{{WarningMessage|text=The information here provided are preliminary and subject to change.}}
==Introduction==
This page provides useful information and resources to system designers in order to design carrier boards hosting '''DAVE Embedded Systems''' system-on-modules (SOM).
These guidelines are provided with the goal to help designers to design compliant systems with '''DAVE Embedded Systems''' modules and they cover schematics and PCB aspects. They apply to several products that are listed on the top right corner of this page (see "Applies to" boxes).
== Basic guidelines ==
In this section basic hardware guidelines valid for all '''DAVE Embedded Systems''' SOMs are detailed.
=== Schematics ===
* Check mirroring and pinout of '''DAVE Embedded Systems''' system-on-modules (SOM) connector* Properly decouple '''DAVE Embedded Systems''' system-on-modules (SOM) power supply with large bulk capacitor and small bypass capacitor
* Use low-ESR X7R capacitor if possible
* Check for correct connection of TX and RX lines
==== PCB Tecnology ====
Use a PCB technology as advised in the following table
* Place bulk and ByPass capacitor near '''DAVE Embedded Systems''' system-on-modules (SOM) power supply pins
* Place series terminator resistor near the related transmitter
If you plan to use the holes as additional retention system, we recommend to pay attention to the mechanical characteristics when evaluating the SO-DIMM mating connectors to be mounted on the carrier board.
== Power-up sequence ==
In order to prevent back powering effects, DAVE Embedded Systems' SOMs provide the signals required to handle power-up sequence properly. For instance, see the recommended sequence for the Bora SOM [[Power_(Bora)|here]].
In case the power-up sequence is not managed properly, the circuitry populating the SOM '''may be damaged'''.
== Interfaces Guidelines ==
This section provides guidelines for the most used interfaces on '''DAVEEmbedded Systems'''s SOMs module. <br/>
Please refer to SOM's detailed pages for specific additional information.
=== Ethernet 10/100/1000 ===
====Case #1: PHY is integrated on SOM====
This section refers to the case of PHY integrated on SOM such as [[:Category:Lizard SOM|Lizard]] and [[:Category:Maya SOM|MayaMAYA]].
===== Schematics =====
* If LAN connector with integrated magnetic is used:
===== PCB =====
'''Refer to this table for 10/100 differential pairs routing'''<br/>
{| {{table class="wikitable" border="1}}"
| align="center" style="background:#f0f0f0;"|'''Parameter for 10/100 differential pair'''
| align="center" style="background:#f0f0f0;"|''' Min '''
<nowiki>**</nowiki>Overall trace length - i.e. Bora + carrier board - should not exceed 10cm. If this is not possible, try to avoid parallel routing in order to reduce crosstalk, and refer them to a ground plane.
One of the main difference between such systems and PCs is that the formers are - if appropriately designed - inherently resilient to sudden power fails (see for example this presentation: [http://events.linuxfoundation.org/slides/2010/linuxcon_japan/linuxcon_jp2010_jung.pdf Application of UBIFS for Embedded Linux Products]).
In any case, system designer should take into account these events and decide if and how manage them explicitly. Here are some typical techniques used to deal with this situation:
* in case the system is used by human operators, the use of clean shutdown - triggered by the user himself - should be encouraged to prevent sudden power off. Technically speaking, this can be done via GUI (soft button) or mechanical device (push buttons and alike). In the latter case, puch push button controllers such as [http://www.linear.com/product/LTC2954 Linear LTC2954] can be very useful to implement this feature
* in case no human operators interact with the system, more complex solutions might be required. This strategy is strongly dependent on hardware characteristics of SOM and must be approached on a case-by-case basis.