[Tinyos-help] Re: [Tinyos-devel] DAC and MSP430RefVoltGenerator in T2

Sandip Bapat sandipbapat at yahoo.com
Thu Feb 14 08:14:30 PST 2008


In the latter approach you outlined, where they share the same arbiter, if we assume that the ADC and DAC require the same reference voltage, would they still not be able to run in parallel? 

Here's one scenario which might be common to a lot of sensing apps: An app uses RefVolt via Msp430AutoRVGClient to do its sensing and requires some reference (say 2.5V). Occasionally, the app also needs to use the DAC, with the same reference voltage, for instance, to change the gain setting on the sensor by varying the DAC voltage. If both used the same reference, could they still not work in parallel? 

Also, the DAC has a 3x multiplier setting so effectively it can produce the same range of outputs regardless of what reference voltage is being used by others (ADC). We could (re)implement the getState() function in RefVolt so that the DAC client can figure out which, if any, reference voltage is being used by the ADC and scale its inputs accordingly.

But perhaps I'm missing something even more fundamental here as to why they can't run in parallel.


----- Original Message ----
From: Jan Hauer <hauer at tkn.tu-berlin.de>
To: Vlado Handziski <handzisk at tkn.tu-berlin.de>
Cc: TinyOS Development <tinyos-devel at millennium.berkeley.edu>; "tinyos-help at Millennium.Berkeley.EDU list" <tinyos-help at millennium.berkeley.edu>
Sent: Thursday, February 14, 2008 10:42:02 AM
Subject: Re: [Tinyos-devel] DAC and MSP430RefVoltGenerator in T2

Currently Msp430RefVoltArbiterImplP intercept the requests of ADC
clients to the Resource interface, it is not really arbitrating access
itself. If the DAC needs access to the RefVolt component too, then we
might need a real arbiter for the RefVolt component that is
independent of the actual ADC arbiter. The drawback is then that for
every ADC/DAC request involving RefVolt we'd need to request two
resources from two different arbiters before the client can start
sampling/outputting. Alternatively we could agree that ADC and DAC
share the same arbiter, which makes arbitration a lot easier, but is
less efficient because you'd never be able to run ADC and DAC in

On Wed, Feb 13, 2008 at 7:53 PM, Vlado Handziski
<handzisk at tkn.tu-berlin.de> wrote:
> The access to the refvolt generator has to be properly arbitrated between
> the ADC and the DAC. Pins, timers, etc. are all potential shared resource
> between the two. Jan, who is responsible for the msp430 ADC stack, is at a
> project meeting and probably has not read the thread. Please get in touch
> with him to coordinate. No #ifdefs please :)
> Vlado
> On Wed, Feb 13, 2008 at 6:43 PM, John Griessen <john at ecosensory.com> wrote:
> >
> >
> > Sandip Bapat wrote:
> >
> >  a DAC module would either have to wire to Msp430RefVoltArbiterP (in which
> case it also has to provide the
> >
> > AdcConfigure interface) or be expected to provide wiring for these
> interfaces.
> >
> > This is fine for apps that just want to use the DAC and not ADC but what
> if both are used and the
> >
> > ADC is already using Ref Voltage ? I guess we could use #ifdefs in the DAC
> but wouldn't having
> >
> > a Msp430RefVoltArbiterC that does the wirings required for
> Msp430RefVoltGeneratorP be better?
> >
> > The best thing would be to create new function in the RefVoltArbiter so it
> can stay on after an ADC12 or
> > Dac12 call has requested it if another request is heard within a time
> period.  As far as I can tell,
> > Dac12 and Adc12 of a MSP430F1611 can both be going at once.
> >
> > John Griessen
> >
> >
> > --
> > Ecosensory  Austin TX
> > tinyOS devel on:  ubuntu Linux;  tinyOS v2.0.2;  telosb ecosens1
> > _______________________________________________
> > Tinyos-devel mailing list
> > Tinyos-devel at millennium.berkeley.edu
> > https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-devel
> >
> >
> >
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