Hi Eric
Up to now, it doesn't work. In fact, when it is supposed the piece of code
executes, the mote resets, and I cannot understand it! I'm also debugging the
code but I'm missing something because I don't see anything strange.
Lets see if I understood your doubts. In relation to who keeps track of what
buffers are available or not, I thing that functionality is part of the QueueC
component and yours. Yours because you are who mark when a packet has to be
dequeued aimed at being transmitted or discarded, and of the QueueC because it
points to a "free" space of memory where you can enqueue a new packet as well
as the head of this queue. On the other hand, when you need to enqueue a new
packet, you have to return a empty message_t to the MAC by making a call to
Pool.get(). Then, you enqueue the packet by calling
Queue.enqueue(new_message_t) . Both components, PoolC and QueueC, point to
different spaces of memory but they keep track of if you have space to store
more packets, the piece of memory where you enqueue/return a message_t... . And
when you dequeue a packet, after the event sendDone(msg) is signaled, you make
a call to Pool.put(msg) (I'm sure you're aware of this). This make sense for
me, but as I said, for now, it doesn't work!
Regards
David
Date: Tue, 27 Nov 2012 16:31:15 -0800
Subject: Re: [Tinyos-help] Drop packets in TinyOS
From: cire...@gmail.com
To: drod...@outlook.com
CC: tinyos-help@millennium.berkeley.edu
On Tue, Nov 27, 2012 at 12:16 AM, David Rodenas <drod...@outlook.com> wrote:
Hi Eric
In any case, I have a possible answer which is simpler than I thought. I was
addressing the problem wrong, thinking that a message that was enqueued, it was
really a peace of dynamic/external memory that came (was transmitted) to the
receiver node, so it increased the already occupied memory (there is a reason
of why a thought this: I also work with Network Simulator 2 - NS2 - and there
you use dynamic memory for messages). This is totally wrong with TinyOS, when
you receive a data message and enqueue it, you are only copying the whole
content to the corresponding memory location (you defined Queue as static
memory) and increasing a counter of enqueued messages. Then you can use PoolC
to return an empty message_t to the system. Thus, when you make a call to
Queue.dequeue(), what this function returns is a pointer to a static portion of
memory (of size message_t) as well as decreases the counter of messages
enqueued. Therefore, when another message_t is enqueued, this occupies the same
portion of memory so the node never run outs of memory because of what I what
asking.
Am I right?
The gist is certainly correct. The devil as always is in the details.
I do hand debugging of code like this to make sure that a) the general case
works, b) is argueably correct, and then c) examine the corner cases (where can
it screw up, and are there assumptions made about how the code works that can
be violated). But I didn't write or test this code.
so your mileage may vary (YMMV).
But I do think you have the gist of how it behaves.
The question is who keeps track of what buffers are available and what denotes
the buffer being busy. If you dequeue the packet from the "queue", does it
something else need to be told that this packet is available? Should it get
put back into the Pool?
eric
Thanks again, regards
David
Date: Mon, 26 Nov 2012 19:51:48 -0800
Subject: Re: [Tinyos-help] Drop packets in TinyOS
From: cire...@gmail.com
To: drod...@outlook.com
CC: tinyos-help@millennium.berkeley.edu
Looking at this problem from the queueing mechanism is coming at the problem
from the inside out.
So it is pretty difficult trying to answer the question you are asking.
To do so really requires looking at the data flow (message_t) and buffer flow
at various points in packet transmission and reception.
The answer to your question depends on what the original caller of the enqueue
wants done. And then there is the whole wiring issue and how to pull the
whole thing together.
Simply dequeuing the message certainly isn't enough because that most likely
leads to lost messages. But the whole scheme needs to be worked out in a
systemic fashion. And it would be nice if it were documented. It certianly
is a hole. Eventually I'll get to it.
I certainly understand what you are trying to accomplish. Been there done
that. Sorry I don't have a better answer for you.
eric
On Mon, Nov 26, 2012 at 7:48 AM, David Rodenas <drod...@outlook.com> wrote:
Hi all
I would like to know how to discard a message which is stored in a queue
(component QueueC of message_t). To better explain this, lets suppose we have a
maximum number of retries during we are trying to forward a data message. This
is stored in a queue waiting for being transmitted. A failed transmission can
occur due to collisions, interferences, etc. So when this maximum number is
reached, the data message should be discarded, making this same procedure with
the following message (head of the queue). Here there is a simple code of what
I'm asking:
maximum_retries = 3;num_retries = 0;
if (num_retries > maximum_retries){ message_t * drop_msg = call
Queue.dequeue(); drop(drop_msg);
}
The point is that I'm not sure if just dequeuing the message_t is enough. This
message occupies a piece of memory space and this has to be freed. Am I right?
Should I use the function free as in any C-based language when dynamic memory
allocation is used?
Thanks
David
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Eric B. Decker
Senior (over 50 :-) Researcher
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Eric B. Decker
Senior (over 50 :-) Researcher
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