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 <[EMAIL PROTECTED]> 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 <[EMAIL PROTECTED]> 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 提到: > > 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* < [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>> > 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:[EMAIL PROTECTED] > > <mailto:[EMAIL PROTECTED]>] > > *Sent:* Tuesday, June 19, 2007 4:20 PM > > *To:* David Moss > > *Cc:* [email protected] > > <mailto:[email protected] > > > *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* <[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>> > 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:* [EMAIL PROTECTED] > > <mailto:[EMAIL PROTECTED] > > > [mailto:[EMAIL PROTECTED] > > <mailto: [EMAIL PROTECTED]>] * On Behalf > Of > > *roberto pagliari > > *Sent:* Tuesday, June 19, 2007 3:24 PM > > *To:* [email protected] > > <mailto:[email protected]> > > *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 > > [email protected] > > > https://mail.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help >
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