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wifi: (partial fix for #2477) Avoid assert when transmit cancels a reception

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It is possible for the DCF to be out of sync with the state of the
PHY and to try to transmit a Block Ack when the PHY is receiving.  This
may occur in certain A-MPDU situations.  The assert can be safely removed;
it is for further study whether the scheduled block ack event should be
cancelled to avoid the situation from arising.
This commit is contained in:
Tom Henderson
2016-09-27 10:57:11 -07:00
parent 03e3bf3c05
commit dc8e78e8f7
1 changed files with 21 additions and 7 deletions
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28
src/wifi/model/dcf-manager.cc
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@@ -808,13 +808,27 @@ DcfManager::NotifyTxStartNow (Time duration)
NS_LOG_FUNCTION (this << duration);
if (m_rxing)
{
//this may be caused only if PHY has started to receive a packet
//inside SIFS, so, we check that lastRxStart was maximum a SIFS ago
NS_ASSERT (Simulator::Now () - m_lastRxStart <= m_sifs);
m_lastRxEnd = Simulator::Now ();
m_lastRxDuration = m_lastRxEnd - m_lastRxStart;
m_lastRxReceivedOk = true;
m_rxing = false;
if (Simulator::Now () - m_lastRxStart <= m_sifs)
{
//this may be caused if PHY has started to receive a packet
//inside SIFS, so, we check that lastRxStart was within a SIFS ago
m_lastRxEnd = Simulator::Now ();
m_lastRxDuration = m_lastRxEnd - m_lastRxStart;
m_lastRxReceivedOk = true;
m_rxing = false;
}
else
{
// Bug 2477: It is possible for the DCF to fall out of
// sync with the PHY state if there are problems
// receiving A-MPDUs. PHY will cancel the reception
// and start to transmit
NS_LOG_DEBUG ("Phy is transmitting despite DCF being in receive state");
m_lastRxEnd = Simulator::Now ();
m_lastRxDuration = m_lastRxEnd - m_lastRxStart;
m_lastRxReceivedOk = false;
m_rxing = false;
}
}
MY_DEBUG ("tx start for " << duration);
UpdateBackoff ();