[Tinyos-help] about CC2420

[roberto pagliari]

Hi Tsung,
regarding your last question I read on CC2420 that the RSSI_VALID status bit
is set when the receiver has been enabled for at least 8 bit symbols, so I
believe the value you retrieve is already averaged over 8 symbol periods

On 6/19/07, Tsung-Han Lin <b90901046 at ntu.edu.tw> wrote:
>
> In TinyOS 1.x you can connect the interface HPLCC2420 to HPLCC2420C and
> use
> call HPLCC2420.read(CC2420_RSSI);
> to acquire ambient RSSI, make sure you check the RSSI_VALID register
> before you read out the value.
> To check that register you'll need to read the status byte, you can use
> call HPLCC2420.cmd(SNOP);
> In CC2420RadioM.nc you can find some examples on how to handle this
> status byte.
>
> Yes CC2420 will continuously update the rssi reading in RX mode. The
> sampling rate, isn't the datasheet said the chip would give you a
> reading for each symbol but the reading is averaged over the past 8
> symbol periods?
>
>
> -Han
>
> roberto pagliari Ìáµ½:
> > 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 <mailto: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 ¨C 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
> >     <mailto:bobtinyos07 at gmail.com>]
> >     *Sent:* Tuesday, June 19, 2007 4:20 PM
> >     *To:* David Moss
> >     *Cc:* tinyos-help at millennium.berkeley.edu
> >     <mailto: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 <mailto:dmm at rincon.com>>
> wrote:
> >
> >     The default mode for the radio is Rx mode ¨C 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) ¨C 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>
> >     [mailto: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
> >     <mailto: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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> > Tinyos-help at Millennium.Berkeley.EDU
> >
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