[RTnet-developers] [RFT] RT-safe TCP support for RTnet

[Jan K. <jan...@si...>]

"TCP/IP is not supported, because it is not real-time, and there is
no clear way to force it to be real-time.  If you don't believe me, feel
free to try implementing TCP/IP yourself.  If necessary, an unlimited
quantity of you-can't-do-that hubris can be provided as encouragement."

[David Schleef, developer of the original RTnet, about 10 years ago,
http://www.rtnet.org/download/original-rtnet-0.9.1.tgz]

We are not claiming to have proven him completely wrong, but - as always
- nothing is pure black or white. :)


We are happy to announce the availability of basic but functional TCP
support for RTnet! Check out latest git, switch on
CONFIG_RTNET_RTIPV4_TCP, and maybe run the included examples.

Just please do not expect that everything is as "shiny" as with
full-blown TCP stacks. The primary use case are TCP clients under RT
constraints, connecting to existing devices that only talk this
language. We do support the server scenario nevertheless, but accept()
behaves a bit differently and some corner cases may not yet work perfectly.

Moreover, you have to tune your socket for sufficient packet buffers,
specifically as you need to keep a temporary copy of each transmitted
fragment around for the sake of retransmission on error. This is, BTW,
limited to 3 tries so that the application is able to handle the error
before its too late. Check out Documentation/README.tcp for more details.

Lots of credits go to Vladimir who did the hard work of developing this
complex beast from scratch. Thanks a lot!

And I know at least one person outside Siemens is already waiting to try
this out - so don't hesitate, we hope to hear your feedback.

Jan

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux