An other CPU discussion. Rockchip RK3399 sounds good

Discussion in 'General Discussions' started by Askarus, Jun 7, 2018.

  1. hns

    hns Very Active Member

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    Thickness should be <1.5mm (incl. solder balls and some reserve etc.) or the board risks to be pulled by bending forces out of the B2B connectors.

    Available area depends on what else is needed around the SoC chip.
    There is also a limitation by one of the magnetic nub sensors on the mainboard so it is kind of a puzzle game.

    Roughly we have for the OMAP5 board:
    * 20x20mm for OMAP5 plus some circuits around (oscillator)
    * 40x15mm for RAM chips
    * 15x13mm for eMMC
    * 16x15mm for Palmas power controller plus inductors and capacitors
    * 12x12mm for twl6040 audio codec
    There is also some random space which can be used for glue logic.

    Max. current draw: less than ca. 2A @ 3.7V (battery voltage). Peak current can be higher (ca. 3A from battery), but then the system is discharged faster than it can be charged.

    Thermal: not too hot :)

    Another important factor is the number of available interfaces - here is some minimum:
    * 3xSDIO (plus something internal for eMMC)
    * 2xUART
    * 4xI2C
    * 1xMIPI
    * 1xHDMI
    * 3xUSB2 (the OMAP5 boards has an on-board 3-port hub for that purpose)
    * 1xUSB3-OTG
    * 1xSATA or USB3 (then 2xUSB2 is sufficient)
    * Audio: 2x Handsfree speaker, Microphone, Line/Headset in/out, 1x vibramotor
    * ~30-40 GPIOs

    Also important: 1.8V I/O levels (unless defined otherwise by standard, e.g. SDIO, MIPI, HDMI, USB, SATA).
    If a SoC does not provide them all, it must have some expanders on the board.

    I did an evaluation ca. 2 years ago and a Z8550 would almost fit (except the power controller and the audio subsystem), but it is an Atom...
     
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  2. Askarus

    Askarus Hardcore Member

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    @hns
    I have attached an older Datasheet.
    The recent one I've seen some days ago is either taken down or I can't find it any more.

    However, the Requirements should be fulfilled.

    The only Issue might be the size. I could not find anything so far.
    I hope there is a way to make it fit.
     

    Attached Files:

  3. levi

    levi Still fresh, damnit!

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    :D

    It seems they are using their own hand-rolled license there, which is unusual. They're using it there and in the license for their mali binary implementation.
     
  4. Askarus

    Askarus Hardcore Member

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  5. EvilDragon

    EvilDragon Administrator Staff Member

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    Well, it's between 1.41 and 1.61 for the Rockchip, so tolerances are a hit and miss.
    Also, it would mean that the small heatpipe (0.2mm) wouldn't fit anymore.

    Sent from my Moto Z using Tapatalk
     
  6. Kuro

    Kuro Still Fresh

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    The size is on page 28 and acording to it, the thickness is 1.41 to 1.61mm with solder balls included.

    So it would be possible if we could get the minimum value, it seems unlikely but my knowledge about this stuff is almost none :(.

    Edit: Looks like I took to long to answer...
     
  7. Letalis Sonus

    Letalis Sonus Advanced Member

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    It's a fairly common practice for firmware blobs.
     
  8. levi

    levi Still fresh, damnit!

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    Looks about the same size as the iMX6 in my SBC which I measured for heatsink purposes as 20mmx20mm. That may have an internal clock though - the only non-passive looking components directly nearby are the DRAM and a buffered QFP surrounded by a small collection of passives. Certainly nothing that looks like a traditional crystal or resonator, but then I'm not 100% what a surface mount one of those looks like at all.
     
  9. Kuro

    Kuro Still Fresh

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    Just remembered but should it not be possible to get a thinner battery heat shield and slightly higher connectors for the cpu board to connect to the mainboard?

    How much space could be gained from such changes?
     
  10. Askarus

    Askarus Hardcore Member

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    If that would hinder us to use that processor then I don't see much benefit in using a modular design.
    If there are such strict limitations it will be even harder to get a new SoC.
     
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  11. vcoleiro1

    vcoleiro1 Hardcore Member

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    This video ED made shows the cooling system in the PYRA and the spaces available


     
  12. hns

    hns Very Active Member

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    Well, the thickness limitations aren't that strict. AFAIR there is some space between the PCB and the plastics case. And I think there are variants of the B2B connector (Hirose DF40C) giving 0.5mm more distance. So it might be possible to get a "thicker" board into the Pyra. Someone should check that before we assume that it does not work.
     
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  13. Askarus

    Askarus Hardcore Member

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    That sounds much better :)
    Let's be positive.
    You did a great job designing the board and making it modular.
    Let's not loose hope because of 0.2mm ;)
     
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  14. EvilDragon

    EvilDragon Administrator Staff Member

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    The space between the CPU board and the plastic is exactly 0.5mm and there is a 0.4mm aluminium plate cramped in there.

    So yeah, thinner CPU board and higher Hirose connectors would probably be the only real solution.
     
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  15. Askarus

    Askarus Hardcore Member

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    Do we really have to use Aluminium?
    Didn't we have much smaller tape for both, isolation and heat dissipation?
     
  16. hns

    hns Very Active Member

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    Well, if a new SoC doesn't produce that much heat, it could work without the aluminium plate. But that isn't easy to predict.
     
  17. levi

    levi Still fresh, damnit!

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    0.4mm is already entering tin foil thinnesses (it's about double the standard gauge apparently). You could use thinner things and back them with plastics and things, but the crosssection of the transmissive surface is proportional to the rate of heat transfer I assume, so anything that isn't doing that is a bad thing. As far as I recall, copper is generally a better conductor of heat, but it's also a lot more costly than aluminium. Actually, if cost weren't a concern you could probably use pure gold.
     
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  18. ImmaculateChimp

    ImmaculateChimp Member

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    how about using a graphite thermal sheet/pad?
    ...and protecting/isolating, electrically-conductive, sensitive areas (zap!:'()
     
    Last edited: Jun 10, 2018
  19. EvilDragon

    EvilDragon Administrator Staff Member

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    That tape is being used to move the heat out of the way from the SoC.
    It doesn't cool. You still need heatsinks and shield the battery.
     
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  20. rohezal

    rohezal Advanced Member

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    It it said, that an improved case, which is a few mm thinner, could maybe be produced in the future. Would it be possible to use one or two of this mm to make room for a future sock?
     

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