April 2015
32
E
MBEDDED
C
OMPUTING
How to select the right
modules in the embedded market?
By Wolfgang Heinz-Fischer,
TQ-Group
It has been decided to use a module
- now comes the much more difficult
part of the decision – the search for
the best solution. The number of
modules offered in the embedded
market is nearly incalculable. So, how
do I find the optimal module for my
requirements?
First of all, there is obviously the question
whether there is a module in the market for
the selected processor or whether another
processor, for which a module is o ered,
could also suit. In principle, one must distin-
guish between modules with an x86 processor
and the other architectures. Here, there are
fundamental di erences between the market
and the supply side. When it comes to the
x86 modules, there are actually only the stan-
dards, today with COM Express and Qseven.
e industry standards ETX and XTX have
aged a bit, but they are still o ered in the mar-
ket. Even Single Board Computer (SBC) are
still o ered, which are absolutely su cient
for some applications. However, the ques-
tion sometimes is about the long-term supply
availability in the same form factor and in the
same design. If the plugs actually remain at
the same position, can I install an SBC in my
machine for a long term without alterations?
is is basically the question of the stan-
dard. To what extent is the standard actually
described and xed and how many degrees of
freedom are allowed? e main expectations
from a standard are surely the interchangeabil-
ity of the systems of di erent suppliers and the
scalability in order to be able to easily adapt
to various requirements. If the standards meet
the expectations, they are de nitely helpful
and practical. How close do the o ered stan-
dards come to the dream of an absolute stan-
dard, or how o en you are disappointed that
the expectations are unfortunately not met in
the actual use?
Standards in the embedded market promise
that all modules, which follow this standard,
are compatible and thus interchangeable. For
the user, this means that they develop an
application board, which follows the standard,
and can then choose from di erent manufac-
turers and simply attach the module. If they
require more power, they simply take the
correspondingly more powerful module of a
manufacturer and replace the existing module.
is sounds good; but the reality is di erent
and in 90 percent of cases, it is necessary to
adapt or modify the application board.
Actual interchangeability in all cases is possible
only where the standard is restricted to a very
narrowly formulated speci cation of func-
tions. is mainly includes PC/104, in which
only the ISA and PCI Bus are xed; all other
functions are realized more or less through a
manufacturer-speci c plug grave. e situa-
tion is similar in case of MicroTCA and other
telecom standards. On the other hand, if you
have a good look at the COM Express stan-
dard managed through the PICMG, it quickly
becomes apparent where the limits of a clearly
described standard lie.
In case of x86 modules, all processor func-
tions are mapped; i.e. they are available at the
plug. However depending on the processor or
the chip set, not all functions de ned in the
standard can be mapped, since these are not
delivered by the processor/chip set. For exam-
ple, in the COM Express standard 8x USB 2.0
interfaces are de ned, which are however sup-
ported by very few processor/chip set combi-
nations. Inmost cases, 4 to 6USB 2.0 interfaces
are available. Even the 24 PCI Express Lanes
de ned in the COM Express standard Pinout
version 2 are, in all probability, not fully sup-
ported. An Atom processor for example deliv-
ers only 2 PCI Express Lanes x1. is means
that I can attach the same module, e.g. COM
Express Compact with a Core processor, in an
application board which was developed for an
Atom design; but I do not use the additional
PCI Express Lanes.
e same restriction is applicable the other
way round. An application board optimized
for a Core processor will not support all func-
tions when using a module with an Atom pro-
cessor. e x86-module market is easier when
it comes to supporting so ware drivers and
does not make it too di cult to switch over
to another module. e corresponding driv-
ers should normally be downloaded from
the websites of the chip manufacturers. us,
while it should be carefully checked even in
Figure 1. Proprietary module
TQMa28 with ARM processor
