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@c

@c  Written by Eric Norum

@c

@c  COPYRIGHT (c) 1988-2002.

@c  On-Line Applications Research Corporation (OAR).

@c  All rights reserved.

@c

@c  networkapp.t,v 1.16 2002/01/17 21:47:45 joel Exp

@c

@chapter Using Networking in an RTEMS Application

@section Makefile changes

@subsection Including the required managers

The FreeBSD networking code requires several RTEMS managers

in the application:

@example

MANAGERS = io event semaphore

@end example

@subsection Increasing the size of the heap

The networking tasks allocate a lot of memory.  For most applications

the heap should be at least 256 kbytes.

The amount of memory set aside for the heap can be adjusted by setting

the @code{CFLAGS_LD} definition as shown below:

@example

CFLAGS_LD += -Wl,--defsym -Wl,HeapSize=0x80000

@end example

This sets aside 512 kbytes of memory for the heap.

@section System Configuration

The networking tasks allocate some RTEMS objects.  These

must be accounted for in the application configuration table.  The following

lists the requirements.

@table @b

@item TASKS

One network task plus a receive and transmit task for each device.

@item SEMAPHORES

One network semaphore plus one syslog mutex semaphore if the application uses

openlog/syslog.

@item EVENTS

The network stack uses @code{RTEMS_EVENT_24} and @code{RTEMS_EVENT_25}.

This has no effect on the application configuration, but

application tasks which call the network functions should not

use these events for other purposes.

@end table

@section Initialization

@subsection Additional include files

The source file which declares the network configuration

structures and calls the network initialization function must include

@example

#include 

@end example

@subsection Network Configuration

The network configuration is specified by declaring

and initializing the @code{rtems_bsdnet_config}

structure.

@example

@group

struct rtems_bsdnet_config @{

  /*

   * This entry points to the head of the ifconfig chain.

   */

  struct rtems_bsdnet_ifconfig *ifconfig;

  /*

   * This entry should be rtems_bsdnet_do_bootp if BOOTP

   * is being used to configure the network, and NULL

   * if BOOTP is not being used.

   */

  void                    (*bootp)(void);

  /*

   * The remaining items can be initialized to 0, in

   * which case the default value will be used.

   */

  rtems_task_priority  network_task_priority;  /* 100        */

  unsigned long        mbuf_bytecount;         /* 64 kbytes  */

  unsigned long        mbuf_cluster_bytecount; /* 128 kbytes */

  char                *hostname;               /* BOOTP      */

  char                *domainname;             /* BOOTP      */

  char                *gateway;                /* BOOTP      */

  char                *log_host;               /* BOOTP      */

  char                *name_server[3];         /* BOOTP      */

  char                *ntp_server[3];          /* BOOTP      */

@};

@end group

@end example

The structure entries are described in the following table.

If your application uses BOOTP/DHCP to obtain network configuration

information and if you are happy with the default values described

below, you need to provide only the first two entries in this structure.

@table @code

@item struct rtems_bsdnet_ifconfig *ifconfig

A pointer to the first configuration structure of the first network

device.  This structure is described in the following section.

You must provide a value for this entry since there is no default value for it.

@item void (*bootp)(void)

This entry should be set to @code{rtems_bsdnet_do_bootp}

if your application will use BOOTP/DHCP

to obtain network configuration information.

It should be set to @code{NULL}

if your application does not use BOOTP/DHCP.

@item int network_task_priority

The priority at which the network task and network device

receive and transmit tasks will run.

If a value of 0 is specified the tasks will run at priority 100.

@item unsigned long mbuf_bytecount

The number of bytes to allocate from the heap for use as mbufs.

If a value of 0 is specified, 64 kbytes will be allocated.

@item unsigned long mbuf_cluster_bytecount

The number of bytes to allocate from the heap for use as mbuf clusters.

If a value of 0 is specified, 128 kbytes will be allocated.

@item char *hostname

The host name of the system.

If this, or any of the following, entries are @code{NULL} the value

may be obtained from a BOOTP/DHCP server.

@item char *domainname

The name of the Internet domain to which the system belongs.

@item char *gateway

The Internet host number of the network gateway machine,

specified in `dotted decimal' (@code{129.128.4.1}) form.

@item char *log_host

The Internet host number of the machine to which @code{syslog} messages

will be sent.

@item char *name_server[3]

The Internet host numbers of up to three machines to be used as

Internet Domain Name Servers.

@item char *ntp_server[3]

The Internet host numbers of up to three machines to be used as

Network Time Protocol (NTP) Servers.

