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<!-- Date:        2001/01/13                                         -->
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<reference id="io-usb-slave-eth">
  <title>eCos Support for Developing USB-ethernet Peripherals</title>

<!-- {{{ Intro                          -->

<refentry id="usbseth-intro">
<refmeta>
<refentrytitle>Introduction</refentrytitle>
</refmeta>
<refnamediv>
<refname>Introduction</refname>
<refpurpose>eCos support for developing USB ethernet peripherals</refpurpose>
</refnamediv>

<refsect1><title>Introduction</title>
<para>
The eCos USB-ethernet package provides additional support for USB
peripherals that involve some sort of ethernet-style network. This can
be a traditional ethernet, or it can involve some other networking
technology that uses ethernet frames as a unit of transfer. It
provides functions to transfer ethernet frames over the USB bus,
handles certain control messages from the host, and optionally it can
provide a network device driver for use by the eCos TCP/IP stack.
The package comes with an example host-side device driver.
</para>
<para>
The USB-ethernet package is not tied to any specific hardware. It
requires the presence of USB hardware and a suitable device driver,
but not all USB peripherals involve ethernet communications. Hence the
configuration system cannot load the package automatically for
specific targets, in the way that a USB device driver or an ethernet
driver can be loaded automatically. Instead, the package has to be
added explicitly. When using the command line tools this will involve
an operation like the following:
</para>
<screen width=72 format=linespecific>
$ ecosconfig add usbs_eth
</screen>
<para>
Typically, this will automatically cause the USB device driver to
become active. Loading the USB-ethernet package automatically provides
functionality for <link linkend="usbseth-init">initialization</link>,
<link linkend="usbseth-data">data transfer</link>, and the handling of
<link linkend="usbseth-control">control messages</link> and state
changes. If the current configuration includes the eCos TCP/IP stack
then the <link linkend="usbseth-netdev">network device driver</link>
support will be enabled as well by default, allowing the stack to
exchange ethernet frames over the USB bus.
</para>
<para>
There is a USB standard for a class of communication devices including
ethernet. The package does not implement this standard, due to
limitations in the hardware for which the package was first developed.
Instead, the package uses its own <link
linkend="usbseth-protocol">protocol</link> between USB
<link linkend="usbseth-host">host device driver</link> and the
peripheral. 
</para>
</refsect1>

<refsect1><title id="usbseth-intro-scenarios">Usage Scenarios</title>
<para>
The USB-ethernet package can be used several different scenarios. In
a simple scenario, the peripheral serves only to connect the USB host
to a suitable network:
</para>
<informalfigure PgWide=1>
<mediaobject>
<imageobject>
<imagedata fileref="simple.eps" format="eps" Scalefit=1 Align="Center">
</imageobject>
<imageobject>
<imagedata fileref="simple.gif" format="gif" Align="Center">
</imageobject>
</mediaobject>
</informalfigure>
<para>
After initialization, and once the USB connection between host and
peripheral has been established, higher-level code needs to detect
packets that are intended for the host, and to forward these. This can
be achieved by the low-level <function>usbs_eth_start_tx</function>
function. Similarly, higher-level code needs to detect packets coming
from the host, using <function>usbs_eth_start_rx</function>, and to
forward these using the real network. As far as the host is concerned
it is connected directly to the network. In this scenario there is no
confusion about addresses: there is a single MAC address for the
host/peripheral combination, corresponding to the connection to the
real network, and it is this address which should be supplied during
<link linkend="usbseth-init">initialization</link>.
</para>
<para>
In a more complicated scenario, there is a TCP/IP stack running inside
the peripheral.
</para>
<informalfigure PgWide=1>
<mediaobject>
<imageobject>
<imagedata fileref="tcpip.eps" format="eps" Scalefit=1 Align="Center">
</imageobject>
<imageobject>
<imagedata fileref="tcpip.gif" format="gif" Align="Center">
</imageobject>
</mediaobject>
</informalfigure>
<para>
This involves the USB-ethernet package providing a service both to the
host and to the eCos TCP/IP stack. It achieves the latter by acting as
an eCos network device. Typically, the TCP/IP stack will be configured
to act as a network bridge. The USB peripheral needs to examine the
packets arriving over the real network. Some of these packets will be
intended for the host, while others will be intended for the
peripheral itself. To distinguish between these two scenarios, two
distinct MAC addresses are needed: one for the host, and one for the
peripheral. Similarly, packets sent by the host may have to be
forwarded via the real network, or they may be intended for the TCP/IP
stack inside the peripheral. Packets generated inside the peripheral's
TCP/IP stack may need to be sent via the real network or over the USB
bus. The network bridge software will have to take care of all these
possibilities. Unusually for a network bridge, one of the network
segments being bridged will only ever have one machine attached.
</para>
<para>
There are other possible usage scenarios. For example, the peripheral
might not be attached to a real network at all. Instead it could be
the USB host that acts as a network bridge, allowing a TCP/IP stack
inside the peripheral to communicate with the outside world. The
various details will depend on the exact type of peripheral being
developed. 
</para>
</refsect1>
</refentry>

