[Tinyos-help] RSSI

[Tsung-han Lin]

You don't need to check RSSI_VALID because you do not retreive the RSSI value. The chip would handle the validity of RSSI and inform you whether the CCA check is passed. The CCA check would return bad if the receiver has not yet been enabled 8 symbol period.

-Han
  ----- Original Message ----- 
  From: roberto pagliari 
  To: Marco Antonio Lopez Trinidad 
  Cc: tinyos-help at Millennium.Berkeley.EDU 
  Sent: Wednesday, July 04, 2007 6:58 AM
  Subject: Re: [Tinyos-help] RSSI


  yes, I read it, but within the tinyos code (1.0.7, for instance, CC2420RadioM.nc) there is something like 

    void tryToSend() {
       uint8_t currentstate;
       atomic currentstate = stateRadio;

       // and the CCA check is good 
       if (currentstate == PRE_TX_STATE) {
         if (TOSH_READ_RADIO_CCA_PIN()) {
           atomic stateRadio = TX_STATE;
           sendPacket();
         }
        // etc...

  here there's no RSSI_VALID flag check because, I guess, the radio it is supposed to be in rxMode for at least 8 symbol periods. Do you agree? 

  thank you



  On 7/3/07, Marco Antonio Lopez Trinidad <marco.lopez at unige.it> wrote:
    Hi Roberto,

    on the radio manual (page 51 of 90), the description of CCA pin says:

    The clear channel assessment signal is based on the measured RSSI value and a
    programmable threshold. The clear channel assessment function is used to 
    implement the CSMA-CA functionality specified in [1]. CCA is valid when the
    receiver has been enabled for at least 8 symbol periods.

    bla, bla...

    Implementing CSMA-CA may easiest be done by using the STXONCCA command strobe, 
    as described in the Radio control state machine section on page 44.
    Transmission will then only start if the channel is clear. The TX_ACTIVE status
    bit (see Table 5) may be used to detect the result of the CCA.

    ciao,
    --marco.

    > > The TOSH_READ_RADIO_CCA_PIN() can be used every time you issue a request
    > > to
    > > dispatch a packet, if the pin is active then you can go...
    >
    > thank you marco, but what do you mean by "if the pin is active"? CCA_PIN 
    > returns the result of the operation (RSSI > CCA), but in order to read the
    > RSSI, the radio, I guess, need 8 symbol periods. So, I think one should
    > control the RSSI_FLAG before that, isn it?
    >
    > On 7/3/07, Aleksandr N. Sadkov <axel at wl.unn.ru> wrote:
    > >
    > > >
    > > >
    > > > On the base of what I understand for the CC2420, 
    > > >
    > > > The TOSH_READ_RADIO_CCA_PIN() can be used every time you issue a request
    > > > to
    > > > dispatch a packet, if the pin is active then you can go...
    > > > 
    > > > The RSSI value indicates if there is activity in the channel in order to
    > > > start
    > > > receiving a packet.
    > >
    > > What about the RSSI value for noise in this case? 
    > >
    > > >
    > > > --marco.
    > >
    > >
    > >
    > > wbr, Sadkov Aleksandr
    > > axel at wl.unn.ru
    > > www.sumkino.com
    > > www.wl.unn.ru
    > >
    > > _______________________________________________
    > > 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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