@end table

In addition, the following fields in the @code{rtems_bsdnet_ifconfig}

are of interest.

@table @b

@item int port

The I/O port number (ex: 0x240) on which the external Ethernet

can be accessed.

@item int irno

The interrupt number of the external Ethernet controller.

@item int bpar

The address of the shared memory on the external Ethernet controller.

@end table

@subsection Network device configuration

Network devices are specified and configured by declaring and initializing a

@code{struct rtems_bsdnet_ifconfig} structure for each network device.

The structure entries are described in the following table.  An application

which uses a single network interface, gets network configuration information

from a BOOTP/DHCP server, and uses the default values for all driver

parameters needs to initialize only the first two entries in the

structure.

@table @code

@item char *name

The full name of the network device.  This name consists of the

driver name and the unit number (e.g. @code{"scc1"}).

The @code{bsp.h} include file usually defines RTEMS_BSP_NETWORK_DRIVER_NAME as

the name of the primary (or only) network driver.

@item int (*attach)(struct rtems_bsdnet_ifconfig *conf)

The address of the driver @code{attach} function.   The network

initialization function calls this function to configure the driver and

attach it to the network stack.

The @code{bsp.h} include file usually defines RTEMS_BSP_NETWORK_DRIVER_ATTACH as

the name of the  attach function of the primary (or only) network driver.

@item struct rtems_bsdnet_ifconfig *next

A pointer to the network device configuration structure for the next network

interface, or @code{NULL} if this is the configuration structure of the

last network interface.

@item char *ip_address

The Internet address of the device,

specified in `dotted decimal' (@code{129.128.4.2}) form, or @code{NULL}

if the device configuration information is being obtained from a

BOOTP/DHCP server.

@item char *ip_netmask

The Internet inetwork mask of the device,

specified in `dotted decimal' (@code{255.255.255.0}) form, or @code{NULL}

if the device configuration information is being obtained from a

BOOTP/DHCP server.

@item void *hardware_address

The hardware address of the device, or @code{NULL} if the driver is

to obtain the hardware address in some other way (usually  by reading

it from the device or from the bootstrap ROM).

@item int ignore_broadcast

Zero if the device is to accept broadcast packets, non-zero if the device

is to ignore broadcast packets.

@item int mtu

The maximum transmission unit of the device, or zero if the driver

is to choose a default value (typically 1500 for Ethernet devices).

@item int rbuf_count

The number of receive buffers to use, or zero if the driver is to

choose a default value

@item int xbuf_count

The number of transmit buffers to use, or zero if the driver is to

choose a default value

Keep in mind that some network devices may use 4 or more

transmit descriptors for a single transmit buffer.

@end table

A complete network configuration specification can be as simple as the one

shown in the following example.

This configuration uses a single network interface, gets

network configuration information

from a BOOTP/DHCP server, and uses the default values for all driver

parameters.

@example

static struct rtems_bsdnet_ifconfig netdriver_config = @{

        RTEMS_BSP_NETWORK_DRIVER_NAME,

        RTEMS_BSP_NETWORK_DRIVER_ATTACH

@};

struct rtems_bsdnet_config rtems_bsdnet_config = @{

        &netdriver_config,

        rtems_bsdnet_do_bootp,

@};

@end example

@subsection Network initialization

The networking tasks must be started before any network I/O operations

can be performed. This is done by calling:

@example

rtems_bsdnet_initialize_network ();

@end example

This function is declared in @code{rtems/rtems_bsdnet.h}.

t returns 0 on success and -1 on failure with an error code

in @code{errno}.  It is not possible to undo the effects of

a partial initialization, though, so the function can be

called only once irregardless of the return code.  Consequently,

if the condition for the failure can be corrected, the

system must be reset to permit another network initialization

attempt.

@section Application Programming Interface

The RTEMS network package provides almost a complete set of BSD network

services.  The network functions work like their BSD counterparts

with the following exceptions:

@itemize @bullet

@item A given socket can be read or written by only one task at a time.

@item The @code{select} function only works for file descriptors associated

with sockets.

@item You must call @code{openlog} before calling any of the @code{syslog} functions.

@item @b{Some of the network functions are not thread-safe.}

For example the following functions return a pointer to a static

buffer which remains valid only until the next call:

@table @code

@item gethostbyaddr

@item gethostbyname

@item inet_ntoa

(@code{inet_ntop} is thread-safe, though).

@end table

@item The RTEMS network package gathers statistics.

