I am trying to understand the CCA code a bit, and this code seems extremely
relevant:
if((last_post == CCA_POST)
&& (*MACA_CLK > last_post_time + 4))
{
GPIO->DATA_RESET.GPIO_43 = 1;
if(bit_is_set(*MACA_STATUS, maca_status_busy)) {
GPIO->DATA_SET.GPIO_06 = 1;
maca_busy = 1;
last_post = NO_POST;
} else {
GPIO->DATA_RESET.GPIO_06 = 1;
maca_busy = 0;
last_post = NO_POST;
}
last_post = NO_POST;
last_post_time = *MACA_CLK;
}
So, it looks like a clock periodically drives MACA status updates. On a
status update, a bit is checked to see if the channel is busy or not?
(if(bit_is_set(*MACA_STATUS, maca_status_busy))). If it is busy, the
relevant variables are set.
What's the significance of "4" here? (last_post_time+4). Also, is the
sensing tunable? Can I adjust the threshold which determines whether the
channel is busy or not within MACA? Making it more or less sensitive,
basically?
Thanks for the help!
- George
On Sun, Sep 18, 2011 at 3:45 PM, <[email protected]> wrote:
> On Sun, Sep 18, 2011 at 03:30:22PM -0700, George Nychis wrote:
> >
> > Hi Mariano,
> >
> > So, I've been reading through some of the code. It looks like this is
> not
> > implemented:
> >
> > int contiki_maca_channel_clear(void);
>
> Are you looking at the contikimac-oldcfg branch? That should have it.
>
> >
> > What is exposed by the hardware? Is there a register that keeps an
> updated
> > carrier power value in the current band? That way a threshold can be
> placed
> > against it?
>
>
> As far as we know, no. I'm using the CCA sequence provided by the MACA.
>
> >
> > I guess i'm just looking for advice on the basic CCA building block
> locations,
> > and then I can build carrier sense and exponential back off around them.
>
> Check out that branch --- it has a start of what you need in
> maca.c. see post_cca() and cca().
>
> -Mar.
>
>
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