Hi Maxime, On Thu, Aug 18, 2022 at 5:46 PM Maxime Ripard <maxime@xxxxxxxxxx> wrote: > On Thu, Aug 18, 2022 at 05:34:30PM +0200, Geert Uytterhoeven wrote: > > On Thu, Aug 18, 2022 at 3:42 PM Maxime Ripard <maxime@xxxxxxxxxx> wrote: > > > I started adding more sanity checks to my code, and I just realised I > > > don't seem to be able to reach 720 pixels over a single line though. If > > > I understood it properly, and according to [1] the active part of a line > > > is supposed to be 51.95us, and the blanking period taking 12.05us. [2] > > > in the timing section has pretty much the same numbers, so it looks > > > sane. > > > > > > At 13.5Mhz, a pixel is going to take roughly 74ns, and 51950 / 74 = 702 > > > pixels > > > > > > It seems we can go push it to 52350 ns, but that still gives us only 706 > > > pixels. > > > > > > Similarly, if I just choose to ignore that limit and just take the > > > active time I need, 720 * 74 = 53280ns > > > > > > That leaves us 10720ns for the blanking period, and that's not enough to > > > fit even the minimum of the front porch, hsync and back porch (1.55 + > > > 4.5 + 5.5 = 11.55us). > > > > > > Are those constraints merely recommendations, or am I missing something? > > > > You are missing that the parts near the borders of the full image are > > part of the overscan range, and may or may not be visible, depending > > on your actual display. > > The full 768x576 image size from BT.656 is not visible on a typical PAL display, > > and is more of an "absolute maximum rating", guaranteed to cover more > > than analog PAL. > > So the overscan range is not part of the active area, unlike what HDMI > is doing for example? Indeed. DVI-D and HDMI etc. are pure digital (let's ignore they are a digitized variant of old analog VGA ;-), hence there is a one-to-one match between pixels in the image and pixels on the screen (ignoring scaling). But even when using an analog VGA input on a modern digital display, you have controls to e.g. move the image. > Is there some minimal timings available somewhere to fit those absolute > maximum ratings? I guess they can be found on the Internet... Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds