On Oct 14, 2008, at 4:53 AM, Mustafa Hammad wrote:
> Good morning,
>
> I am studying tasks execution time in TinyOS 1.x with mica2 platform.
> I have implemented a command that read the HW counter (TCNT0) by
> using clock interface. The default counter scale is 1024 ticks/
> second. I changed this scale to be 32768 ticks/second to get more
> accurate measurements.
>
> Task code is instrumented to be something like this:
>
> task void processing()
> {
> start_at = call ReadHWcounter();
> …..
> …..
> end_at = call ReadHWcounter();
> }
>
> The different between these two variables present the task execution
> time. Each cycle is equivalent to about 33 microseconds.
>
> I used the avrora simulator to verify my measurements which showed
> that there are some differences. For example, a task which toggle
> the three LEDs 30 times takes 10 counter cycles (i.e. about 0.00033
> second). But in avrora simulator it takes about 0.000982 second.
>
> I don’t know what I am missing?
> Is there any other way to verify my measurements?
>
> Thanks in advance,
> Mustafa
>
The fifth paragraph of the TOSSIM manual:
Time: While TOSSIM precisely times interrupts (allowing things like
bit-level radio simulation), it
does not model execution time. From TOSSIM’s perspective, a piece of
code runs instantaneously.
Time is kept at a 4MHz granularity (the CPU clock rate of the rene and
mica platforms). This also
means that spin locks or task spin locks will never exit: as the code
runs instantaneously, the event
that would allow the spin to stop will not occur until the code
completes (never).
Phil
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