HDMI CEA Display Timings on i.mx6

[markwilczynski]

Hello,

I'm evaluating the i.mx6 for a media player project and need to know if the system can support the common CEA timings for 1080p video over HDMI connection.

I need support for the following display modes:

Refresh Rate, Horizontal Active Pixels, Front Porch, Sync Width, Back Porch, Total Pixels, Vertical Active Pixels, Front Porch, Sync Width, Back Porch, Total Pixels, Pixel Clock

23.976Hz, 1920, 638, 44, 148, 2750, 1080, 4, 5, 36, 1125,  74.2500 / 1.001 (= 74.175824175824175824175824175824)

24.000Hz, 1920, 638, 44, 148, 2750, 1080, 4, 5, 36, 1125,  74.2500

25.000Hz, 1920, 528, 44, 148, 2640, 1080, 4, 5, 36, 1125,  74.2500

50.000Hz, 1920, 528, 44, 148, 2640, 1080, 4, 5, 36, 1125, 148.5000

59.940Hz, 1920,  88, 44, 148, 2200, 1080, 4, 5, 36, 1125, 148.5000 / 1.001 (= 148.35164835164835164835164835165)

60.000Hz, 1920,  88, 44, 148, 2200, 1080, 4, 5, 36, 1125, 148.5000

Looking through the available reference manuals and source code for the i.mx6, it appears that all the existing video mode presets are based on a 74.25 or 148.5 Mhz pixel clock.  Does the hardware support a 74.1758/148.3516... clock necessary for the 59.940Hz display modes?

What changes would need to be made to allow the u-boot bootarg parameters to accept the above modes such as:

video=mxcfb0:dev=hdmi,1920x1080M@59,if=RGB24

Thank you.

[markwilczynski]

Since there's no reply, I'm going to assume the i.mx6 does not actually support all CEA-861-D HDMI timings as defined by the official specifications available here:

http://blogimg.chinaunix.net/blog/upfile2/090903185737.pdf

I guess this was implied by section "33.2.6.1 CTS Calculation" of the "i.MX 6Dual/6Quad Applications Processor Reference Manual" where it states TMDS clocks divided or multiplied by 1,001 coefficients are not supported.  For example, this means we can't support 1920x1080@59.940p with 48Khz audio rate by setting N=5824 and CTS=140625 as required by the HDMI specifications (see table 7-3 of HDMI 1.4 spec).

Thanks.

[daiane_angolini]

As I could remember you're right. There is some clocks/1.001 that are not supported. At least for video.

As I could remember @29 was not possible, we got @28.9... And it was caused by clock tree (but I don't remember how)

but, it's what I have in my head right now. Do you still need this information? I could search around for some additional info...

[markwilczynski]

Thank you for confirming my findings Daiane.  Looks like the i.mx6 will not work for my application.

I'm building a product similar to the i.mx6 based Ceton Echo video extender/streamer.  Since it's intended for the U.S.A. market, it would need to be able to display 59.940 field rate (for interlaced content) and 59.940 frame rate for progressive content.  If we played such content at 60.0, we would need to repeat a video frame every 16.666 seconds to keep the audio and video in sync.  I find that repeating frames like this is too visually distracting.

Please let me know if you find any alternative solutions to this problem or if there's some undocumented method to setup the HDMI clock/pll so that it can output modes requiring 148.352 or 74.176 Mhz pixel clock as defined in the HDMI 1.4 specs.

Thanks.

[daiane_angolini]

I know there is an on going work to improve this. How it's an on-going work, I cannot detail it to you.

I would suggest you to enter a SR asking for it, or wait for some next release.

[rabeeh]

Hi,

I was wondering if there is an update about this issue (i.e. generating 23.976 refresh rate by generating a pixel clock of 74.2500 / 1.001).