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          TCP/IP Networking for eCos

          now provides a complete

          TCP/IP networking stack,

based on a snapshot of the FreeBSD code, released by the

KAME project.

The networking support is

          fully featured and well tested within the eCos environment.

Since this networking package is based on BSD code, it is

very complete and robust.  The eCos implementation includes support

for the following protocols:   

IPv4

UDP

TCP

ICMP

raw packet interface

Multi-cast addressing

IPv6 (including UDP, ICP, ICMP)

These additional features are also present in the package,

        but are not supported:

Berkeley Packet Filter   

Uni-cast support   

Multi-cast routing   

This document describes how to get started with the Freebsd

TCP/IP network stack. 

A number of ethernet devices may be supported. The default configuration

supports two instances of the interface by default,

and you will need to write your own driver instantiation code,

and supplemental startup and initialization code,

if you should add additional ones.

The target for your board will normally be supplied with an

ethernet driver, in which case including the network stack and

generic ethernet driver package to your build will automatically

enable usage of the ethernet device driver.

If your target is not supplied with an ethernet

driver, you will need to use loopback (see

).

Using the Build->Packages dialog,

add the packages “Networking”,

“Freebsd TCP/IP Stack”

and “Common Ethernet Support”

to your configuration.  Their package names

are CYGPKG_NET, CYGPKG_NET_FREEBSD_STACK and CYGPKG_NET_ETH_DRIVERS

respectively.

A short-cut way to do this is by

using the “net” template

if it is available for your platform.

The platform-specific ethernet device driver for your platform

will be added as part of the target selection (in the

Build->Templates “Hardware” item),

along with the

PCI I/O subsystem (if relevent) and the appropriate serial device driver.

For example, the PowerPC MBX target selection adds the package

PKG_NET_QUICC_ETH_DRIVERS,

and the Cirrus Logic EDB7xxx target selection adds the package

CYGPKG_NET_EDB7XXX_ETH_DRIVERS.

After this, eCos and its tests can be built exactly as usual.

By default, most of the network tests are not built.  This

is because some of them require manual intervention, i.e. they are

to be run “by hand”, and are not suitable for

automated testing.  To build the full set of network tests, set

the configuration option CYGPKG_NET_BUILD_TESTS “Build

networking tests (demo programs)” within “Networking

support build options”.

The APIs for the standard networking calls such as

socket(), recv() and so on, are

in header files relative to the top-level

include directory, within the standard subdirectories as conventionally

found in /usr/include.  For example:

 install/include/arpa/tftp.h

 install/include/netinet/tcpip.h

 install/include/sys/socket.h

 install/include/sys/socketvar.h

 install/include/sys/sockio.h

network.h at the top level

defines various extensions, for example the API

init_all_network_interfaces(void)

described

above.  We advise including network.h whether

you use these features or not.

In general, using the networking code may require definition

of two symbols: _KERNEL and __ECOS.  _KERNEL

is not normally required; __ECOS is normally required.

So add this to your compile lines for files which use the network

stack:

        -D__ECOS

To expand a little, it’s like this because this is

a port of a standard distribution external to eCos.  One goal

is to perturb the sources as little as possible, so that upgrading

and maintenance from the external distribution is simplified.  The __ECOS

symbol marks out the eCos additions in making the port.

The _KERNEL symbol is traditional UNIX practice: it distinguishes

a compilation which is to be linked into the kernel from one which

is part of an application.  eCos applications are fully linked,

so this distinction does not apply.  _KERNEL can however

be used to control the visibility of the internals of the stack,

so depending on what features your application uses, it may or may

not be necessary.

The include file network.h undefines _KERNEL

unconditionally, to provide an application-like compilation environment.

If you were writing code which, for example,

enumerates the stack’s internal

structures, that is a kernel-like compilation environment, so you

would need to define _KERNEL (in addition to __ECOS)

and avoid including network.h.

The network stack supports an extension to the standard select

semantics which allows all threads that are waiting to be restarted

even if the select conditions are not satisfied.

The standard select() API:  

int

select(int nfd,

       fd_set *in, fd_set *out, fd_set *ex,

       struct timeval *tv); 

does not support the restart.

The additional API:  

int

cyg_select_with_abort(int nfd,

       fd_set *in, fd_set *out, fd_set *ex,

       struct timeval *tv)

behaves exactly as select() with the additional feature that

a call to

void cyg_select_abort(void)

will cause all threads waiting in any

cyg_select_with_abort() call

to cease waiting and continue execution.

The FreeBSD stack starts up with IPv4 support in an essentially

"disabled" state.  It requires the application to take positive actions

to assign IPv4 address and routes before the interfaces will respond

to packets from the outside world.

This is not true of IPv6 support.  If IPv6 support was enabled in the

eCos build, the stack will start up with link-local addresses

assigned and interfaces listening to certain multicast addresses.  The

stack will not only respond to IPv6 packets, it will spontaneously

send IPv6 packets without actions from application code.

If an eCos application wishes to disable IPv6 support at runtime, the

decision has to be made very early in the boot process and actions

taken to prevent the invocation of IPv6 startup code in the network

stack.  This involves two rather obscure "tricks":

Using a dummy device driver's "init" hook as a place to execute some

code early in the startup process

 Monkey-patching the network stack's table of

initializers by looping through it and checking the function pointers

against certain globally visible symbols and replacing the two

IPv6-specific function pointers with pointers to a "noop" function.

The code listing below shows an example of disabling IPv6 support at

runtime if the global variable we_want_to_disable_ipv6 is non-zero.

The assumption is that some code in the HAL initialization or

somewhere else has made the decision whether or not to disable IPv6

support and set that variable accordingly.

// Sample code showing a method of disabling IPv6 support at runtime

// Do-nothing function we can patch into the network stack's init table

// when we want to disable one of the entries

static void

init_noop(void *dummy)

{

}

// Function that loops through the network stack's init table and

// disables the two IPv6 entries

static void

disable_ipv6(void)

{

    extern struct init_tab_entry __NET_INIT_TAB__[],

                    __NET_INIT_TAB_END__;

    struct init_tab_entry *init_entry;

    extern void     cyg_net_add_domain(void *);

    extern void     ip6_init2(void *);

    extern char     inet6domain[];

    for (init_entry = __NET_INIT_TAB__; init_entry != &__NET_INIT_TAB_END__;

         init_entry++)

        if ((init_entry->fun == ip6_init2)

            || (init_entry->fun == cyg_net_add_domain

                && init_entry->data == (void *)inet6domain))

            init_entry->fun = init_noop;

}

// Function called early in the inintialization process via a dummy

// device table entry

static bool

early_init(struct cyg_devtab_entry *tab)

{

    if (we_want_to_disable_ipv6)

        disable_ipv6();

    return 0;

}

// Dummy device driver table entry that will call the above early_init()

// function during the startup process

DEVTAB_ENTRY(device_master_early_init,

             "neveruse",

             NULL,

             NULL,

             early_init,

             NULL,

             NULL

    );