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<HTML
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><HEAD
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><TITLE
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>Communication Protocol</TITLE
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"><LINK
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HREF="ecos-ref.html"><LINK
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REL="UP"
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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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>eCos Reference Manual</TH
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><HR
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WIDTH="100%"></DIV
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><H1
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><A
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NAME="USBSETH-PROTOCOL">Communication Protocol</H1
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><DIV
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CLASS="REFNAMEDIV"
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><A
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NAME="AEN17632"
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></A
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><H2
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>Name</H2
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>Communication Protocol -- Protocol used between the host-side device driver and the eCos
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USB-ethernet package </DIV
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><DIV
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CLASS="REFSECT1"
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><A
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NAME="AEN17635"
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></A
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><H2
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>Description</H2
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><P
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>There is a USB standard for the protocol to be used between the host
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and a class of communication devices, including ethernet. However, the
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eCos USB-ethernet package does not implement this protocol: the target
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hardware for which the package was first developed had certain
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limitations, and could not implement the standard. Instead, the package
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implements a simple new protocol.</P
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><P
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>A USB-ethernet peripheral involves bulk transfers on two endpoints:
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one endpoint will be used for packets from host to peripheral and the
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other will be used for the opposite direction. Transfers in both
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directions are variable length, with a lower limit of 16 bytes and an
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upper limit of 1516 bytes. The first two bytes of each transfer
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constitute a header specific to USB-ethernet. The next 14 bytes form
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the normal header for an ethernet frame: destination MAC address,
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source MAC address, and a protocol field. The remaining data, up to
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1500 bytes, are the payload. The first two bytes give the size of the
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ethernet frame, least significant byte first, with a value between 14
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and 1514.</P
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><P
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>For example an ARP request from host to peripheral involves an
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ethernet frame of 42 bytes (0x002A), with the usual 14-byte header and
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a 28-byte payload. The destination is the broadcast address
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0xFFFFFFFFFFFF. The source depends on the MAC address specified for
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the host in the call to <A
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HREF="usbseth-init.html"
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><TT
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CLASS="FUNCTION"
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>usbs_eth_init</TT
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></A
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>, e.g.
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0x405D90A9BC02. The remaining data is as specified by the appropriate
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<A
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HREF="http://www.ietf.org"
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TARGET="_top"
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>IETF RFC's</A
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>. The actual bulk
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USB transfer involves the following sequence of 44 bytes:</P
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><TABLE
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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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>2a 00 ff ff ff ff ff ff 40 5d 90 a9 bc 02 08 06
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00 01 08 00 06 04 00 01 40 5d 90 a9 bc 02 0a 00
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00 01 00 00 00 00 00 00 0a 00 00 02</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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>In addition there are two control messages. These will be sent by the
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host to endpoint 0, the control endpoint, and by default they will
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be handled by <A
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HREF="usbseth-control.html"
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><TT
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CLASS="FUNCTION"
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>usbs_eth_class_control_handler</TT
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></A
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>. If class-specific
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control messages are intercepted by other code then it is the
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responsibility of that code to invoke the USB-ethernet handler when
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appropriate.</P
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><P
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>The first control message can be used by the host to obtain a MAC
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address:</P
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><TABLE
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><TD
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><PRE
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CLASS="PROGRAMLISTING"
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>#define ECOS_USBETH_CONTROL_GET_MAC_ADDRESS 0x01</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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>The control message's type field should specify IN as the direction.
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The request field should be <TT
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CLASS="LITERAL"
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>0x01</TT
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>. The length fields
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should specify a size of 6 bytes. The remaining fields of the control
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message will be ignored by the USB-ethernet package. The response
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consists of the 6-byte MAC address supplied by the initialization call
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<A
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HREF="usbseth-init.html"
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><TT
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CLASS="FUNCTION"
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>usbs_eth_init</TT
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></A
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>.</P
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><P
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>The second control message can be used by the host to enable or
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disable promiscuous mode.</P
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><TABLE
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><PRE
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CLASS="PROGRAMLISTING"
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>#define ECOS_USBETH_CONTROL_SET_PROMISCUOUS_MODE 0x02</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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>This control message involves no further data so the length field
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should be set to 0. The value field should be non-zero to enable
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promiscuous mode, zero to disable it. The request field should be
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<TT
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CLASS="LITERAL"
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>0x02</TT
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>. The remaining fields in the control message
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will be ignored. It is the responsibility of the host-side device
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driver to keep track of whether or not promiscuous mode is currently
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enabled. It will be disabled when the peripheral changes to
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Configured state, typically at the point where the host-side device
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driver has been activated.</P
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>Example Host-side Device Driver</TD
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