[Tinyos-devel] Proposed change to the serial stack in TinyOS 2

[David Gay]

On 12/14/06, Matt Welsh <mdw at eecs.harvard.edu> wrote:
> Ben,
>
> > 3) One could add a parameter to the HAL-level put() that signifies
> > that putDone shouldn't come until the UART is idle. This has the
> > benefit of only incurring the cost of spinning when needed, but is
> > confusing, as no one aside from the user of put() can check for
> > idleness.
> >
> > Our proposed solution is the following:
> >
> > 4) Add a split-phase query interface to the HAL with the command
> > wait(). This interface would implement a task-level spin (so that it
> > is interruptable) and would signal waitDone() when the idle flag is
> > asserted. The downside of this interface is that it still relies on a
> > spin, which consumes extra energy as the processor will not enter a
> > sleep state while waiting.
>
> I like it. I would suggest not using a new interface for this (unless
> one is strictly necessary - why not add the command/event to the
> existing UART interface?). And, perhaps to be consistent with more
> commonly used terminology you could call it flush() / flushDone().
> "wait" is a little ambiguous unless you make it clear what you are
> waiting for.
>
> Overall I think this is the right approach as it means you can do the
> 'flush' only when needed.
> It would be good to document under what specific conditions flush
> should be used.

I agree with all of Matt's comments. I would also add before confusion
sets in that the spinning in flush is only necessary on
microcontrollers that don't have a transmit complete interrupt ;-)

David