Re: Getting started with bare-board development

[antispam@math.uni.wroc.pl]

Adam Jensen <hanzer@riseup.net> wrote:
> Hi, I've recently began to have a serious look at Ada-2012 and
> Spark-2014, and using GNAT for the development of real-time software in
> embedded systems.
<snip>
> Adacore has an example for the STM32F4-Discovery[3], and more elaborate
> documentation is available for the Nucleo[4], but both of those kits
> seem to have very limited memory. How much can be done with that?

Just to address this point: real time embedded systems are frequently
done with single chip microcontrollers.  Microcontroller contains
combinatorial logic (processor core, digital peripherials),
SRAM, flash and analog parts.  Having all this on single chip
brings substantial advantages.  But the drawback is that
various parts have conflicting manufacturing requirements.
So no part is as good as "pure" chip could be.  In particular,
microcontroller at lower end may have as little as 32 bytes
of RAM and at high end rarely go into megabyte range.
Basically, if you need more RAM you need to go into multi-chip
design with separate memory chip.  Then you can easily get
say 256 MB, but latency of external memory is much larger
than internal SRAM.  So while you may have plenty of
external memory program using it will run slower.  Worse,
high latency means that it is hard to give assurance
of real time behaviour.

STM32F4-Discovery contains relatively large microcontoller.
Nucleo boards have several versions containg both middle
sized and large microcontollers.

Note that flash is typically much larger than RAM, so
in fact you can have quite a lot functionalty inside
a single chip microcontroller.  When talking about
critical system I would say that modern microcontollers
give you quite a lot of space where bugs can hide.
In other words, to limit effort spent on validating
code you may wish to limit size of your system so
that in effect it fits in small device.

-- 
                              Waldek Hebisch