Comment # 28
on bug 76564
from jeroen
(In reply to comment #27) > (In reply to comment #26) > > (In reply to comment #25) > > > (In reply to comment #24) > > > > (In reply to comment #23) > > > > The problem is that the frequencys are exact enough so that the display > > > > device (Monitor/TV/Whatever) accepts them, but not 100% precise. > > > > > > > > E.g. for the 50Hz mode we wanted 148.5MHz pixel clock, but got 148.75Mhz > > > > instead. And for the 24Hz mode we wanted 74.2MHz but got 74.0625Mhz instead. > > > > > > > > So as Alex said somebody would need to dig into that and try to improve the > > > > numbers without toasting the hardware. > > > > > > So that would mean for example using fb=29.7 Ref=2 post=10? > > > > > > Or would that fry the hardware? > > > > That should work. You aren't likely to fry the hw. You just don't want to > > set a 400 Mhz clock as you monitor properly won't like it. The hard part is > > adjusting the algorithm to reliably calculate a good value for a wide range > > of clocks. > > I'm not sure if those values would work. A post divider of 10 might result > in a to high VCO and that could indeed damage the hardware (even if that's > rather unlikely). > > Essentially the target clock multiplied with the post divider must be in a > certain range. I think between pll->pll_out_max and pll->pll_out_min. > > I think the problem is that we don't try to choose a good value to match the > target frequency as close as possible in avivo_get_post_div, but just a > value that either matches the maximum or minimum VCO frequency. Perhaps before somebody is going to modify the algorithm, it is a good idea to verify that this is indeed the problem. If this is the problem why don't more people have these problems? If I know which values for fb,ref and post to use for 23.976fps I can hard code these In a patch and test if it indeed works. So which values are save to get a clock of 74.2MHz?
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