From 18e5bf9c075982b504ab40b647e90ea29c638524 Mon Sep 17 00:00:00 2001
From: Mathieu Lacage <mathieu.lacage@sophia.inria.fr>
Date: Thu, 15 Nov 2007 14:21:48 +0100
Subject: [PATCH] keep track of the last time a backoff was updated.

---
 src/devices/wifi/dcf-manager.cc | 8 +++++---
 src/devices/wifi/dcf-manager.h  | 2 +-
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/src/devices/wifi/dcf-manager.cc b/src/devices/wifi/dcf-manager.cc
index 65b1c78be..17455f40a 100644
--- a/src/devices/wifi/dcf-manager.cc
+++ b/src/devices/wifi/dcf-manager.cc
@@ -55,10 +55,11 @@ DcfState::UpdateFailedCw (void)
   m_cw = cw;
 }
 void 
-DcfState::UpdateBackoffSlotsNow (uint32_t nSlots)
+DcfState::UpdateBackoffSlotsNow (uint32_t nSlots, Time backoffUpdateBound)
 {
   uint32_t n = std::min (nSlots, m_backoffSlots);
   m_backoffSlots -= n;
+  m_backoffStart = backoffUpdateBound;
 }
 
 void 
@@ -319,7 +320,7 @@ DcfManager::UpdateBackoff (void)
       if (backoffStart <= Simulator::Now ())
         {
           Scalar nSlots = (Simulator::Now () - backoffStart) / m_slotTime;
-          uint32_t nIntSlots = lrint (nSlots.GetDouble ());
+          uint32_t nIntSlots = lrint (nSlots.GetDouble ());          
           /**
            * For each DcfState, calculate how many backoff slots elapsed since
            * the last time its backoff counter was updated. If the number of 
@@ -329,7 +330,8 @@ DcfManager::UpdateBackoff (void)
           if (nIntSlots > state->GetAifsn ())
             {
               MY_DEBUG ("dcf " << k << " dec backoff slots=" << nIntSlots);
-              state->UpdateBackoffSlotsNow (nIntSlots);
+              Time backoffUpdateBound = backoffStart + Scalar (nIntSlots) * m_slotTime;
+              state->UpdateBackoffSlotsNow (nIntSlots, backoffUpdateBound);
             }
         }
     }
diff --git a/src/devices/wifi/dcf-manager.h b/src/devices/wifi/dcf-manager.h
index 1c70519eb..39e9089ea 100644
--- a/src/devices/wifi/dcf-manager.h
+++ b/src/devices/wifi/dcf-manager.h
@@ -29,7 +29,7 @@ private:
   uint32_t GetBackoffSlots (void) const;
   Time GetBackoffStart (void) const;
 
-  void UpdateBackoffSlotsNow (uint32_t nSlots);
+  void UpdateBackoffSlotsNow (uint32_t nSlots, Time backoffUpdateBound);
 
   virtual bool NeedsAccess (void) const = 0;
   virtual void NotifyAccessGranted (void) = 0;