically, the TCP/IP stack will be configured
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to act as a network bridge. The USB peripheral needs to examine the
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packets arriving over the real network. Some of these packets will be
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intended for the host, while others will be intended for the
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peripheral itself. To distinguish between these two scenarios, two
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distinct MAC addresses are needed: one for the host, and one for the
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peripheral. Similarly, packets sent by the host may have to be
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forwarded via the real network, or they may be intended for the TCP/IP
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stack inside the peripheral. Packets generated inside the peripheral's
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TCP/IP stack may need to be sent via the real network or over the USB
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bus. The network bridge software will have to take care of all these
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possibilities. Unusually for a network bridge, one of the network
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segments being bridged will only ever have one machine attached.</P
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><P
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>There are other possible usage scenarios. For example, the peripheral
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might not be attached to a real network at all. Instead it could be
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the USB host that acts as a network bridge, allowing a TCP/IP stack
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inside the peripheral to communicate with the outside world. The
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various details will depend on the exact type of peripheral being
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developed. </P
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><A
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HREF="io-usb-slave-eth.html"
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>Prev</A
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></TD
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><TD
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WIDTH="34%"
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><A
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HREF="io-usb-slave-eth.html"
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>Home</A
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></TD
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><TD
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WIDTH="33%"
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ALIGN="right"
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VALIGN="top"
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><A
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HREF="usbseth-init.html"
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>Next</A
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></TD
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></TR
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><TR
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WIDTH="33%"
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ALIGN="left"
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VALIGN="top"
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>eCos Support for Developing USB-ethernet Peripherals</TD
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><TD
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WIDTH="34%"
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ALIGN="center"
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> </TD
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WIDTH="33%"
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ALIGN="right"
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VALIGN="top"
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>Initializing the USB-ethernet Package</TD
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></TR
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></TABLE
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></DIV
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></HTML
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>
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