[Tinyos-help] about CC2420

[roberto pagliari]

thank you David. I misunderstood the datasheet information regarding the CCA
modes. But it is possible, not during the transmission, to get the rssi
data, no matter if the node is receiving or not a message? I just need to
monitor the environment, but I'm not sure if in RxMode the receiver measures
the RSSI value even if a preamble is not detected. Do you know if it does
and the rate of RSSI sampling?


thanks a lot again!

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