Function Number	Function Name	Arguments
-	Switch Context	Nil

Switch Context

    Get the pid of the current process from System Status Table;
    
    Push the BP register of the current process to the top of it's kernel stack. 
    /* The ExpL application does not push the Base Pointer register (BP). See ExpL calling conventions. 
    Hence it is saved to the stop of the Kernel Stack */

    Save the SP%512, PTBR and PTLR to the Kernel SP, PTBR and PTLR fields of the 
    Process Table entry of the current process;  
    
    if (PAGING_STATUS in the System Status Table is not 0) /* Paging is ongoing */
	    If the paging process is blocked     /* the paging process is executing a disk operation */
	    	Choose Idle Process for scheduling.
	    else
	    	Choose the Swapper Daemon to be scheduled.
    else
    {
          Find the next non swapped process to schedule using the Round Robin scheduling technique, 
          excluding the Swapper Daemon;
	        /* Check the SWAP_FLAG in the process table */
                If no process (that is not swapped out) is in  READY or CREATED state, select the Idle process;
    }
    
    Set the PTBR and PTLR registers to the corresponding values in the process table entry
    of the new process;
    
    Set the new PID in the System Status Table;
    
    if (the new Process is in CREATED state){ 		/* The process has just been forked from a parent process */

          Set SP to the value of UserSP field in the Process table entry of the new process;
	  Set BP to the value stored at the beginning of the kernel stack.	
	  /* BP value of the process is saved to the beginning of the kernel stack by Fork() system call at process creation. */

    	  Set the state of the new process as (RUNNING, - );

	  Set the MODE_FLAG in the process table entry 0.
          Use ireturn statement to transfer control back to user mode;
    }
    
    Set the state of the new process as (RUNNING, - );
    
    Read the KPTR field and the UArea Page number from the Process table entry of the
    new process;

    Set SP to UArea_Page * 512 + KPTR;
    
    Restore the BP register of the new process from the top of it's kernel stack.

    return;

Called by all blocking functions and the Timer interrupt handler.