On Mon, May 22, 2017 at 07:55:56PM +0200, Jernej Škrabec wrote: > Hi, > > Dne sobota, 20. maj 2017 ob 03:37:53 CEST je Chen-Yu Tsai napisal(a): > > On Sat, May 20, 2017 at 2:23 AM, Jernej Škrabec <jernej.skrabec@xxxxxxxx> > wrote: > > > Hi, > > > > > > Dne petek, 19. maj 2017 ob 20:08:18 CEST je Icenowy Zheng napisal(a): > > >> 于 2017年5月20日 GMT+08:00 上午2:03:30, Maxime Ripard <maxime.ripard@free- > > > > > > electrons.com> 写到: > > >> >On Thu, May 18, 2017 at 12:43:50AM +0800, Icenowy Zheng wrote: > > >> >> Allwinner H3 features a TV encoder similar to the one in earlier > > >> > > > >> >SoCs, > > >> > > > >> >> but with some different points about clocks: > > >> >> - It has a mod clock and a bus clock. > > >> >> - The mod clock must be at a fixed rate to generate signal. > > >> > > > >> >Why? > > >> > > >> It's experiment result by Jernej. > > >> > > >> The clock rates in BSP kernel is also specially designed > > >> (PLL_DE at 432MHz) in order to be able to feed the TVE. > > > > > > My experiments and search through BSP code showed that TVE seems to have > > > additional fixed predivider 8. So if you want to generate 27 MHz clock, > > > unit has to be feed with 216 MHz. > > > > > > TVE has only one PLL source PLL_DE. And since 216 MHz is a bit low for > > > DE2, > > > BSP defaults to 432 MHz for PLL_DE and use divider 2 to generate 216 MHz. > > > This clock is then divided by 8 internaly to get final 27 MHz. > > > > > > Please note that I don't have any hard evidence to support that, only > > > experimental data. However, only that explanation make sense to me. > > > > > > BTW, BSP H3/H5 TV driver supports only PAL and NTSC which both use 27 MHz > > > base clock. Further experiments are needed to check if there is any > > > possibility to have other resolutions by manipulating clocks and give > > > other proper settings. I plan to do that, but not in very near future. > > > > You only have composite video output, and those are the only 2 standard > > resolutions that make any sense. > > Right, other resolutions are for VGA. > > Anyway, I did some more digging in A10 and R40 datasheets. I think that H3 TVE > unit is something in between. R40 TVE has a setting to select "up sample". That might be just another translation of oversampling :) I didn't know it could be applied to composite signals though, but I guess this is just another analog signal after all. > Possible settings are 27 MHz, 54 MHz, 108 MHz and 216 MHz. BSP driver on R40 > has this setting enabled only for PAL and NTSC and it is always 216 MHz. I > think that H3 may have this hardwired to 216 MHz and this would be the reason > why 216 MHz is needed. > > Has anyone else any better explanation? That's already a pretty good one. Either way, wether this is upsampling, oversampling or just a pre-divider, this can and should be dealt with in the mode_set callback, and not in the probe. Thanks! Maxime -- Maxime Ripard, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com
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