[PATCH 6/9] drm: bridge/dw_hdmi: adjust pixel clock values in N calculation
dianders at chromium.org
Sat Sep 5 12:44:51 PDT 2015
On Sat, Sep 5, 2015 at 7:01 AM, Russell King - ARM Linux
<linux at arm.linux.org.uk> wrote:
>> If you know the answer, just tell me. If you're talking about 74.25
>> vs. 32 kHz it is further evidence of what I'm saying. Note that
>> picking only one of the two listed CTS values again puts you in a
>> worse position for regenerating the proper audio clock then just using
>> the default N=4096.
> No it doesn't.
> 74.25MHz/1.001 * 4096 / (128 * 32000) = 74175 (rounded down)
> Now do the calcuation.
> (74.25MHz/1.001) / 74175 * 4096 = 4096045.511 => 32000.35556Hz
> => error of 0.001111%
> Now for the calcuation using the proscribed figures.
> (74.25MHz/1.001) / 210937 * 11648 = 4096009.709 => 32000.07585Hz
> => error of 0.000237%
Why would you round down??? Round to the closest.
(74250000 / 1.001 * 4096) / (128 * 32000.)
(74250000 / 1.001) / 74176 * 4096 / 128
That's actually the same error as yours: 0.000237%
You're right. Yours isn't worse, but it's also not any better.
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