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About routing if there are parts of the SoC i am not going to use

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  • About routing if there are parts of the SoC i am not going to use

    At the moment i am doing my first board with linux. Although a simple or a basic one.

    I don't need HDMI, USB or SATA. I only need Ethernet.

    The SoC that i am going to use is an Allwinner A20.

    And I have the following question ?

    1.- Can i not to route the balls of the SoC for those targets ?

    I mean, can i leave the power balls of those parts ( HDMI ) as not connected ?

    Will the board work in a proper way if i don't use all those parts of the SoC ?

    What must i do about all the balls of the SoC that i am not going to use ?

    2.- By last, what do you think about this SoC ? I think the support of the manufacturer is very poor, however it has a very good community (Linux Sunxi) and you can find a lot of open source projects on internet

    Thank you very much in advance

  • #2
    Be careful with the interfaces, you never know what you might need. Normally it's not that more difficult to include a few of them instead of just one. For example a simple UART with an UART to USB converter could be super useful for console debugging. I don't have much experience with debugging/getting linux chips to boot/work, but from my experience with working with people who do that, I've established that it could be problematic many times. So think about different debug options and how would you deal with eventual problems.

    1. Many times you can leave different IO/signal pads not connected. However, sometimes it is recommended to pull those high/low either directly or through a resistor. This information should be provided in the datasheet/manual/design guide. With power pads is a similar story - sometimes you can just leave them floating but many times you still need to power them or connect them to ground. I am not sure what the consequences will be if you don't follow those guidelines, but I would rather follow them to be sure everything is fine - considering how risky the PCB design is in general.

    2. As the bare minimum, I would recommend to have very detailed datasheet/manual. Apart from that it's always good to have a decent support. I am not sure how good and developed this community is - especially with regards to the hardware side.


    • #3
      Thank you mariomaster. The problem is that there is not any guideline about it.


      • #4
        Definitely follow mairomaster's recommendations.

        I have not done any designs based on Allwinner, but I heard, the support and documentation is not the best. I normally try to avoid this kind of chip manufacturers (with poor support), but if price is very important for your project, you may not have many other options. Also, test the boards first as I am not sure about performance - that can be sometimes the hidden "cost" behind the low price (e.g. I checked "datasheet" and it says 32-bit memory bus which is half of throughput comparing to many other chips )


        • #5
          Thank you very much Robert