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SDVO spread spectrum settings of DVI

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Marcin Szewczyk's picture
Marcin Szewczyk

Jul 09, 2015 - 05:09am

  • I'm working on a software upgrade for a small embedded system (with Intel 945GM) that uses an SDVO to DVI chip to drive 1 monitor (DVI-D). It has small problems with EMI tests, where the device emits a tiny bit too much. We found source of the problem being DVI signal getting a bit out. On old setup running WindowsXP there was Intel Embedded Graphics Driver and utilities that could set up spread spectrum on DVI and mitigate the problem. We are switching to linux (Kernel 3.10 and 3.18) and cannot control the DVI spread spectrum. All data sheets for SDVO chips only say that control of spread spectrum registers is done through Intel's SDVO configurtion channel, but its datasheet is nowhere to be found. I've peeked into the i945 linux driver and it seems it is setting up the SDVO chip, but there is no reference to spread spectrum in it. Is there any way to set it up and I've missed it? And I've found settings for spread spectrum on eDP/LDVS/DP, but they do not apply to DVI over SDVO.


    The same problem goes for Ivy Bridge i3-3xxx that we can run in the same setup.


    Jul 09, 2015 - 05:09am