<!-- }}} -->
<!-- {{{ Initialization                 -->

<refentry id="usbseth-init">
<refmeta>
<refentrytitle>Initializing the USB-ethernet Package</refentrytitle>
</refmeta>
<refnamediv>
<refname><function>usbs_eth_init</function></refname>
<refpurpose>Initializing the USB-ethernet Package</refpurpose>
</refnamediv>

<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>
#include &lt;cyg/io/usb/usbs_eth.h&gt;
</funcsynopsisinfo>	
<funcprototype>
<funcdef>void <function>usbs_eth_init</function></funcdef>
<paramdef>usbs_eth* <parameter>usbeth</parameter></paramdef>
<paramdef>usbs_control_endpoint* <parameter>ep0</parameter></paramdef>
<paramdef>usbs_rx_endpoint* <parameter>ep1</parameter></paramdef>
<paramdef>usbs_tx_endpoint* <parameter>ep2</parameter></paramdef>
<paramdef>unsigned char* <parameter>mac_address</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>

<refsect1><title>Description</title>
<para>
The USB-ethernet package is not tied to any specific hardware. It
requires certain functionality: there must be USB-slave hardware
supported by a device driver; there must also be two endpoints for
bulk transfers between host and peripheral, one for each direction;
there must also be a control endpoint, although of course that is
implicit with any USB hardware.
</para>
<para>
However, USB-slave hardware may well provide more endpoints than the
minimum required for ethernet support. Some of those endpoints might
be used by other packages, while other endpoints might be used
directly by the application, or might not be needed for the peripheral
being built. There is also the possibility of a USB peripheral that
supports multiple configurations, with the ethernet support active in
only some of those configurations. The USB-ethernet package has no
knowledge about any of this, so it relies on higher-level code to tell
it which endpoints should be used and other information. This is the
purpose of the <function>usbs_eth_init</function> function.
</para>
<para>
The first argument identifies the specific
<structname>usbs_eth</structname> data structure that is affected. It
is expected that the vast majority of affected applications will only
provide a single USB-ethernet device to a single host, and the package
automatically provides a suitable data structure
<literal>usbs_eth0</literal> to support this. If multiple
<structname>usbs_eth</structname> structures are needed for some
reason then these need to be instantiated by other code, and each one
needs to be initialised by a call to
<function>usbs_eth_init()</function>. 
</para>
<para>
The next three arguments identify the endpoints that should be used
for USB communications: a control endpoint, a receive endpoint for
ethernet packets coming from the host to the peripheral, and a
transmit endpoint for ethernet packets going in the other direction.
Obviously all three endpoints should be provided by the same USB
hardware. The USB-ethernet package assumes that it has sole access to
the receive and transmit endpoints, subject to the use of
<function>usbs_eth_disable</function> and
<function>usbs_eth_enable</function> control functions. The package
also assumes that no other code is interested in USB state changes or
class control messages: it installs handlers
<link linkend="usbseth-control"><function>usbs_eth_state_change_handler</function></link>
and
<link linkend="usbseth-control"><function>usbs_eth_class_control_handler</function></link>
in the control endpoint. If any other code does need to handle USB
state changes or class control messages then replacement handlers
should be installed after the call to
<function>usbs_eth_init</function>, and those replacements should
invoke the USB-ethernet ones when appropriate.
</para>
<para>
The final argument to <function>usbs_eth_init</function> specifies 
the MAC address (or Ethernet Station Address) that should be provided
to the host-side device driver. Since the USB-ethernet package does not
interact directly with a real ethernet device it cannot obtain the MAC
address from any hardware. Instead, it must be supplied by higher-level
code. The details depend on the <link
linkend="usbseth-intro-scenarios">scenario</link> in which the
USB-ethernet package is being used.
</para>
<para>
The call to <function>usbs_eth_init</function> should normally happen
after the enumeration data has been provided but before the underlying
USB device driver has been started. If the USB device were to be
started first then a connection between host and peripheral could be
established immediately, and the host-side device driver would attempt
to contact the USB-ethernet package for information such as the MAC
address. 
</para>
<programlisting width=72>
int
main(int argc, char** argv)
{
    unsigned char host_MAC[6] = { 0x40, 0x5d, 0x90, 0xa9, 0xbc, 0x02 };

