This file logs the changes on the Communication Stack for Mica Motes developed
at USC/ISI and UCLA. It includes a physical layer and S-MAC.

* Changes after version 1.1

  1) Added link quality measurement. A new interface LinkState is provide.

  2) Some internal changes are made to S-MAC packet formats to minimize the
     added bytes for link quality measurement.
     
  3) apps/SMACTest/ now includes the test for link state measurement.
  
  4) Added optional time-stamping on outgoing packets for simple time sync.

* Changes after version 1.1-alpha.

  1) Fixed a bug in platform/mica2/ClockSMAC. It makes S-MAC do not work
     well on Mica2 when using timer/counter1.
 
  2) Fixed a bug in platform/mica2/PhyConst.h. It mistakenly set radio
     listen time to be 38.4kbps, which is actually 19.2kbps, since we get
     data from radio after its Machester decoding. This bug causes S-MAC to
     double its carrier sense time. Sometimes a sender sends out even after a
     receiver goes to sleep. This bug is Mica2 specific.

  3) Some robustness improvement in handling neighbors' schedule
     changes.

  4) Some performance improvement in mica2/RadioControlM.nc.
                                                                                
  5) Provides connections with PowerManagement to put CPU into idle mode
     when radio is in sleep.
   
  6) Fixed various small bugs.
  
* On 5/8/2003, version 1.1-alpha released. Changes after v1.0 includes:

  1. New features:
  
   1) Works on Mica2 platform (with Chipcon CC1000 radio).
   
   2) Compatibility support to Berkeley's radio stack that comes from the
      official TinyOS release.
      
   3) Improved neighbor list maintaining. If a neighbor is silent for long
      time, it will be removed from my neighbor list.
      
  2. Bug fixes:
  
   1) Removed a few race conditions that can occur in both MAC layer and
      the physical layer.
      
   2) Fixed potential timestamp error.
   
   3) Various improvement on robustness.

* On 2/8/2003, version 1.0 released. Changes after version v0.1 includes:

  1. New features:

   1) This version is ported to nesC environment.
    
   2) Adaptive listen. If a node overhears a transmission from its neighbors,
      it will wake up at the end of the transmission and listen for a short
      time. During this adaptive listen time, nodes can start sending data.
      Latency can be greatly reduced and throughput can be increased. If there
      is no activity after the adaptive listen time, the nodes will go back to
      sleep again.
 
   3) Fully active mode. User can configure S-MAC at compile time to
      completely disable the sleep cycles in S-MAC. In this mode, no SYNC
      packets are sent. Nodes keep in idle state when there is no data
      transmission. It is similar with IEEE 802.11 but with overhearing
      avoidance and message passing.
	   
   4) Periodic search for new nodes. A node will periodically keep listen for 
      the entire synchronization period (about 10s now). This allows two nodes
      on completely different schedules to find each other and synchronize
      together. The frequency of the neighbor search depends on whether a node
      has any neighbor or not.
	   
   5) Schedule changes. Suppose a node has no neighbor and follows its own 
      schedule. If later it finds a neighbor with a different schedule, it
      will immediately switch to the new schedule.


  2. Bug Fixes:
    
   1) Problem: If a node receives a broadcast packet at the start-up phase
      before it choose a schedule, it goes into sleep that won't be waked up,
      since there is no schedule timer now.
 
      Fix: Each node chooses a tentative schedule as soon as it starts. But
      it does not broadcast this schedule in the first listen period. If it
      receives a new schedule from another node, it will switch to the new
      one immediately.
 
   2) Problem: Occassionally a node can receive a SYNC packet before all
      components are correctly initialized, especially the clock. Sometimes
      the clock time is only 2 ms when the first SYNC packet is received. 
      However, the transmission time of a SYNC packet is about 10ms. This
      will casue synchronization errors, since the new node thinks it follows
      and existing schedule, but its setting of the schedule is actually
      different.
 
      Fix: Check the clock time when receive each SYNC packet. Make sure the
      clock is correctly started. Otherwise don't use the SYNC packet.
 
   3) Problem: The encoding table in CODEC_MANCHESTER (and CODEC_4B_6B) makes
      the "make install.x mica" fail. This is  due to the limitation of the
      'munge_srec' program, which requires the TOS_LOCAL_ADDRESS (defined in
      MAIN.c) to be in a certain line in main.srec. However, if you declare
      a large global variable (like the 16-byte encoding table) in a file 
      whose name is before MAIN.c, the variable is put before 
      TOS_LOCAL_ADDRESS, and will move TOS_LOCAL_ADDRESS to the second line.
      For example the first letter in CODEC_xxxxx is 'C', which is before 
      the 'M' in MAIN.c. Note this problem only occurs in the pre-nesC
      environment.
      
      Fix: Moved the encoding table to the program memory (flash), instead of
      using RAM. So the "make install.x mica" works now.
 
   4) Problem: During the initialization of the radio in RADIO_CONTROL, the
      initial value of SLAVE_PIN is not correctly set. It may cause problem
      when logger is also used, which also uses SLAVE_PIN.
	   
      Fix: Set the correct initial value of the SLAVE_PIN.
 
* Initial version (v0.1) released on Oct 2, 2002.