hi anders,
my first observation is that if you want to put together a
single-purpose application, then boilerplate isn't a very good place to
start; it's pretty complicated so as to demonstrate many different
sensing combinations. you might want to look at simpleaccel instead,
and change the analog source to ecg; it will make adding changes much
more straight-forward, and simplify debugging quite a bit.
that said, if you want to use software for timestamps, then use localtime.
also bear in mind that there's a latency penalty introduced by atomic
code blocks (iirc, about 22 ticks for just the setup and teardown of
atomicity, plus code).
i hope that this helps,
steve
On 05/13/2011 10:04 AM, Anders Sørensen wrote:
Hi all,
I'm looking to get a rough estimate of the execution time of the
'triggerConversion' in the BoilerPlate sample firmware. In my case, this
function reads ECG data from the memory area it resides it, converts it to
digital values, and makes the converted data available through DMA.
My idea is to get a timestamp from the instant the timer event fires, and then another
timestamp when the "DMA is done" event is handled. My approach is described in
detail below.
In the BoilerPlateC.nc file, the 'event void SampleTimer.fired()' function is
called whenever the sampler timer fires - in my case it's every 20ms (50Hz).
I use a Counter<TMilli, uint16_t> counter to get this. All good, and the
values make sense and are proper, i.e. the timer actually fires at the given rate
(50Hz).
Once the DMA is ready, it fires the asynchronous event 'async event void
DMA0.transferDone(error_t status)' function in BoilerPlateC.nc.
As mentioned, I also capture a timestamp from the same counter here.
And this is when it gets weird. Every timestamp pair (timer fired and DMA
ready) are equal. If I am measuring these timings correctly, this means either
1) the clock's resolution is not high enough to capture the time elapsed from
_before_ calling 'triggerConversion' to when the data is available through the
DMA,
2) the execution time of 'triggerConversion' is actually below 1ms, which
leads to 1) again.
I have tons of thoughts about what could be wrong, but can someone point me in
the right direction?
Thanks in advance.
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