    usbs_sa11x0_ep0.enumeration_data    = &amp;usb_enum_data;
    &hellip;
    usbs_eth_init(&amp;usbs_eth0, &amp;usbs_sa11x0_ep0, &amp;usbs_sa11x0_ep1, &amp;usbs_sa11x0_ep2, host_MAC);
    &hellip;
    usbs_start(&amp;usbs_sa11x0_ep0);
    &hellip;
}
</programlisting>
</refsect1>

</refentry>

<!-- }}} -->
<!-- {{{ Data Transfer                  -->

<refentry id="usbseth-data">
<refmeta>
<refentrytitle>USB-ethernet Data Transfers</refentrytitle>
</refmeta>
<refnamediv>
<refname>USB-ethernet Data Transfers</refname>
<refpurpose>Exchanging ethernet packets with the USB host</refpurpose>
</refnamediv>

<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>
#include &lt;cyg/io/usb/usbs_eth.h&gt;
</funcsynopsisinfo>	

<funcprototype>
<funcdef>void <function>usbs_eth_start_rx</function></funcdef>
<paramdef>usbs_eth* <parameter>usbseth</parameter></paramdef>
<paramdef>unsigned char* <parameter>buffer</parameter></paramdef>
<paramdef>void (*)(usbs_eth*, void*, int) <parameter>complete_fn</parameter></paramdef>
<paramdef>void* <parameter>complete_data</parameter></paramdef>
</funcprototype>

<funcprototype>
<funcdef>void <function>usbs_eth_start_tx</function></funcdef>
<paramdef>usbs_eth* <parameter>usbseth</parameter></paramdef>
<paramdef>unsigned char* <parameter>buffer</parameter></paramdef>
<paramdef>void (*)(usbs_eth*, void*, int) <parameter>complete_fn</parameter></paramdef>
<paramdef>void* <parameter>complete_data</parameter></paramdef>
</funcprototype>

