[Tinyos-devel] Re: [Tinyos Core WG] time sync interfaces

[Vlado Handziski]

On Dec 19, 2007 5:30 PM, John Griessen <john at ecosensory.com> wrote:

> David Gay wrote:
> > On Dec 18, 2007 5:15 PM, John Griessen <john at ecosensory.com> wrote:
> >> To be a HIL, the app can't use specific timers, so it will be limited
> to
> >> using feedback to correct errors and may have lots of jitter.  It's not
> going to be
> >> smoothly nudging the time, since it is the same app for all different
> hdwe.
> >
> > A misunderstanding here: a HIL timesync implementation doesn't have to
> > be portable, it just has to offer the same interface on all platforms.
>
> I read the intent of HILs to be separating the hardware dependent from the
> non.
> Hardware Independent Layer vs. Hardware Presentation Layer means HIL same
> interface and code for all;
> Hpl means different per platform and per sensorboard interface and code
> for maximizing performance of specific hdwe.
>
>  From TEP 2:    http://www.tinyos.net/tinyos-2.x/doc/html/tep2.html
>
> "The final tier in the architecture is formed by the HIL components that
> take the platform-specific abstractions provided by the
> HAL and convert them to hardware-independent interfaces used by
> cross-platform applications. These interfaces provide a platform
> independent abstraction over the hardware that simplifies the development
> of the application software by hiding the hardware
> differences. "
>
> So HIL is pretty close to portable, not the exact meaning of "can be
> moved", but very
> similar in, "convert them to hardware-independent interfaces"
>
> Clarification?  Were you meaning portable as in, "a port to a new
> platform"?
> Where new code needs to be written at HAL and HPL levels?  I still think
> the best kind of HIL
> cross platform time sync app would "just work" on a new platform after the
> developer of same
> creates  HAL and HPL level code dealing with time and timestamping.
>

David is just pointing out that while the HIL interfaces are portable, the
implementation of these interfaces (the HIL component) does not have to be.
I.e. the HAA does not constrain you in how you transform the
platform-specific HAL interface into the platform-independent HIL interface.
Each platform can have its own HIL implementation on top of the platform
HAL. But in many situations, a common structure can be used, allowing some
sharing of the HIL implementation across the platforms.

Vlado
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