Notes on the scheduler in sched.c:
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  
    'sched.c' provides an very simplistic multi-threading scheduler.
     See the example, function 'sched(...)', in the same file for its
     API usage.
  
     Until an exhaustive testing can be done, the implementation cannot
     qualify as that of production quality. It works with the example
     in 'sched.c', it may or may not work in other cases.
  
  
  Limitations:
  ~~~~~~~~~~~~
  
    - There are NO primitives for thread synchronization (locking,
      notify etc).
  
    - Only the GPRs and FPRs context is saved during a thread context
      switch. Other registers on the PowerPC processor (60x, 7xx, 7xxx
      etc) are NOT saved.
  
    - The scheduler is NOT transparent to the user. The user
      applications must invoke thread_yield() to allow other threads to
      scheduler.
  
    - There are NO priorities, and the scheduling policy is round-robin
      based.
  
    - There are NO capabilities to collect thread CPU usage, scheduler
      stats, thread status etc.
  
    - The semantics are somewhat based on those of pthreads, but NOT
      the same.
  
    - Only seven threads are allowed. These can be easily increased by
      changing "#define MAX_THREADS" depending on the available memory.
  
    - The stack size of each thread is 8KBytes. This can be easily
      increased depending on the requirement and the available memory,
      by increasing "#define STK_SIZE".
  
    - Only one master/parent thread is allowed, and it cannot be
      stopped or deleted. Any given thread is NOT allowed to stop or
      delete itself.
  
    - There NOT enough safety checks as are probably in the other
      threads implementations.
  
    - There is no parent-child relationship between threads. Only one
      thread may thread_join, preferably the master/parent thread.
  
  (C) 2003 Arun Dharankar <ADharankar@ATTBI.Com>