</funcsynopsis>
</refsynopsisdiv>

<refsect1><title>Description</title>
<para>
The USB-ethernet package provides two main modes of operation. In the
first mode it provides a <link linkend="usbseth-netdev">network device
driver</link> for use by a TCP/IP stack running inside the USB
peripheral. All incoming ethernet packages should be passed up the
TCP/IP stack, and only the stack will generate outgoing packets. Apart
from <link linkend="usbseth-init">initialization</link> and possibly
certain <link linkend="usbseth-control">control operations</link>,
higher-level code will not interact with the USB-ethernet package
directly.
</para>
<para>
In the second mode there is no TCP/IP stack running inside the USB
peripheral. For example, a simple USB-ethernet converter has an
ethernet chip and a USB port: ethernet packets received by the
ethernet chip need to be forwarded to the USB host, and ethernet
packets sent by the USB host need to be sent out of the ethernet chip.
<function>usbs_eth_start_rx</function> and
<function>usbs_eth_start_tx</function> allow for this lower-level
access to the USB-ethernet package.
</para>
<para>
The two modes of operation are mutually exclusive. If the network
device driver mode is enabled then application code should communicate
at the TCP/IP level, and not by using the lower-level functions.
Instead, it is the network device driver that will make use of these
functions, and it assumes that it has exclusive access. The package
does not perform any locking.
</para>
<para>
The transmit and receive functions work in much the same way. The
first argument identifies the <structname>usbs_eth</structname>
structure that should be used. For the majority of applications this
will be <literal>usbs_eth0</literal>. The second argument specifies
the location of the ethernet packet; outgoing for
<function>usbs_eth_start_tx</function> and incoming for
<function>usbs_eth_start_rx</function>. This buffer should correspond
to the <link linkend="usbseth-protocol">protocol</link>:
</para>
<orderedlist>
<listitem>
<para>
Outgoing packets can consist of up to 1516 bytes, consisting of a
two-byte header specific to USB-ethernet followed by a standard
ethernet frame (a header with 6-byte destination address, 6-byte
source address and a further two bytes, followed by a payload of
up to 1500 bytes). The two-byte USB-ethernet header consists simply of
the size of the ethernet frame, i.e. the size of the rest of the
packet not including the USB-ethernet header, with the least
significant byte first.
</para>
</listitem>
<listitem>
<para>
For incoming packets the supplied buffer should usually be at least
1516 bytes. There may be special circumstances in which a smaller
buffer might be safe; for example, if the host-side device driver is
modified to support only smaller packets. Once the packet has been
received the buffer will contain a two-byte header specific to
USB-ethernet, followed by a normal ethernet frame. The header
gives the size of the ethernet frame, excluding the header, with the
least significant byte first.
</para>
</listitem>
</orderedlist>
<para>
Both <function>usbs_eth_start_tx</function> and
<function>usbs_eth_start_rx</function> are asynchronous: the transfer
is started and, some time later, a completion function will be invoked.
The third and fourth arguments to both
<function>usbs_eth_start_tx</function> and
<function>usbs_eth_start_rx</function> supply the completion function
and an argument to that function respectively. The completion function
will be invoked with three arguments: a pointer to the
<structname>usbs_eth</structname> data structure, usually
<literal>usbs_eth0</literal>; the supplied completion data ; and a
return code field. A negative value indicates that an error occurred,
for example <literal>-EPIPE</literal> if the connection between USB
host and peripheral has been broken, or <literal>-EAGAIN</literal> if
an endpoint has been halted. A positive value indicates the total size
of the transfer, which should correspond to the size in the
USB-ethernet header plus an additional two bytes for the header
itself.
</para>
<para>
If the data transfer is succesful then the completion function will
typically be invoked in DSR context rather than in thread context,
although this depends on the implementation of the underlying USB
device driver. Therefore the completion function is restricted in what
it can do; in particular, it must not make any calls that will or may
block such as locking a mutex or allocating memory. The kernel
documentation should be consulted for more details of DSR's and
interrupt handling generally. Note that if the transfer finishes
quickly then the completion function may be invoked before
<function>usbs_eth_start_rx</function> or
<function>usbs_eth_start_tx</function> returns. This is especially
likely to happen if the current thread is descheduled after starting
the data transfer but before returning from these functions.
</para>
<para>
For transmit operations, it is possible for
<function>usbs_eth_start_tx</function> to invoke the completion
function immediately. If there is no current connection between host
and target then the transmit will fail immediately with
<literal>-EPIPE</literal>. In addition the USB-ethernet package will
check the destination MAC address and make sure that the ethernet
frame really is intended for the host: either it must be for the
address specified in the initialization call <link
linkend="usbseth-init"><function>usbs_eth_init</function></link>, or
it must be a broadcast packet, or the host must have enabled
promiscuous mode. 
</para>
</refsect1>

</refentry>

<!-- }}} -->
<!-- {{{ State and Control Messages     -->

<refentry id="usbseth-control">
<refmeta>
<refentrytitle>USB-ethernet State Handling</refentrytitle>
</refmeta>
<refnamediv>
<refname>USB-ethernet State Handling</refname>
<refpurpose>Maintaining the USB-ethernet connection with the host</refpurpose>
</refnamediv>

<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>
#include &lt;cyg/io/usb/usbs_eth.h&gt;
</funcsynopsisinfo>	

<funcprototype>
<funcdef>usbs_control_return <function>usbs_eth_class_control_handler</function></funcdef>
<paramdef>usbs_control_endpoint* <parameter>ep0</parameter></paramdef>
<paramdef>void* <parameter>callback_data</parameter></paramdef>
</funcprototype>

