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Minimum DDR requirements for DM814x

Kevin Coombs
Prodigy 120 points

Hi,

I was wondering if there is a minimum memory requirement (or method to calculate it for a given application) for the DM8148.  Specifically, I am hoping to understand if I can turn one of the EMIFs completely off as a way to save power.

Thanks,

Kevin

 

  • 0
    TI__Genius 15310 points

    Kevin,

    For the available bandwidth you can use the following...

    Absolute max available bandwidth = bus width * clock * 2, so for a 16 bit bus (2 bytes) running with a 400MHz clock you can get 2 * 400,000 * 2 bytes per second throughput = 1.6GBytes/s.

    Now, in reality you will achieve between 60% & 70% of the max available bandwidth.

     

    For system requirements, this is a much more difficult question to answer, but there are some solid numbers you can use to help get in the right ballpark.

    Examples are...

    Display. If you have a display of 1080p60 with a 32 bit frame buffer then you need 1920x1080x60x4 bytes per second just to display an image. (474MBytes/second)

    If you have a CODEC running, generating video at 1080p30 then the CODEC will have 2 components to its requirements. 1) stream processing (these memory requirements should be in the CODEC datasheet) and 2) outputting the final image to memory. In this example it would be 1920x1080x30x2 for a YUV422 video output = about 118MBytes/second.

    If you are capturing video from the capture port then writing a 720p image to memory in RGB format would require 1280x720x60x4 = 211MBytes/second

    Encoding this and sending over Ethernet would need 211MBytes (for the CODEC read) plus the CODEC overhead (from the CODEC datasheet) plus the final Ethernet output + overhead.

    These are just examples of the things to consider when estimating the bandwidth requirements.

    You can use only 1 EMIF and leave other off if that's all you need.

    Regards,

    Viet