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TMS320DM368: VPBE external clock oscillator range

alessandro piscozzo
Prodigy 90 points

Part Number: TMS320DM368

Hi,

we have an existing product (not new design) on which we're trying to add a new video feature.

We want to achieve 1080p - 60fps

We are driving the TMS320DM368's VPBE with and external clock of 74.25 MHz.

With the current settings of our PLL we achieve 30 fps.

To get to 60 we have two options:

1) change the PLL settings doubling the internal frequency (keeping the external oscillator at 74.25 MHz)

2) doubling the external frequency and bringing that at 148.5 MHz

I don't think that the option 2) is viable.

The app note http://www.ti.com.cn/cn/lit/ug/sprufg9c/sprufg9c.pdf at pag. 59 sets the range of the external clock to 75 MHz.

Am I correct?

Thanks,

Alessandro

  • 0
    TI__Guru**** 170625 points
    Hi Alessandro,

    Yes, option 2 is not possible. The max value you can get on EXTCLK pin is around 75MHz (13.33ns), as DM36x datasheet states:

    www.ti.com/.../tms320dm368.pdf
    Table 6-51. Timing Requirements for VPBE CLK Inputs

    I also doubt option 1 is possible, as DM36x datasheet clearly states that it support up to 1080p 30fps video:

    - Capable of 1080p 30fps H.264 video processing
    - Developers can now deliver crystal clear multi-format video at up to 1080p H.264 at 30fps (encode and closed-looped decode) in their digital video designs
    - The DM368 is capable of achieving HD video processing at 1080p 30fps H.264

    Regards,
    Pavel
  • 0 in reply to Pavel Botev
    Prodigy 90 points
    Hi Pavel, thanks for your answer. I see that the clock frequency cannot exceed 75 MHz. Thanks.

    Regarding the output format:

    actually I'm not interested in video playback at 60fps. I only need to generate a video signal.
    The bits 7:6 in the VMOD register in the VENC block include standard modes 720p and 1080i both of which have 60Hz field.... 1080p would be a "nonstandard mode" with the clock being manually specified.

    Is there anything wrong in my reasoning?

    Regards,
    Alessandro
  • 0 in reply to Pavel Botev
    Prodigy 90 points
    Hi Pavel, thanks for your answer. I see that the clock frequency cannot exceed 75 MHz. Thanks.

    Regarding the output format:

    actually I'm not interested in video playback at 60fps. I only need to generate a video signal.
    The bits 7:6 in the VMOD register in the VENC block include standard modes 720p and 1080i both of which have 60Hz field.... 1080p would be a "nonstandard mode" with the clock being manually specified.

    Is there anything wrong in my reasoning?

    Regards,
    Alessandro
  • 0 in reply to alessandro piscozzo
    TI__Guru**** 170625 points
    Alessandro,

    Yes, 1080i and 720p modes are supported, and the clock frequency needed for these modes is 74.25MHz

    www.ti.com.cn/.../sprufg9c.pdf

    1.1.2 Video Encoder (VENC) Features
    Master clock Input - 74.25MHz for 720p/1080i


    Regards,
    Pavel
  • 0 in reply to Pavel Botev
    Prodigy 90 points

    Hi Pavel, thanks for your answer.

    I know that 1080i and 720p are supported in video playback mode. The datasheet and the app note state that very clearly. Thanks for the tip about che clock frequency. Our external clock generator is 74.25 MHz.

    Actually my question was:

    Is it possible, to generate a video signal 1080p - 60fps varying SYSCLK6 (from PLLC1) or SYSCLK5 (from PLLC2)? We just need to generate the signal, without any closed loop processing.

    Is this theoretically possible in your view? I know it would be a "non-standard" video output mode and I know that there might be effects on the overall clocking tree system.
    We're talking about changing multiplier and divider of PLL's output in order to generate a frequency for the VENC which is as close as possible to 2x 74.25 MHz.

    Is there any physical limitation in doing that?

    Thanks and regards,
    Alessandro

  • 0 in reply to alessandro piscozzo
    TI__Guru**** 170625 points
    Alessandro,

    The Maximum Operating Frequency that VPBE module can operate is 74.25MHz, check below datasheet section:

    3.3.5 Processing, Video, EDMA and DDR EMIF Subsystems Maximum Operating Frequencies

    Regards,
    Pavel