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Compact SOM?

shabaz

Hi, there are quite a few small MIPS based SOMs (about 40x30mm), that run to around 400MHz speed, and are very low cost.

 

I was curious what else was out there, with minimum BBB level performance, capable of running Linux (not uClinux), not necessarily

MIPS, could be Intel or ARM for example. Size should be ballpark 30x25mm.

 

For that type of performance and size, there are some products from LogicPD, but they are in the hundreds of pounds in a quantity of 1.

Intel Edison could be a very good choice when it arrives.

 

If such a thing doesn't exist at a price <<£100, what silicon and functionality would be worth considering, for an open source design? (Admittedly it

would be hard to go BGA, but it would need to be BGA at this level of integration, so let's assume this is fine, and up to 6-layer design).

I know it's not a lot of specs, some parameters will constrain size more than others.

 

Even if we can't physically implement it without BGA capability, I think it's still worth considering what a potential design could

look like, so we can compare with any platforms as they get released.

  • shabaz wrote:

    I was curious what else was out there, with minimum BBB level performance, capable of running Linux (not uClinux), not necessarily

    MIPS, could be Intel or ARM for example. Size should be ballpark 30x25mm.

    Maybe a bit bigger than what you're looking for, but how about http://www.mentorel.com/product/usomiq-am335x/  BBB level performance shouldn't be a problem image

     

    That 30x25mm footprint requirement is going to be problematic, the AM3359 is 15x15, i.MX6 20x20, so you're dangerously close to only being able to do SoC plus connector with no space left for ram, flash, uSD, PMIC, ethernet phy etc.

     

    I'll take a wild guess that some of those you've seen are expensive for two reasons. First is low volumes. Second is that they probably have high pcb layer counts, buried vias etc, in order to be able to increase the density by having two bgas essentially one on top of the other on opposite sides of the board.

    As a side issue, the high density connectors these tend to use will add a fair bit to the cost themselves.

     

    If you can sacrifice something in performance, then maybe something like https://www.olimex.com/Products/OLinuXino/iMX233/iMX233-OLinuXino-NANO/open-source-hardware

     

    Even if we can't physically implement it without BGA capability, I think it's still worth considering what a potential design could

    look like, so we can compare with any platforms as they get released.

    Within your space constraints you almost certainly need BGA.  As an example, I remember 208 pin TQFP packages that were, with leads, something like 32x32mm, in contrast the 20x20mm i.MX6 is 624 pin.  So what would you like to sacrifice in order to avoid BGA? space and how many features?

  • They're not cheap and are 58mm x 17mm, but take a look at Gumstix: https://store.gumstix.com/index.php/category/27/

     

    As selsinork said, you're paying for a board with lots of layers and microvias and tight tolerances.  The trade-off is that you get to make a cheap base board for everything else.

     

    You often see these things at linuxgizmos.com (formerly linuxdevices.com).  They usually don't indicate pricing, which is very annoying.

  • in reply to johnbeetem

    Hi John and agrahambell ,

     

    I must admit, the post was partly triggered by seeing the mentorel page. I think it may be around 50x40mm from the photos. If there was a design with no HDMI or Ethernet, I was curious how much smaller it could go. I agree on the connectors issues. One solution could be to use edge solder type method, like this:

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    However, then only one side of the board can be populated (unless there is a cutout in the mother board), which may be impossible for compact high speed designs. So, one sacrifice could be amount of I/O, and have a few high speed interfaces like SPI, thus reducing the connector pins.

    At this tiny size, HDMI and Ethernet could be sacrificed, because those ICs are available in non-BGA, and could semi-easily be optionally added to the mother board, if people required them, as well as microSD.

    Some people may be happy with WiFi for example, and not need Ethernet. Replacing with WiFi minus the antenna would be a good idea, because a board this size would probably not always be fitted in a device with a large Ethernet connector, but WiFi should ideally replace it.

    The Nano is getting there, it picked the performance as the sacrifice.

    the Gumstix actually look very good, as you say the price is still high, for the reasons you mentioned, but the size is not bad - in terms of area it is only slightly bigger.

    It was interesting to see which processors they chose.

    If you guys had to pick a device today (BGA) to try and fit on such a compact SOM, which would you pick? Probably a Sitara or OMAP I guess?

    Also, thanks for the linuxgizmos link - I noticed an 'Ingenic Newton' there, which is MIPS based and tiny, but no pricing. Still, it is encouraging to see that such compact platforms are possible.

    I wonder what kind of pricing Edison is targetting.

  • in reply to johnbeetem

    John Beetem wrote:

    They usually don't indicate pricing, which is very annoying.

    If you need to ask, you probably don't want to know image

     

    The prices of most/all of these SOM modules has the unintended consequence that the BBB is out of stock everywhere... $200 vs $45 probably means you can afford to make the case a bit bigger...

  • in reply to shabaz

    shabaz wrote:

     

    Some people may be happy with WiFi for example, and not need Ethernet. Replacing with WiFi minus the antenna would be a good idea, because a board this size would probably not always be fitted in a device with a large Ethernet connector, but WiFi should ideally replace it.

    Have you seen the typical WiFi/BT modules as used on the wandboard and cubietruck ?  They're not far off using the same board space as a RJ45 connector.

    Orthogonal problem to that is SOM is usually aimed at industrial use where the requirement is much less likely to be wifi. WiFi = consumer, mostly.

     

    The problem with the Nano is that the compromise was in not using a BGA. If you've read the olimex blog you'll know that the choices are quite limited when you do that.

     

    Personally I probably wouldn't try to fit anything, bga or otherwise, on anything so small. Or maybe something like a Cortex-M*   Once you're putting linux on it I'm much more inclined to think you'll be wanting a display and various other stuff that'll make the size constraints less of a problem

  • in reply to shabaz

    shabaz wrote:

    At this tiny size, HDMI and Ethernet could be sacrificed, because those ICs are available in non-BGA, and could semi-easily be optionally added to the mother board, if people required them,

    It's a compromise.. the AM3359 needs that external HDMI framer chip, the i.MX6 has it on-chip already. They both have on-chip MAC, just the PHY that's external to give the flexibility of cost savings by only implementing 10/100 vs 1000.

    You may also need to sacrifice other things, the OLinuXino-LIME has (IIRC) only a 16bit DDR interface which leads to performance compromises - it's marginal on memory bandwidth for video.

     

    So as you start going down these roads, you need to have a clear idea of what you need ahead of time. That way you can pick the compromises that make sense for your particular application.

     

    How do you weigh up a 30x25mm module that gives you 30% of everything at $200, compared to a 50x30mm one that gives you 99% and costs $50 ?

  • in reply to Former Member

    It's hard knowing what to compromise, and if it would be worth it. I suspect if HDMI and Eth PHY were removed, the BBB reference design could be brought down to about 40x30mm from the approx 50x40mm that the mentorel board looks like currently. The flash and DRAM take up a fair bit of space. Whether it can still be done in 6 layers (like the current BBB) I'm not sure. The WiFi + Bluetooth solutions will take up additional space, of the same order as the Eth port, this is true.

    I'm no expert at the CAD package used for the reference design sadly, otherwise I'd try to delete the mentioned bits and see how much still remains routed in a usable way near the processor and memories, just for curiosity's sake.