[Tinyos-help] about CC2420

[David Moss]

Actually, you have an option to transmit without CCA.  At the hardware
level, there are two command strobes to transmit the contents of the TXFIFO:
STXON and STXONCCA.   If you simply toggle STXON instead of STXONCCA, then
your packet gets transmitted no matter who else is transmitting. 

 

There is one other software driver issue to overcome in TinyOS though - the
radio stack driver does its own backoff and CCA checking by default.  You'll
need to disable this, probably through MacControl or CsmaControl or
something.. I forget what it is in 1.x.

 

-David

 

 

  _____  

From: roberto pagliari [mailto:bobtinyos07 at gmail.com] 
Sent: Tuesday, June 19, 2007 4:20 PM
To: David Moss
Cc: tinyos-help at millennium.berkeley.edu
Subject: Re: [Tinyos-help] about CC2420

 

right, I just remembered that point in the cc2420 datasheet. I have a last
question: the transmission of a packet is performed if the RSSI value is
greater than a certain threshold, the CCA. The 3 CCA modes are 

0 reserved 
1 clear channel when received energy is below threshold
2 clear channel when not receiving valid IEEE data
3 clear channel when not receiving valid IEEE data and below threshold

I guess the CCA value is a 8 bit unsigned integer 2 complement, so if I need
to transmit a packet, regardless of other transmitting nod I should set the
CCA value to its minimum, lilke -128dBm, or 0xFF. I know during the
reception of a packet the RSSI is averaged over 8 symbols after the SFD has
been detected. During the transmission how does is it calculated? Can I read
it just using the command call function c.. HPLCC2420.read(RSSI_REG)?



On 6/19/07, David Moss <dmm at rincon.com> wrote:

The default mode for the radio is Rx mode - after it transmits a packet, it
automatically switches back to Rx on the hardware.

 

If you attempt to transmit using STXON without clear channel assessments,
then your radio will not only *not* receive the other transmitter's packet,
but it will cause channel interference that will prevent all other motes in
the area from receiving that packet.  That's the point of backoffs and CCA
(clear channel assessment) - determine if the channel is clear before
attempting a transmission.  

-David

 

 

 

  _____  

From: tinyos-help-bounces at Millennium.Berkeley.EDU
[mailto:tinyos-help-bounces at Millennium.Berkeley.EDU] On Behalf Of roberto
pagliari
Sent: Tuesday, June 19, 2007 3:24 PM
To: tinyos-help at Millennium.Berkeley.EDU
Subject: [Tinyos-help] about CC2420

 

hi all,
within RadioControlM I can see CC2420Control.RxMode(), but, after a packet
has been sent I cant find any call to CC2420.RxMode() or SXON oscillator.
where is it done? 

the second question is: once the transmitter oscillator STXON has been
enabled, if an incoming message arrives, will it be lost? 


thank you

 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mail.millennium.berkeley.edu/pipermail/tinyos-help/attachments/20070619/f54e6df5/attachment.htm