ltc

Wingless,
Again, there is no CAN Infotainment bus in the Cayenne. The closest CAN gets to infotainment is the CAN-MOST Gateway back in the instrument panel; thus your wiper control module has NOTHING to do with the MOST infotainment bus.

There is no US currently defined function for the A/V button.

Based on Kevin's initial description, it does not appear as though NAV-TV has enabled this button, as they require an external video switch. It sounds as though they have gone into the PCM and worked backwards from the LCD display and found a convenient (analog) point to switch video input sources.

There is a risk in taking video and audio from 2 asynchronous sources (remember that MOST is synchronous by design). There is a very low threshold in timing between seeing people's lips move and hearing the sounds (10's of milliseconds) that people can perceive. By taking an analog source (in this case video) and digital (audio) and inserting latency in the digital path (say due to error correction, DSP processing ,etc), you run the risk of crossing this threshold. This is why most 'wireless' speakers are analog (no latency issues) when used in home theatre systems.
As currently architected and as far as I am aware, none of the Porsches are able to accept 2 asynchronous streams (video and MOST audio).

As far as seeing A/V delivered from the manufacturer, Porsche will most likely wait until PCM3 and Audi will most likely add this to the A8L (already a MOST vehicle) in Europe. These would both be Becker headunits, as the only other company I am aware of making a MOST headunit is Panasonic and that is used exclusively in Japanese S class.

You might try posting additional questions regarding the Becker A/V functionality over on the Becker board.

wingless

According to readily available documents, such as the manual, “Porsche Service Information Technik”, there are four CAN busses on the Cayenne. These are: the CAN Infotainment bus; the CAN Drive bus; the CAN Comfort bus and the CAN Internal bus. This may be seen on pages 9.8 / 2004 and 9.9 / 2004 of that manual. The CAN Infotainment bus links the systems defined in my prior post. The Drive bus, the Comfort bus and the Internal bus each link some of the remaining vehicle systems. It appears that Porsche grouped unrelated systems, such as the PCM and the wipers together, to distribute loading and traffic across the four data busses.

https://rennlist.com/forums/showthre...hreadid=112032

Other than the two posts, by ltc, in this topic, I have been unable to locate any reference to a MOST Infotainment bus. All documentation I have found refers to the fiber optical bus as a MOST bus. It may be that internal, proprietary, documents define the MOST Infotainment bus designation, but I don't have access to that information.

It may be that the AV pushbutton functionality is limited to responding to actuation by displaying the message: "AV not available". It may be that the PCM hardware and software is currently structured to report to the Porsche System Tester the AV status as: disabled, without permitting changing the status to: enabled. It may be that the PCM rear panel video TV input connector is added to the PCM to provide a handle to grab onto, without any internal supporting hardware or software. I don't know.

It may also be, as I've previously stated, that it may be possible to toggle the video status to enabled and then input video through that rear panel connector.

If that is the case, then the audio also needs to go through the PCM, which I why I think NAV-TV reroutes the audio, from selecting MOST as the source to selecting the FM as the source.

Yes, there will be a delay between the video and the audio, but there are two reasons why I think this would be small. One is cost. The PCM needs to have received and processed enough audio data to provide a real time output. The PCM system would have been analyzed to determine the worst case conditions, to determine the required size for the memory buffer, to ensure that the PCM is not waiting for packets of music data. Then, that buffer size would then be increased to create a safety margin. It would not make sense to then artificially increase the buffer size, again, which would result in more sound data sitting in memory, a larger delay, between audio and video, not to mention an unnecessary cost hit, for the extra memory, for every single PCM produced.

The other reason I think the latency would be small is that Porsche currently offers a MOST telephone, for Europe only. This system sends full duplex voice data, through MOST. It seems reasonable to expect that this system will perform equivalent to other hands-free telephones and not have a noticeable delay, such as when having watched communications with Apollo astronauts on the moon.

The existence of a small delay because video is sent analog and audio is sent MOST, may still be acceptable. This is a car A/V system, with a 6.5" LCD display, not a home theater system with a 50" screen. The requirement for these two applications is significantly different.

It would be very interesting to see an actual system modified by NAV-TV. It would be very interesting to see if that system provides video, without audio, when playing a movie, but not having flipped the switch. It would be very interesting to see if the PCM, modified by NAV-TV, has the AV pushbutton enabled, to support, or refute, my theories.

This is the link to the Strosek A/V system, described in the post by eyeglaskid.
http://www.strosek.de/prog08/prog05d.htm

wingless

The people at NAV-TV have announced that they have implemented this change: http://forums1.roadfly.org/porsche/f...4951898-1.html

Periokid

That seems great. I want to add a rear camera and that would work for me!!

mm

Excellent Post!