[Tinyos-help] about CC2420
roberto pagliari
bobtinyos07 at gmail.com
Mon Jun 25 17:07:05 PDT 2007
before testing some code that simply measures the rssi I just need to know a
thing. When I get the RSSI value from the cc2420 register, or if I simply
want to know if the rssi is greater then the cca threshold, using the call
TOSH_READ_RADIO_CCA_PIN(), I know that this takes 8 symbol periods. Two
questions:
1) why does in cc2420M.nc the call TOSH_READ_RADIO_CCA_PIN() does not wait
for the RSSI_VALID flag?
2) if the radio doesnt transmit for a long time, the RSSI is continuously
updated every 8 periods of symbol and the RSSI_VALID flag is everytime high,
right?
thanks a lot in advance
On 6/20/07, roberto pagliari <bobtinyos07 at gmail.com> wrote:
>
> 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
> > >
> > >
> > >
> > >
> > >
> > >
> > ------------------------------------------------------------------------
> > >
> > > _______________________________________________
> > > Tinyos-help mailing list
> > > Tinyos-help at Millennium.Berkeley.EDU
> > >
> > https://mail.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help
> >
>
>
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