[Tinyos Core WG] Meeting: 5/30

[Prabal Dutta]

What does it mean to group and sample together the temp and humidity
sensors on Telos if they are accessible only serially?  Similarly,
what does it mean to sample the TSR and temp, if the first has an
acquisition time that is one to two orders of magnitude lower than the
latter?

With regards to dynamic grouping, this approach would required the
user to define val_t structs for the power set of sensors on each
platform, wouldn't it?  That is cumbersome and doesn't seem very
portable.  Other options, for example using untyped byte arrays to
pack readings, is error prone and statically uncheckable.

If you assume that you're giving up portability, then instead of
parameterizing using val_t, you could provide all of the Read (or
Notify) interfaces by the generic component and use a runtime
mechanism of specifying which subset to sample.

- Prabal

On 5/31/07, Kevin Klues <klueska at gmail.com> wrote:
>
>
> > For example, on the
> > msp430 ADC the HAL client "Msp430Adc12ClientC" provides the
> > "Msp430Adc12MultiChannel" interface which does exactly what we are
> > talking about. A simple wrapper could map this to a "HIL" without the
> > need for a GroupedSensorsP that "cycle(s) through 'numSensors'
> > requests in a for loop for all connected Resource interfaces, waiting
> > for them all to be granted before issuing a read() command on all of
> > them concurrently."
>
>
> The idea behind the GroupedSensors component is for grouping multiple types
> of sensors together -- not just those that rely on access to the ADC.  Its a
> way of ensuring that the sensor reading you take are correlated in time in
> some way.  For example, on the telos, you can issue commands to sample the
> humidity and photo sensors concurrently, but you can't do the same for
> humidity and temperature -- these have to be sampled serially since they
> require access to the same hardware chip.
>
> GroupedSensors would just be a way of conveniently specifying which sensors
> you want to take samples from together so you don't have to mess with
> grabbing hold of resources and managing the state required to sample
> multiple sensors at once.
>
> In regards to sampling sensors (2,5,6) obviously these would need to be
> mapped to some platform specific (or sensorboard specific) sensor
> identifiers... you wouldn't just use the raw numbers themselves.
>
>  Kevin
>
>
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