[Tinyos-help] about CC2420

[Tsung-Han Lin]

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* <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 – 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 – 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>
>     [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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