<funcprototype>
<funcdef>void <function>usbs_eth_state_change_handler</function></funcdef>
<paramdef>usbs_control_endpoint* <parameter>ep0</parameter></paramdef>
<paramdef>void* <parameter>callback_data</parameter></paramdef>
<paramdef>usbs_state_change <parameter>change</parameter></paramdef>
<paramdef>int <parameter>old_state</parameter></paramdef>
</funcprototype>

<funcprototype>
<funcdef>void <function>usbs_eth_disable</function></funcdef>
<paramdef>usbs_eth* <parameter>usbseth></parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>void <function>usbs_eth_enable</function></funcdef>
<paramdef>usbs_eth* <parameter>usbseth></parameter></paramdef>
</funcprototype>

</funcsynopsis>
</refsynopsisdiv>

<refsect1><title>Description</title>
<para>
When the USB-ethernet package is initialized by a call to <link
linkend="usbseth-init"><function>usbs_eth_init</function></link> it
installs <function>usbs_eth_state_change_handler</function> 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
<function>usbs_eth_enable</function> and
<function>usbs_eth_disable</function> 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 <function>usbs_eth_init</function>. This
alternative handler will either chain into
<function>usbs_eth_state_change_handler</function> when appropriate,
or else it will invoke <function>usbs_eth_enable</function> and
<function>usbs_eth_disable</function> directly. For further details of
state change handlers and control endpoints generally, see the
documentation for the common USB-slave package.
</para>
<para>
Similarly, <function>usbs_eth_init</function> will install
<function>usbs_eth_class_control_handler</function> in the control
endpoint data structure as the appropriate handler for class-specific
USB control messages. This code will handle the ethernet-specific
<link linkend="usbseth-protocol">control messages </link>, 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.
</para>
<para>
As an alternative to chaining the state change handler, higher-level
code can instead call <function>usbs_eth_disable</function> and
<function>usbs_eth_enable</function> 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 <function>usbs_eth_enable</function> is to restart receive
operations and to allow transmits. The main effect of
<function>usbs_eth_disable</function> is to block further transmits:
any current receive operations need to be aborted at the USB level,
for example by halting the appropriate endpoint.
</para>
</refsect1>

</refentry>

<!-- }}} -->
<!-- {{{ netdev device                  -->

<refentry id="usbseth-netdev">
<refmeta>
<refentrytitle>Network Device for the eCos TCP/IP Stack</refentrytitle>
</refmeta>
<refnamediv>
<refname>Network Device</refname>
<refpurpose>USB-ethernet support for the eCos TCP/IP Stack</refpurpose>
</refnamediv>

<refsect1><title>Description</title>
<para>
If the USB peripheral involves running the eCos TCP/IP stack and that
stack needs to use USB-ethernet as a transport layer (or as one of the
transports), then the USB-ethernet package can provide a suitable
network device driver. It is still necessary for higher-level code to
perform appropriate initialization by calling <link
linkend="usbseth-init"><function>usbs_eth_init</function></link>, but
after that it will be the TCP/IP stack rather than application code
that transmits or receives ethernet frames.
</para>
<para>
Not all peripherals involving the USB-ethernet package will require a
TCP/IP stack. Hence the provision of the network device is controlled
by a configuration option <literal>CYGPKG_USBS_ETHDRV</literal>. By
default this will be enabled if the TCP/IP package
<literal>CYGPKG_NET</literal> is loaded, and disabled otherwise. 
</para>
<para>
There are a number of other configuration options related to the
network device. <literal>CYGFUN_USBS_ETHDRV_STATISTICS</literal>
determines whether or not the package will maintain statistics, mainly
intended for SNMP: by default this will be enabled if the SNMP support
package <literal>CYGPKG_SNMPAGENT</literal> is loaded, and disabled
otherwise. The name of the ethernet device is controlled by
<literal>CYGDATA_USBS_ETHDRV_NAME</literal>, and has a default value
of either <literal>eth0</literal> or <literal>eth1</literal>
depending on whether or not there is another network device driver
present in the configuration.
</para>
<para>
Usually eCos network device drivers default to using DHCP for
obtaining necessary information such as IP addresses. This is not
appropriate for USB-ethernet devices. On the host-side the
USB-ethernet network device will not exist until the USB peripheral
has been plugged in and communication has been established. Therefore
any DHCP daemon on the host would not be listening on that network
device at the point that eCos requests its IP and other information. A
related issue is that the use of DHCP would imply the presence of a
DHCP daemon on every affected host machine, as opposed to a single
daemon (plus backups) for the network as a whole. For these reasons
the USB-ethernet package precludes the use of DHCP as a way of setting
the IP address, instead requiring alternatives such as manual
configuration.
</para>
</refsect1>

