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<!-- Copyright (C) 2003 Red Hat, Inc.                                -->
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>USB-ethernet State Handling</TITLE
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><H1
><A
NAME="USBSETH-CONTROL">USB-ethernet State Handling</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN17514"
></A
><H2
>Name</H2
>USB-ethernet State Handling&nbsp;--&nbsp;Maintaining the USB-ethernet connection with the host</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN17517"><H2
>Synopsis</H2
><DIV
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NAME="AEN17518"><P
></P
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><TD
><PRE
CLASS="FUNCSYNOPSISINFO"
>#include &lt;cyg/io/usb/usbs_eth.h&gt;</PRE
></TD
></TR
></TABLE
><P
><CODE
><CODE
CLASS="FUNCDEF"
>usbs_control_return usbs_eth_class_control_handler</CODE
>(usbs_control_endpoint* ep0, void* callback_data);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>void usbs_eth_state_change_handler</CODE
>(usbs_control_endpoint* ep0, void* callback_data, usbs_state_change change, int old_state);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>void usbs_eth_disable</CODE
>(usbs_eth* usbseth&#62;);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>void usbs_eth_enable</CODE
>(usbs_eth* usbseth&#62;);</CODE
></P
><P
></P
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN17548"
></A
><H2
>Description</H2
><P
>When the USB-ethernet package is initialized by a call to <A
HREF="usbseth-init.html"
><TT
CLASS="FUNCTION"
>usbs_eth_init</TT
></A
> it
installs <TT
CLASS="FUNCTION"
>usbs_eth_state_change_handler</TT
> to handle
USB state changes. This allows the package to detect when the
connection between the host and the peripheral is established or
broken, resulting in internal calls to
<TT
CLASS="FUNCTION"
>usbs_eth_enable</TT
> and
<TT
CLASS="FUNCTION"
>usbs_eth_disable</TT
> respectively. This is
appropriate if no other code needs to access the USB device. However,
if there is other code, either other USB-related packages or the
application itself, that needs to perform I/O over the USB bus, then
typically the USB-ethernet package should not have exclusive access to
state change events. Instead, the assumption is that higher-level
code, typically provided by the application, will install an
alternative state change handler in the control endpoint data
structure after the call to <TT
CLASS="FUNCTION"
>usbs_eth_init</TT
>. This
alternative handler will either chain into
<TT
CLASS="FUNCTION"
>usbs_eth_state_change_handler</TT
> when appropriate,
or else it will invoke <TT
CLASS="FUNCTION"
>usbs_eth_enable</TT
> and
<TT
CLASS="FUNCTION"
>usbs_eth_disable</TT
> directly. For further details of
state change handlers and control endpoints generally, see the
documentation for the common USB-slave package.</P
><P
>Similarly, <TT
CLASS="FUNCTION"
>usbs_eth_init</TT
> will install
<TT
CLASS="FUNCTION"
>usbs_eth_class_control_handler</TT
> in the control
endpoint data structure as the appropriate handler for class-specific
USB control messages. This code will handle the ethernet-specific
<A
HREF="usbseth-protocol.html"
>control messages </A
>, for example
requests by the host to enable or disable promiscuous mode or to
obtain the MAC address. If the USB device is not shared with any other
code then this is both necessary and sufficient. However, if other code
is involved and if that code also needs to process certain control
messages, higher-level code should install its own handler and chain
to the USB-ethernet one when appropriate. It should be noted that the
request code is encoded in just a single byte, so there is a real
possibility that exactly the same number will be used by different
protocols for different requests. Any such problems will have to be
identified and resolved by application developers, and may involve
modifying the source code for the USB-ethernet package.</P
><P
>As an alternative to chaining the state change handler, higher-level
code can instead call <TT
CLASS="FUNCTION"
>usbs_eth_disable</TT
> and
<TT
CLASS="FUNCTION"
>usbs_eth_enable</TT
> directly. These functions may
also be called if the USB-ethernet package should become inactive for
reasons not related directly to events on the USB bus. The main effect
of <TT
CLASS="FUNCTION"
>usbs_eth_enable</TT
> is to restart receive
operations and to allow transmits. The main effect of
<TT
CLASS="FUNCTION"
>usbs_eth_disable</TT
> is to block further transmits:
any current receive operations need to be aborted at the USB level,
for example by halting the appropriate endpoint.</P
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