Messages in this thread | | | Date | Mon, 26 Sep 2022 12:17:16 +0200 | From | Maxime Ripard <> | Subject | Re: [PATCH v2 10/33] drm/modes: Add a function to generate analog display modes |
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Hi,
On Fri, Sep 23, 2022 at 11:05:48AM +0200, Thomas Zimmermann wrote: > > + /* 63.556us * 13.5MHz = 858 pixels */ > > I kind of get what the comment wants to tell me, but the units don't add up.
I'm not sure how it doesn't add up?
We have a frequency in Hz (equivalent to s^-1) and a duration in s, so the result ends up with no dimension, which is to be expected for a number of periods?
If you're talking about the comment itself, then NTSC mandates that a line is 63.556us long. If we're using a pixel clock at 13.5 MHz, it means that the period (== pixel) is ~74ns, so we get 63556 / 74 = 858 pixels / line.
> I think you want to end up with 858 pixels/line = > > 13,5 pixels/second / (60/2I frame/second * 525 lines/frame) > > I: interlaced > > Maybe just remove the short comments and document that in a more meaningful > place.
I guess this is where it's meaningful, we really want to hit that target. BT601 also mandates it.
Maxime [unhandled content-type:application/pgp-signature] | |