Currently, it is common to see Contiki's core/ interfaces implementations
spread in both cpu/ and platform/. We here take one step further starting
an effort to centralize all of these in platform's code instead.
This commit starts this by adding platform/galileo/core/ and its sys/
subfolder, adding a stubbed mtarch.h and moving clock and rtimer
implementations to this new folder. From now on we should concentrate
implementation from Contiki's core/ interfaces into the appropriate
subfolder in platform/galileo/core/.
Note that this is not the current fashion followed on other platforms
and cpus folders, as most of them add the core interface implementation
into its subfolder directly. For instance, on CC2538DK,
core/dev/button-sensor.h is implemented in platform/cc2538dk/dev/
directly, while on Galileo it would sit at platform/galileo/core/dev/.
We believe ours is a better approach to organize and escalate a
platform's code base.
We also remove previous x86 mtarch.h and mtarch.c since they weren't used
at all - both native and cooja platforms have their own mtarch
implementations.
This patch adds support for rtimer library on Galileo's platform.
We use the PIT to implement the rtimer platform dependent
functionalities. We chose the PIT for mainly two reason: I) its
configuration is very simple II) it has a high frequency which
provides us a good clock resolution (requirement from rtimer
library).
Since we keep track of the number of ticks in software, we define
rtimer_clock_t type as uint64_t. This gives us a good amount of time
til the variable overflows. For instance, a 32-bit type would overflow
in about one hour for high clock resolution (~ 1us).
The rtimer clock frequency (RTIMER_ARCH_SECOND) is setup to 1 kHz.
There is no technical matter regarding this value. It is just an
initial guess.
Just for the record, we might want to use HPET in future to
implement the rtimer library since it seems to be more appropriate.
The reason why we don't use it at this moment is that, in order to
configure it, we need support for ACPI 2.0 which we don't. Once we
have use-cases for the rtimer library we'll probably replace PIT
by HPET or any other timer more suitable for the job.