</refentry>

<!-- }}} -->
<!-- {{{ ecos_usbeth                    -->

<refentry id="usbseth-host">
<refmeta>
<refentrytitle>Example Host-side Device Driver</refentrytitle>
</refmeta>
<refnamediv>
<refname>Example Host-side Device Driver</refname>
<refpurpose>Provide host-side support for the eCos USB-ethernet package</refpurpose>
</refnamediv>

<refsect1><title>Description</title>
<para>
The USB-ethernet package is supplied with a single host-side device
driver. This driver has been developed against the Linux kernel
2.2.16-22, as shipped with Red Hat 7. The driver is provided as is and
should not be considered production quality: for example it only
checks for a bogus vendor id <literal>0x4242</literal> rather than an
official vendor id supplied by the <ulink
url="http://www.usb.org/">USB Implementers Forum</ulink>. Also, if the
peripheral involves multiple configurations or multiple interfaces, it
will fail to detect this. However, the driver can be used for simple
testing and as the basis of a full device driver. Details of the
protocol used between host and peripheral can be found in the <link
linkend="usbseth-protocol">Communication Protocol</link> section.
</para>
<para>
The host-side device driver can be found in the <filename
class="directory">host</filename> subdirectory of the USB-ethernet
package, specifically the file <filename>ecos_usbeth.c</filename>, and
comes with a <filename>Makefile</filename>. Both files may need
to be modified for specific applications. For example, the vendor id
table <literal>ecos_usbeth_implementations</literal> may need to be
updated for the specific USB peripheral being built. The
<filename>Makefile</filename> assumes that the Linux kernel sources
reside in <filename class="directory">/usr/src/linux</filename>, and
that the kernel has already been configured and built. Assuming this
is the case, the device driver can be built simply by invoking
<command>make</command> with no additional arguments. This will result
in a dynamically loadable kernel module,
<filename>ecos_usbeth.o</filename>, in the current directory.
</para>
<note>
<para>
As normal for Linux kernel builds, the generated files such as
<filename>ecos_usbeth.o</filename> live in the same directory as the
source tree. This is very different from eCos where the source tree
(or component repository) is kept separate from any builds. There may
be problems if the component repository is kept read-only or if it is
put under source code control. Any such problems can be avoided by
making a copy of the <filename class="directory">host</filename>
subdirectory and building that copy.
</para>
</note>
<para>
Loading the kernel module into the current system requires root
privileges. If the generic USB support is also a loadable module and
has not been loaded already, this must happen first:
</para>
<screen width=72 format=linespecific>
# insmod usb-uhci
Using /lib/modules/2.2.16-22/usb/usb-uhci.o
</screen>
<para>
Depending on the host hardware, the <literal>uhci</literal> or
<literal>usb-ohci</literal> modules may be more appropriate. Loading
the generic USB module will typically result in a number of messages
to the logfile <filename>/var/log/messages</filename>, giving details
of the specific host-side hardware that has been detected plus any
hubs. The next step is to load the USB-ethernet module:
</para>
<screen width=72 format=linespecific>
# insmod ecos_usbeth.o
</screen>
<para>
This should result in a number of additional diagnostics in the
logfile:
</para>
<screen width=72 format=linespecific>
Apr 1 18:01:08 grumpy kernel: eCos USB-ethernet device driver
Apr 1 18:01:08 grumpy kernel: usb.c: registered new driver ecos_usbeth
</screen>
<para>
If a suitable USB peripheral is now connected the host will detect
this, assign an address in the local USB network, obtain enumeration
data, and find a suitable device driver. Assuming the peripheral and
device driver agree on the supported vendor ids, the
<filename>ecos_usbeth.o</filename> module will be selected and this
will be reported in the system log:
</para>
<screen width=86 format=linespecific>
Apr 1 18:04:12 grumpy kernel: usb.c: USB new device connect, assigned device number 3
Apr 1 18:04:12 grumpy kernel: eCos-based USB ethernet peripheral active at eth1
</screen>
<para>
What can happen next depends very much on the software that is running
on top of the USB-ethernet package inside the peripheral. For example,
if there is a TCP/IP stack then it should be possible to bring up a
network connection between host and peripheral using
<command>ifconfig</command>.
</para>
</refsect1>

