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TMS320DM8148: How to switch off sync on the CVBS output?

Part Number: TMS320DM8148

Hi,

has anybody an idea how to switch off sending sync signals on the CVBS (TV/SD) output? We're using S-Video in PAL or NTSC format out off an DM8148 HDVPSS.

I found the video processor register documentation in the DM38x DaVinci™ Digital Media Processor High-Definition Video Processing Subsystem (HDVPSS) User's Guide (spruhi7a.pdf) and the corresponding sources and currently I am setting the register SD_VENC_cvbs0, namely the bits 27-16 and 11-0 to 0, but still the monitor shows a (albeit distorted and totally unstable) picture.

Is there another way to suppress sync on the TV out? When I just switch off the driver, the monitor still syncs on a signal. The reasoning behind this is that some displays are switching off the backlight too when they can't sync.

regards,

Uli

  • Hi,

    Which software release are you using?

    Regards,

    Anuj

    Pathpartner Technology Pvt Ltd

  • Hi,

    the code I've added is on top of TI81xx-HDVPSS-01.00.01.37. But I think that this has no impact, as when I read out the register after setting them, the values are exactly as they should be. However, I found out that the behavior depends on the monitor! Some are just reporting "no sync" as expected, some are stubbornly trying to sync on something...

    So, is there another register on the HDVPSS which I can modify to reduce the chances of monitors still syncing on the signal somehow, or am I just out of luck and I need to switch off the driver, too?

    Regards,
    Uli
  • Hi Ulrich,

    Do you want to switch off (suppress) the below signals/pins?

    VOUT[0]_HSYNC/AC11
    VOUT[0]_VSYNC/AB13

    VOUT[1]_HSYNC/AC24
    VOUT[1]_VSYNC/AA23

    Regards,
    Pavel
  • Hi Pavel,

    these are the physical pins from the ti814x, right? As the software I am modifying is the HDVPSS driver, do I have direct access to disable output on these pins directly? I just want to switch off hsync and vsync temporarily, not via pin muxing completely....
    Or is there something I am not aware of and the output on these pins is not under control of the HDVPSS part of the ti814x? You sincerely have confused me...

    Regards,
    Uli
  • Ulrich Teichert said:
    these are the physical pins from the ti814x, right?

    Yes

    Ulrich Teichert said:
    As the software I am modifying is the HDVPSS driver, do I have direct access to disable output on these pins directly?

    Yes you can access these pins from linux kernel (driver), but not from user space

    Ulrich Teichert said:
    You sincerely have confused me...

    Why? I didn't get you any directions so far, I just asked you one question in order to understand your issue. Why you get so much confused by a simple question?

    Regards,
    Pavel

  • Hi Pavel,

    I am easy to confuse when it comes to hardware, being mainly a software guy :-) I appreciate your effort to find out what my problem is, really.

    Knowing that the signals of the TV out (CVBS) are under control of the HDVPSS, and modifying it's registers got me somewhere, I thought that these registers *exclusively* define what's going on on the TV out. But your question suggests to me that this is wrong and other parts of the ti814x are having physical access to these pins as well, so that I may be looking only at a small part of the generating of the video out signals. I hope that this is not the case, but it confused me...

    But you probably just wanted to suggest a more radical solution to my problem by switching off the output on these pins, yes?

    Regards,
    Uli
  • Ulrich,

    One solution I can think of is to cut off (gate) the input clock of the HDVPSS subsystem. This clock is coming from Video PLL. Once this clock is gated, I expect that the signals on the sync lines will stop.

    Another approach might be to change the pinmux from vsync to reset value (MUXMODE[7:0] = 0)

    Regards,
    Pavel
  • Hi Pavel,

    thanks for your suggestions, I've played with the clock settings before, but not to a point where I was satisfied. I'll try both and will report back, but that will take a while,

    regards,
    Uli
  • Uli,

    You can also try with disable the VENC used from user spacer with sysfs entries:

    Enable/Disable the VENC
    # echo 0/1 > /sys/devices/platform/vpss/display0/enabled
    # echo 0/1 > /sys/devices/platform/vpss/display1/enabled

    You can also try with changing the clock source with invalid one:

    echo dclk/dclkdiv2/dclkdiff > /sys/devices/platform/vpss/display0/clksrc
    echo aclk/aclkdiv2/aclkdiff > /sys/devices/platform/vpss/display1/clksrc

    See the below wiki page for more info:

    processors.wiki.ti.com/.../TI81XX_PSP_VPSS_Video_Driver_User_Guide

    Regards,
    Pavel