[MinnowBoard] 4GB Ram need pcb rerouting?

[John Hawley]

Inline -JH

On 06/16/2016 01:47 PM, Joe Tom Collins wrote:
> Is the board really than much smaller than an SO DIMM?
> The specs I have for the Turbot are 99mm x 74mm
> And SO-DIMM comes in 68mm round numbers.

I don't have a SODIMM handy, but the connector would chew up a fair
chunk of space on the existing board (I can try and get a picture this
evening if it would help)

> This is why I suggested it be on a shield with a separate RAM Expansion
> connector.

Not a bad idea, just tough to do "right" since the memory lanes tend to
be the trickiest and hardest to route for most boards.

> I know things are tight, but what if expansion was ENTIRELY on a shield
> with a SO-DIMM Slot or two?

Probably would need a LOT wider expansion header, paper napkin math
means we'd go from a 60pin HSE connector to something like an almost 300
pin connector (60 + 204 pins for a sodimm) which, given our current
header, would probably be longer than the Minnow itself.

> The connector would merely expose the processor's normal lines for
> addressing RAM, and all the glue to make it work would be on the shield.
> Maybe a plcc type socket directly under the processor. It shouldn't be
> much thicker than the HSE connector, and could provide an HSE
> pass-though while maintaining board size.

Maybe, there's a few challenges though pin count, insertion count, and
overall cost.  PLCC sockets tend to assume that you aren't taking things
in/out a lot, and I'm not sure if there are any that are really rated
for the speeds that memory runs at, does solve the the width issue but
chews up a lot of other board real estate.  Would also need to factor in
the cost of the connectors and the additional board.  At quantity the
sodimm connectors are $3-7/ea, board is probably $5-10/ea, so it's
nearly at least $20 raw parts cost just to manufacture (mind you I'm
paper napkin guessing there, I could be WAY off in either direction).

> I know 32GB was a bit of pipe dream. Even my ITX systems can only handle
> 16GB. LOL.

there's ways of getting there, and even beyond:

http://ark.intel.com/products/77986/Intel-Atom-Processor-C2738-4M-Cache-2_40-GHz

http://ark.intel.com/products/77984/Intel-Atom-Processor-C2718-4M-Cache-2_00-GHz

they just aren't cheap ;-)

> But an 8GB options would be sweet!

Keep a look out, it looks like some folks who are doing manufacturing
are listening.

> Alternatively, is there a way to just put a socket for the RAM chip on
> the board, and let the user upgrade the RAM chips? You could ship with
> 2GB and people could upgrade without SMT soldering gear.

If there was a socketable set of DDR3 chips, it could be an interesting
option, but I'm not sure I've seen / heard of anything like that.  I can
do some digging, see what I can find but I'm guessing they either don't
exist (folks soldering them down), or they are rare enough that they are
substantially more expensive.

> SATA isn't as big an issue for me. MicroSD tech is moving at a good pace
> with speed and capacity.
> Maybe 2 stackedUHS-I/U3 SDXCslots if you can find a connector.

Only gotcha (on the MAX / Turbot), is there's a known bug in the way
UHS-I gets handled in the chipset, and we've had to disable UHS-I as
it's, generally, unstable.  You can turn it on if you want to try it,
specifically:

http://wiki.minnowboard.org/UEFI#LPSS_.26_SCC_Configuration

the DDR50 support, but I'm not sure I've seen a UHS-I card work (if
someone does confirm it's working, please let me know I'd want to double
check it)

As for the dual stacking, we asked a similar question a while back:

https://plus.google.com/b/107232752308803303026/+MinnowboardOrg/posts/KvdRmaGFtek

about SD and eMMC, there was a lively discussion attached to the poll,
and might be worth a look there to see some of our thinking.

> That
> WOULD be cool.
> But since SATA is already in there, I don't suggest removing it. LOL!
> 
> If you DID add a dedicated RAM connector, maybe a SATA chipset that does
> supports port SATA port multipliers
> could go on there to make people who want that happy.

I'll admit, when we first got the MAX prototypes in I though that port
multipliers would work, I'm sad to say they didn't (I had ideas around
it at the time).  That being said, Turbot + Silverjaw + mPCI-E sata
card, in most cases, gets you two SATA-III interfaces with port
multiplier support in them, so it's more doable than you'd expect on the
current board.

> You could even isolate your 12V lines there, since at this point
> everything that requires 12V would be under the Minnowboard.
> 
> On another note... 300 out 100 cool points for being able to get same
> day feedback from the Engineering Dev's!!!!

We do what we can :-)

- John