</refentry>

<!-- }}} -->
<!-- {{{ Protocol                       -->

<refentry id="usbseth-protocol">
<refmeta>
<refentrytitle>Communication Protocol</refentrytitle>
</refmeta>
<refnamediv>
<refname>Communication Protocol</refname>
<refpurpose>Protocol used between the host-side device driver and the eCos
USB-ethernet package </refpurpose>
</refnamediv>

<refsect1><title>Description</title>
<para>
There is a USB standard for the protocol to be used between the host
and a class of communication devices, including ethernet. However, the
eCos USB-ethernet package does not implement this protocol: the target
hardware for which the package was first developed had certain
limitations, and could not implement the standard. Instead, the package
implements a simple new protocol.
</para>
<para>
A USB-ethernet peripheral involves bulk transfers on two endpoints:
one endpoint will be used for packets from host to peripheral and the
other will be used for the opposite direction. Transfers in both
directions are variable length, with a lower limit of 16 bytes and an
upper limit of 1516 bytes. The first two bytes of each transfer
constitute a header specific to USB-ethernet. The next 14 bytes form
the normal header for an ethernet frame: destination MAC address,
source MAC address, and a protocol field. The remaining data, up to
1500 bytes, are the payload. The first two bytes give the size of the
ethernet frame, least significant byte first, with a value between 14
and 1514.
</para>
<para>
For example an ARP request from host to peripheral involves an
ethernet frame of 42 bytes (0x002A), with the usual 14-byte header and
a 28-byte payload. The destination is the broadcast address
0xFFFFFFFFFFFF. The source depends on the MAC address specified for
the host in the call to <link
linkend="usbseth-init"><function>usbs_eth_init</function></link>, e.g.
0x405D90A9BC02. The remaining data is as specified by the appropriate
<ulink url="http://www.ietf.org">IETF RFC's</ulink>. The actual bulk
USB transfer involves the following sequence of 44 bytes:
</para>
<screen width=72 format=linespecific>
2a 00 ff ff ff ff ff ff 40 5d 90 a9 bc 02 08 06
00 01 08 00 06 04 00 01 40 5d 90 a9 bc 02 0a 00
00 01 00 00 00 00 00 00 0a 00 00 02
</screen>
<para>
In addition there are two control messages. These will be sent by the
host to endpoint 0, the control endpoint, and by default they will
be handled by <link linkend="usbseth-control"><function>
usbs_eth_class_control_handler</function></link>. If class-specific
control messages are intercepted by other code then it is the
responsibility of that code to invoke the USB-ethernet handler when
appropriate.
</para>
<para>
The first control message can be used by the host to obtain a MAC
address:
</para>
<programlisting width=72>
#define ECOS_USBETH_CONTROL_GET_MAC_ADDRESS         0x01
</programlisting>
<para>
The control message's type field should specify IN as the direction.
The request field should be <literal>0x01</literal>. The length fields
should specify a size of 6 bytes. The remaining fields of the control
message will be ignored by the USB-ethernet package. The response
consists of the 6-byte MAC address supplied by the initialization call
<link
linkend="usbseth-init"><function>usbs_eth_init</function></link>.
</para>
<para>
The second control message can be used by the host to enable or
disable promiscuous mode.
</para>
<programlisting width=72>
#define ECOS_USBETH_CONTROL_SET_PROMISCUOUS_MODE    0x02
</programlisting>
<para>
This control message involves no further data so the length field
should be set to 0. The value field should be non-zero to enable
promiscuous mode, zero to disable it. The request field should be
<literal>0x02</literal>. The remaining fields in the control message
will be ignored. It is the responsibility of the host-side device
driver to keep track of whether or not promiscuous mode is currently
enabled. It will be disabled when the peripheral changes to
Configured state, typically at the point where the host-side device
driver has been activated.
</para>
</refsect1>

</refentry>

<!-- }}} -->

</reference>
