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rtai-3.1-test3的源代码(Real-Time Application Interface )

Typed mailboxes and POSIX message queues modules for RTAI
=========================================================


------------------------ T Y P E D   M A I L B O X E S -------------------------

COPYRIGHT (C) 2001  G.M. Bertani ([e-mail]) 
                    (http://www.geocities.com/gmbertani)

This library is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2 of the License, or (at your
option) any later version.

This library is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
License for more details.

You should have received a copy of the GNU Lesser General Public License
along with this library; if not, write to the Free Softwre Foundation,
Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA.


Introduction
------------

Typed mailboxes (TBX) are an alternative to the default RTAI ones that offers:

1-Message broadcasting, that means send a message to ALL the tasks that are 
pending on the same TBX.

2-Urgent sending of messages: these messages are not enqueued, but inserted in
the head of the queue, bypassing all the other messages already present in TBX.

3-The PRIORITY/FIFO wakeup policy can be set at runtime when creating the TBX

Features (1) and (2) are achieved by adding a type field (1 byte) to every 
message inserted in a TBX, so when receiving it is possible to discriminate
normal, urgent and broadcast messages. The type field is silently removed by 
the receiving functions, so from the user point of view it is not visible.
Users must consider type fields only when specifying the TBX sizes.


System requirements
-------------------

RTAI-24.x.y (Linux 2.4.x) : http://www.rtai.org


Acknowledgements
----------------

Thanks to Paolo Mantegazza ([e-mail]) for his work in
changing this code from a simple upsched.c patch to an autonomous RTAI
module.


------------------- P O S I X   M E S S A G E   Q U E U E S --------------------

After discovering that Trevor's (Woolven) kernel space implementation of POSIX 
message queues was usable directly, almost unchanged, with RTAI, i.e. without 
the specific kernel POSIX support found within RTAI itself, it followed that
it had to work symmetrically in user space also.
Its structuring within RTAI appears similar to TBXes, i.e an extension of RTAI
intertask communication APIs, not born in the RTAI schedulers directly. So it
goes into the existing "tbx" directory, along with its (NEW)LXRT user space 
extension module.
So to use POSIX message queues everywhere you'll have just to care of insmoding
the related modules: rtai_pqueue.o and rtai_pqueue_lxrt.o found here, the 
related header file, rtai_pqueue.h, is found in directory "include". It is the
same for both kernel and user space applications.
It should be remarked that the rtai_pqueue.c file found here contains also 
timed version of send/receive, that are missing in its native parent found 
under the "/posix/src" directory. 
On the lucky side is that POSIX message queues are all natively based on the 
POSIX standard naming, thanks to the fact that RTAI core APIs had nothing 
similar to them yet.

Paolo Mantegazza.