On Tue, May 16, 2017 at 8:28 PM, Vincent ml.eoma68@eml.cc wrote:
Hi Luke,
Okay, it is good to see you on the same page when it comes to KiCad vs. Altium.
yeah... ismo too. he tried it... basically anyone who's ever used a professional CAD package will scream in horror and try to dig out their own eyes rather than use it :)
Also, I wanted to give the community the chance to respond to this prior to making any design.
awesome.
I highly appreciate your effort in creating the template version of the i.MX7 design. I hope I can carry it on in your best interest without touching anything of the critical stuff.
great. i'll send it your way. it should be pretty obvious what's needed. i *think* you might, unfortunately, need to rotate the eMMC chip by 45 degrees (one way or the other) so as to make room for the PMICs (without needing to do too much to the actual PMIC layout... which i *don't* recommend altering if you can possibly help it). but to do _that_ you might also need to move one (or both) of the XTALs. the "safest" one to move is the 32khz one - maybe replace that with an MC149 footprint one (i think that's what it is: take a look at the EOMA68-A20 board layout). maybe MC-146? anyway doesn't matter.
one thing that will need sorting: the 5V DC input. i haven't completely finished that, i have however removed "battery" and other stuff from the Reference Design, we'll need to go over that and make sure it's clean/clear.
Do you by accident know how critical the layer stack-up is in terms of material selection, e.g., in terms of using FR4 and having controlled impedances by the manufacturer?
ok to give you some idea: DDR3 tracks which @ 3.2mil are nominally 100 ohms on a 6-layer stack on FR4 @ 1.6mm will drop to **HALF** that amount if you convert to an 8 layer stack @ 1.2mm.
*luckily* this is something that has been catered for in the actual DDR3 standard, so you can have 40 ohm, 60 ohm, ... all the way up to 120 ohm impedance, and the DDR3 termination at *both* the PHY *and the actual DDR3 ICs* can be changed in software.
for the USB2 tracks, honestly they are so short that i wouldn't worry about it. just get them out on as few layers as you can with as little modifications as you can, leave them @ 3.5 mil with spacing around... 7 mil and be done with it. just make sure that you set up equally-spaced vias all the way. general rule is: the more "artistic" (i.e. the more "beautiful") the design, the greater the chances are that it will work. yes, really! symmetry and beauty bizarrely have a better chance of success than any amount of "engineering rules"!
also *do not* put tracks close to high-speed signals, not even on another layer. if you absolutely absolutely have to put signals (any signals) on neighbouring layers, make damn sure that they "cross" - don't for goodness sake make them go "parallel".
For testing purposes etc., it would certainly be much easier to use a manufacturer that happens to be nearby.
... yyyeah... except i can guarantee they'll be charging you around $2k to $4k for QTY 10 PCBs instead of only $USD 600 to 800, and god knows what western PCBA (pcb assembly) rates are. don't be surprised if they quote you north of $USD 10,000.
given that it's going to take at least 3-4 weeks for the PCBs and assembly to be done _anyway_, what's adding the cost of a DHL courier going to be? $70 plus import duties? is it *really* that important to do "testing" that you don't want to save a whopping $8k difference in the cost??
Also, I wanted to point out that the i.MX7 security manual is only available under an NDA (one needs to sign up and request the file download). I'm actually wondering why this is the case because the stuff in there is not that special after all.
bizarre! well, one thing you might want to investigate: does that NDA conflict with releasing source code or not?
Thanks for summarizing all the other aspects (power profile, etc.).
no problem vincent.
l.