[Tinyos-help] CCA Check in application layer.

[David Moss]

If you want to check the channel *before* sending a packet, you can sample
the CCA pin directly.  This GeneralIO is provided by HplCC2420PinsC.

The code you're looking at here actually sends a packet, if the channel is
immediately found to be clear.  If you're not doing so already, you must
also acquire the SPI bus resource before sending commands over SPI. 

-David



-----Original Message-----
From: Hui Kang [mailto:hukang at ic.sunysb.edu] 
Sent: Thursday, July 17, 2008 10:26 AM
To: David Moss
Cc: tinyos-help at millennium.berkeley.edu
Subject: CCA Check in application layer.

Dear All:
In my tinyos-2.x application, I would like to check the channel before 
sending a packet. By copying the following code from CC2420TransmitP.nc, 
I found the congest is always set as TRUE even I have only one mote turn 
on. Could anyone help to solve this problem or any other smarter way to 
check CCA? Thanks.

uint8_t status;
bool congestion = TRUE;
     
atomic{
            call CSN.clr();

        status = call STXONCCA.strobe();
        if ( !( status & CC2420_STATUS_TX_ACTIVE ) ) {
            status = call SNOP.strobe();
          if ( status & CC2420_STATUS_TX_ACTIVE ) {
              congestion = FALSE;
          }
        }
        call CSN.set();
}

- Hui