@item Addition of a mechanism to "tap onto" an interface

and monitor every packet received and transmitted.

@item Addition of @code{SO_SNDWAKEUP} and @code{SO_RCVWAKEUP} socket options.

@end itemize

Some of the new features are discussed in more detail in the following

sections.

@subsection Network Statistics

There are a number of functions to print statistics gathered by

the network stack.

These function are declared in @code{rtems/rtems_bsdnet.h}.

@table @code

@item rtems_bsdnet_show_if_stats

Display statistics gathered by network interfaces.

@item rtems_bsdnet_show_ip_stats

Display IP packet statistics.

@item rtems_bsdnet_show_icmp_stats

Display ICMP packet statistics.

@item rtems_bsdnet_show_tcp_stats

Display TCP packet statistics.

@item rtems_bsdnet_show_udp_stats

Display UDP packet statistics.

@item rtems_bsdnet_show_mbuf_stats

Display mbuf statistics.

@item rtems_bsdnet_show_inet_routes

Display the routing table.

@end table

@subsection Tapping Into an Interface

RTEMS add two new ioctls to the BSD networking code:

SIOCSIFTAP and SIOCGIFTAP.  These may be used to set and get a

@i{tap function}.  The tap function will be called for every

Ethernet packet received by the interface.

These are called like other interface ioctls, such as SIOCSIFADDR.

When setting the tap function with SIOCSIFTAP, set the ifr_tap field

of the ifreq struct to the tap function.  When retrieving the tap

function with SIOCGIFTAP, the current tap function will be returned in

the ifr_tap field.  To stop tapping packets, call SIOCSIFTAP with a

ifr_tap field of 0.

The tap function is called like this:

@example

int tap (struct ifnet *, struct ether_header *, struct mbuf *)

@end example

The tap function should return 1 if the packet was fully handled, in

which case the caller will simply discard the mbuf.  The tap function

should return 0 if the packet should be passed up to the higher

networking layers.

The tap function is called with the network semaphore locked.  It must

not make any calls on the application levels of the networking level

itself.  It is safe to call other non-networking RTEMS functions.

@subsection Socket Options

RTEMS adds two new @code{SOL_SOCKET} level options for @code{setsockopt} and

@code{getsockopt}: @code{SO_SNDWAKEUP} and @code{SO_RCVWAKEUP}.  For both, the

option value should point to a sockwakeup structure.  The sockwakeup

structure has the following fields:

@example

@group

  void    (*sw_pfn) (struct socket *, caddr_t);

  caddr_t sw_arg;

@end group

@end example

These options are used to set a function to be called when there is

data available from the socket (@code{SO_RCVWAKEUP}) and when there is space

available to accept data written to the socket (@code{SO_SNDWAKEUP}).

If @code{setsockopt} is called with the @code{SO_RCVWAKEUP} option, and the

@code{sw_pfn} field is not zero, then when there is data

available to be read from

the socket, the function pointed to by the @code{sw_pfn} field will be

called.  A pointer to the socket structure will be passed as the first

argument to the function.  The @code{sw_arg} field set by the

@code{SO_RCVWAKEUP} call will be passed as the second argument to the function.

If @code{setsockopt} is called with the @code{SO_SNDWAKEUP}

function, and the @code{sw_pfn} field is not zero, then when

there is space available to accept data written to the socket,

the function pointed to by the @code{sw_pfn} field

will be called.  The arguments passed to the function will be as with

@code{SO_SNDWAKEUP}.

When the function is called, the network semaphore will be locked.

The function must be careful not to call any networking functions.  It

is OK to call an RTEMS function; for example, it is OK to send an

RTEMS event.

The purpose of these functions is to permit a more efficient

alternative to the select call when dealing with a large number of

sockets.

@subsection Time Synchronization Using NTP

@example

int rtems_bsdnet_synchronize_ntp (int interval, rtems_task_priority priority);

@end example

If the interval argument is 0 the routine synchronizes the RTEMS time-of-day

clock with the first NTP server in the rtems_bsdnet_ntpserve array and

returns.  The priority argument is ignored.

If the interval argument is greater than 0, the routine also starts an

RTEMS task at the specified priority and polls the NTP server every

`interval' seconds.  NOTE: This mode of operation has not yet been

implemented.

On successful synchronization of the RTEMS time-of-day clock the routine

returns 0.  If an error occurs a message is printed and the routine returns -1

with an error code in errno.

There is no timeout -- if there is no response from an NTP server the

routine will wait forever.