Bridge IEEE 1394 FIREWIRE & IEEE 1284 LPT

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29 Mar 2010 02:27 - 29 Mar 2010 19:54 #2466 by sudrienet
Hello every body,
I am interested in EMC2 but from my point of view there is something problematic about LPT hardware. Today this is more and more difficult to have a LPT db25 connector on computer and on last laptop this finish no LPT at all.

For the desktop we can add a PCI card but there are some difficulties about compatibility with Linux this is not so simple. On new laptop generation only USB an FIREWIRE are available. This mean that one day (soon) the LPT port will disappear on all our home computer.
Of course this easy to had an LPT port true an USB converter but the problem with USB this latency and priority this why INRIA's guys who play with SCIOS SCILAB (www.scicos.org/scicosrtai.html ) or other RTAI stuff on USB always said "be careful we can not be sure that latencies are correct". Controlling a motor on a milling machine will be a bit problematic if when you directly drive the motor from computer we have some latencies incertitude . So Inria made only proof of concept with Usb and they said that they hope maybe one day the usb will be fully useable in RTAI .

So why not using FIREWIRE in order to drive motors !

From my point of view FIREWIRE :
-Is more perennial than actual lpt port for the future.
-On Linux there is a generic driver in order to use the firewire (I use it in order to link 2 computers and made some Ethernet on firewire with 2us latency).
-You can control more modules than LPT and this is easy to make a chain.
-You can be sure about latency.
-Connector and wire are more tiny compare to LPT shielded cables.
-This is not expensive.
-This bus have a big bandwidth.
-This use a differential signal less sensitive to interference.
-Length of the cables.
-FIREWIRE is full RTAI.

I have crawl the net in order to find this "holy Graal" but nothing ... the only clue I be able to find was that this is possible to connect an lpt parallel interfaces module to firewire 1394 serial with a bi-directional bridge "IEEE 1394 can interface with the higher layers of the new parallel port standard, IEEE 1284" english.cxem.net/comp/comp8.php or 209.85.129.132/search?q=cache:atxUv8Irq6...&hl=fr&ct=clnk&gl=fr


So I wonder if this possible to find a converter / bridge in order to connect an LPT PAP driver to the FIREWIRE bus ?

And if EMC2 will be able to control a motor with FIREWIRE ?

Thanks for your help.
Last edit: 29 Mar 2010 19:54 by alex_joni.

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31 Mar 2010 01:13 - 31 Mar 2010 01:17 #2484 by sudrienet
On the wiki 3.1. Ethernet wiki.linuxcnc.org/cgi-bin/emcinfo.pl?Emc2HardwareDesign#USB i found this

In principle, the RTAI realtime kernel has a network interface, rt-net. However, no one has ever submitted a driver that uses rt-net. It is not clear whether rt-net as written will work with HALs timing model.


On link www.rtfirewire.org/ RTNET over ethernet on FIREWIRE there is a very interesting white paper www.rtfirewire.org/paper.pdf
At page 7 of this pdf we learn that :
-The firewire need more layer RTnet / Eth1394 / RT-firewire kernel / Firewire driver than the Rtnet on Ethernet.
-The project seems to be in alpha they thinking about using 1394AP (1394 Au-
tomation Protocol) or CanOpen.

In the same pdf they made a test with RTNET on firewire 400mb VS Rtnet on ETHERNET 100mb they have the same results (Figure 14) this mean that the actual layer are not optimized on firewire and the layers Eth1394/RT-firewire kernel have a big impact on the benchmark.

Page 7/8 They present a very interesting study case but actually is not suitable for end user.

For information this website is dedicated to the rtfirewire developer.berlios.de/projects/rtfirewire/

If you go on www.rtnet.org/ there is RTNET over ethernet wire on a dedicated nic :

The figure above shows a typical configuration of an RTnet real-time network. To achieve deterministic behaviour, a dedicated network segment is required. Non-real-time traffic will be tunneled through this segment. One of the three real-time stations is configured as a gateway to arbitrary non-real-time networks.


Something interesting with Ethernet is this is not very expensive and you can find some microcontroled board (arm) with Ethernet port and every thing seems to be compliant with Linux RTAI. www.friendlyarm.net/mini2440/mini2440_overview.pdf without the need of adding a firewire bridge and a connector to the board. In conclusion this mean that actually if you take a good Ethernet gigabyte NIC you can expect better time slope and latency than with actual rt-firewire project.

This is certainly most simple and less expensive for end users to deal with RTNET over Ethernet I will take a look and open a new topic !

If you found more information on rt-firewire please share it on this topic !

Thanks
Last edit: 31 Mar 2010 01:17 by sudrienet.

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