nanog mailing list archives
Re: Laptop with reverse VGA
From: Neil Harris <neil () tonal clara co uk>
Date: Tue, 21 Feb 2012 17:19:10 +0000
On 21/02/12 14:48, Jay Ashworth wrote:
----- Original Message -----From: "Jake Khuon"<khuon () neebu net> I think the form-factour is already there. I have a Motorola Atrix smartphone. It's available with a laptop-dock unit. This is essentially a USB hub and display. The display is connected by outputting from the phone's HDMI port. The rest of the input/output device (keyboard and trackpad) are seen as USB connected devices and interfaced via the phone's USB port (Atrix supports USB host mode). Essentially, this laptop dock is what people are talking about except for a generic host instead of for a phone. We would want to expose the HDMI input generically and probably with an additional VGA input. Of course there are also VGA-HDMI converters. Anyone wanna ring up Motorola to see if they're interesting in adapting the Atrix laptop-dock technology?As someone who's done video for 20 years, I can tell you, Jake: It ain't that easy. The interface on the Atrix is purpose-built, and it's almost certainly just a DVI/HDMI digital interface to a panel that expects that. What's necessary for a standalone KVM of the sort we're talking about is what the video people call a "genlock" circuit -- most machines that need this at all have analog VGA out, and you have to have a chip that can lock up to it, and extract the video from that analog signal cleanly. This is, to quote the Jargon file, decidedly non-trivial to do well. That's the reason why a single port unit, not on sale, is generally around $400. If it was DVI/HDMI *only*, it could be substantially cheaper, but I've never seen one that was. Cheers, - jra
High prices are more likely to do with the small market for such devices, than to do with the cost of the underlying technology.
It isn't so much genlock, as accurate pixel clock recovery, that's the hard thing.
It is indeed hard to do well, but fortunately the chipmakers have done all that for you. It's a common enough need (think flat panel monitors) that there are inexpensive single-chip solutions for it that not only do the A/D conversion, but handle the pixel clock recovery for you as well: see, for example, the Analog Devices AD9884A or ADV7441A.
Data sheets at http://www.analog.com/en/audiovideo-products/analoghdmidvi-interfaces/ad9884a/products/product.html and http://www.analog.com/en/analog-to-digital-converters/video-decoders/adv7441a/products/product.html respectively.
-- Neil
Current thread:
- Re: WW: Colo Vending Machine, (continued)
- Re: WW: Colo Vending Machine Joel jaeggli (Feb 20)
- Re: WW: Colo Vending Machine Jay Ashworth (Feb 20)
- Re: WW: Colo Vending Machine Mario Eirea (Feb 20)
- Laptop with reverse VGA Jussi Peltola (Feb 20)
- Re: Laptop with reverse VGA Faisal Imtiaz (Feb 20)
- Re: Laptop with reverse VGA Jon Lewis (Feb 20)
- RE: Laptop with reverse VGA Scott Berkman (Feb 20)
- RE: Laptop with reverse VGA Mario Eirea (Feb 20)
- Re: Laptop with reverse VGA Jake Khuon (Feb 20)
- Re: Laptop with reverse VGA Jay Ashworth (Feb 21)
- Re: Laptop with reverse VGA Neil Harris (Feb 21)
- Re: Laptop with reverse VGA Jay Ashworth (Feb 21)
- Re: Laptop with reverse VGA Jussi Peltola (Feb 21)
- Re: WW: Colo Vending Machine Jimmy Hess (Feb 21)
- Re: WW: Colo Vending Machine Joe Greco (Feb 20)
- Re: WW: Colo Vending Machine Jon Lewis (Feb 20)
- Re: WW: Colo Vending Machine Jussi Peltola (Feb 20)
- Re: WW: Colo Vending Machine Jay Ashworth (Feb 20)
- Re: WW: Colo Vending Machine Robert Bonomi (Feb 20)
- Re: WW: Colo Vending Machine Owen DeLong (Feb 21)
- Re: WW: Colo Vending Machine Dale Shaw (Feb 29)