Hi everyone,
When is transmission timestamp considered invalid for a packet? AFAIK, the
only place to invalidate a packet being transmitted is in
CC2420TransmitP$CaptureSFD$captured() as the following code shows:
* /* this is the SFD for received messages */
** if ( !m_receiving && sfdHigh == FALSE ) {
** sfdHigh = TRUE;
** call CaptureSFD.captureFallingEdge();
** // safe the SFD pin status for later use
** sfd_state = call SFD.get();
** call CC2420Receive.sfd( time32 );
** m_receiving = TRUE;
** m_prev_time = time;
** if ( call SFD.get() ) {
** // wait for the next interrupt before moving on
** return;
** }
** // if SFD.get() = 0, then an other interrupt happened since we
** // reconfigured CaptureSFD! Fall through
** }
**
** if ( sfdHigh == TRUE ) {
** sfdHigh = FALSE;
** call CaptureSFD.captureRisingEdge();
** m_receiving = FALSE;
** /* if sfd_state is 1, then we fell through, but at the time of
** * saving the time stamp the SFD was still high. Thus, the timestamp
** * is valid.
** * if the sfd_state is 0, then either we fell through and SFD
** * was low while we safed the time stamp, or we didn't fall through.
** * Thus, we check for the time between the two interrupts.
** * FIXME: Why 10 tics? Seams like some magic number...
** */
** if ((sfd_state == 0) && (time - m_prev_time < 10) ) {
** call CC2420Receive.sfd_dropped();
** if (m_msg)
** call PacketTimeStamp.clear(m_msg);
** }
** break;
** }
** }*
Can someone please help me understand what is going here, especially the
condition to regard a tx timestamp as invalid? Your help will be highly
appreciated.
-Xiaohui Liu
TelosB
TinyOS 2.1.2
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