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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  networktasks.t,v 1.8 2002/01/17 21:47:45 joel Exp

@c

@chapter Network Task Structure and Data Flow

A schematic diagram of the tasks and message @b{mbuf} queues in a

simple RTEMS networking application is shown in the following

figure:

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NO ASCII VERSION OF THE TASKING FIGURE IS AVAILABLE

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@image{networkflow,5in,6in}

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     ALT="Network Task Structure and Data Flow">

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The transmit task  for each network interface is normally blocked waiting

for a packet to arrive in the transmit queue.  Once a packet arrives, the

transmit task may block waiting for an event from the transmit interrupt

handler.  The transmit interrupt handler sends an RTEMS event to the transmit

task to indicate that transmit hardware resources have become available.

The receive task for each network interface is normally blocked waiting

for an event from the receive interrupt handler.  When this event is received

the receive task reads the packet and forwards it to the network stack

for subsequent processing by the network task.

The network task processes incoming packets and takes care of

timed operations such as handling TCP timeouts and

aging and removing routing table entries.

The `Network code' contains routines which may run in the context of

the user application tasks, the interface receive task or the network task.

A network semaphore ensures that

the data structures manipulated by the network code remain consistent.