Hardy Griech wrote:
Grant Edwards wrote:
On 2007-11-14, Grant Edwards <[email protected]> wrote:
:
Protothreads looks promising:
http://www.sics.se/~adam/pt/
Thanks for the inspiration, Grant!
At the moment I'm looking for a light-weight mechanism for doing
'multi-threading'. Protothread could be one way to do it.
I'm yet struggling a little bit with low power modes. How could this be
implemented with protothreads?
To me it seems that protothreads are doing some kind of active wait.
And that's definitely not my goal, because the device should be battery
driven.
The trick is to invoke the protothread only when there is a chance that
the protothread will do something else than waiting. When no protothread
should be invoked, the system can go into low power mode. For example,
you can check the return code from the protothread to distinguish from
protothreads that are waiting and those that have yielded. Based on this
information, you can decide to for example go to sleep when all
protothreads are waiting, or when all protothreads have yielded.
This is the approach taken by Contiki (http://www.sics.se/contiki/). A
Contiki process consists of, among other things, a protothread. This
protothread is invoked when another process posts an event to the
process, or when an interrupt handler has requested the process to be
invoked (polled). For example, there is a timer interrupt that polls a
process that performs more complex timer management.
When no messages are to be delivered, and when no interrupt has
requested an invocation, the CPU is set to low power mode. The central
loop looks something like this:
while(1) {
invoke_protothreads_that_needs_to_be_invoked();
if(event_queue_length == 0 && num_process_that_needs_a_poll == 0) {
LPM();
}
}
The watchdog can be kicked in this loop as well.
/adam
--
Adam Dunkels <[email protected]>
http://www.sics.se/~adam/
