Info needed about RCX IR protocol for my homebuilt tower

[peterjak]

I'm new to the forum having been led here by Yoda's advice "use the Google" and although I am not a Lego user I am an electronics engineer trying to help my dear wife with her science class. She has a problem in that the RCX USB IR tower only works on the old XP laptops but the old laptops can't connect to their wireless system. The newer laptops run a modified WIN7 with lots of security etc because students play with them (of course). The IT guy has been struggling for weeks to get the tower to work with the newer computers.

Being an engineer and seeing the problem I noticed that the Robolab software will work with serial coms ports as well. Knowing that USB serial coms drivers just work on any computer and OS I built up a small IR tower myself.

I am using a high-speed sensor so there are no problems there but the communication seems to be unreliable to say the least. I have checked the IR emitter and sensor and all the signals seem to be fine. Typically the problem appears somewhere during a firmware download or even after it completes the downloads the RCX just sounds a repeating low frequency one second tone and says it can't communicate. Done the basics, changed the batteries, eliminated interference, adjusted for optimal IR distance etc, and check the results on the scope.

Any clues?

Cheers,

Peter

Edited November 9, 2011 by peterjak

[jonwil]

I see no reason a driver for the USB IR tower couldn't be written that works on Windows 7 (I have a USB IR tower myself and would be interested in such a project)

Someone just needs to document the protocol for the USB IR tower (or get TLG to document it or release its source code)

[peterjak]

I see no reason a driver for the USB IR tower couldn't be written that works on Windows 7 (I have a USB IR tower myself and would be interested in such a project)

Someone just needs to document the protocol for the USB IR tower (or get TLG to document it or release its source code)

Windows drivers are a big pain in the butt and you have to worry about updates because something else has changed in Windows etc. Way easier just to use the USB serial drivers as they have been certified and they are updated by the manufacturer etc. I don't really need to know all about the protocol but maybe someone has some insight into it enough to throw a few clues my way. I made up the little USB serial tower in an afternoon and I don't really want to spend too much time on it (yeah, I'm lazy :) ).

[peterjak]

Not to be deterred I hooked up a logic/protocol analyzer to the IR coms transmit and receive. I found that when it tries to download the firmware that Robolab is not waiting long enough for a response from the RCX and while the response is in progress Robolab retries over the top of it. This is because it is over USB and the driver is receiving data byte by byte but it waits to deliver a packet rather than each byte as soon as it's received. I will see if I can tweak the settings for the USB serial driver and report back.

[DLuders]

Three-fourths of the way down this webpage about "The Lego RCX, Inside and Out", it has a paragraph about "Getting the RCX Software Running on New Machines". Here is an excerpt:

"The first way is to consider using Virtual Box. This allows you to forward USB ports and serial ports to a virtual machine, in which you can then run an older version of Windows and then run the original Mindstorms disks as is.

"You may get somewhere in using an older version of Quicktime to prevent errors in the default software. The exact version needed is 6.5.2 for the RIS 2.0 software (the most recent). This can be downloaded from Oldversion.com.

"Virtual Box is freely downloadable at Virtualbox.org. You will just need a version of Windows - I recommend 98 as there are no patches needed for it. Just make sure you use it only for Mindstorms and do not go on the net with it.

"In Windows 7, with the more expensive editions (which you can purchase through an Anytime upgrade), you get a version of Virtual PC, with an older version of Windows running in it, for just this kind of compatibility problem. However that is XP, and the compatibility patches that Lego were hosting have long since been removed.

"Unfortunately, Lego do not support the consumer RCX so much any more, so you may need to look for files on their education site.

LEGO Education - MINDSTORMS®: download. [NOTE: The old broken link updated here on Eurobricks]

"For a simpler route in terms of drivers and so on, you may find NQC and Bricx Command Centre easier, although programming them takes more work and patience."

[RohanBeckett]

I manage IT in schools, and this would have been my first thought:

Virtualize XP.

Lock it down, if need be - it probably doesn't need network/internet access, if it's just running RoboLab to talk to the tower.

Also.. interesting that 'old laptops can't talk to wireless'

Gov. schools here in Vic, Australia have all been recently upgraded to a new 'Enterprise Level' Wireless system (Cisco 5500 based, 802.1x, statewide centralized sign-on), and we still have plenty of old XP SP3 laptops working just fine..

RB

[peterjak]

I manage IT in schools, and this would have been my first thought:

Virtualize XP.

Lock it down, if need be - it probably doesn't need network/internet access, if it's just running RoboLab to talk to the tower.

Also.. interesting that 'old laptops can't talk to wireless'

Gov. schools here in Vic, Australia have all been recently upgraded to a new 'Enterprise Level' Wireless system (Cisco 5500 based, 802.1x, statewide centralized sign-on), and we still have plenty of old XP SP3 laptops working just fine..

RB

I have no trouble using VirtualBox as I use it all the time on my Linux systems but the impression I get is that they don't want to have to install and maintain it for hundreds of laptops. Also I just shrug my shoulders at the many things that they can't do in schools here in Queensland. They are just the sort of people that would and do still purchase tape drives for backup because they are "tried and proven"! My wife tells me they were boasting the other day that they were upgrading the school server for ONLY $20,000 and that it would have a massive 4TB!!!!!!!!!!!!!!!!!!!!!!!!! (exclamations are my "whoop-di-do"). I have 10TB or more just here at home (yawn).

Anyway I decided that there is a fundamental problem with timeouts in Robolab because of USB latencies so I have scrapped trying to do anything and they can sort it out.

Edited November 9, 2011 by peterjak