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I want to connect my Raspberry Pi (Model B rev2) with XBMC (see raspbmc.org) to an old steam powered CRT TV that has a SCART input. Hooking up the Raspberry Pi to the TV via a single SCART cable is not the problem, since there are dedicated pins for the composite video and stereo audio signals for that.

However, the challenge is to get AV.link to work over SCART as well. I want this to work, so I can use my TV remote to control XBMC's menus on the Raspberry Pi.

Is there a way to implement an AV.link device using a Raspberry Pi? Maybe with a USB peripheral, or even using the GPIO port? If that doesn't exist yet, could the GPIO port be used to make that happen at all (in theory)?

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From the AV.link link we see

Each bit transferred begins with a falling edge. The duration of the low period determines the value. Data bits are 2.4±0.35 ms long, with 1 bits having a low period of 0.6±0.2 ms, and 0 bits having a low period of 1.5±0.2 ms. Receivers observe the data line at 1.05±0.2 ms after the falling edge to determine the bit's value. Every message begins with a special start bit, 4.5±0.2 ms long, with a low period of 3.7±0.2 ms.

Because this is timing sensitive, it will be difficult to do from the Raspberry Pi GPIO. You'd at least have to turn off interrupts while you are trying to to this in software.

It may be possible to hack something with the PWM (you'd still need to update the PWM very often) and/or the SPI (use this as a way to stream bits - keep the buffers full).

Probably best is if you can find someone/thing who does it already. Otherwise consider using a micro to interface between the Raspberry Pi and the SCART.

There were serial (UART) dongles for HDMI-CEC before the USB ones, so maybe you can find a serial one for AV.link.

  • I was afraid that doing it purely in software would be tough. A dedicated peripheral that knows the AV.link protocol would be nice, but so far my searches of the internet make it seem like nobody ever made one. And I'm just a silly old software engineer incapable of building something like that. – derabbink Dec 15 '13 at 20:50

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