460 LAB #6: Timer for MTX

          460 LAB Assignment #6: Timer for MTX
              DUE : to be announced

0. BACKGROUND:  NOTES on Interrupts and Timer
                
1. Download files from samples/LAB5.timer/ 

      t.c     : YOUR LAB5 .c file but add display driver vid.c and timer
                                          interrupt handler.
      ts.s    : assembly file for this assignment

      timer.c : timer interrupt handler in C
                (as of now, it prints a message every second)
                MODIFY thandler() for this assignment.

2. Implement these timer functions:

   (a). At each second : display current time HH:MM:SS at the lower right 
                         corner. Read my video display driver vid.c code for 
                         how.
   (b). When a proc is scheduled to run, set its PROC.time to an alloted run 
        time, e.g. 5 seconds. Decrement running's run time in Umode only!  
        When a proc's run time expires, switch process.

        NOTE:   do NOT switch process while it's in Kmode!!! 
        REASON: our MTX kernel is NOT a multi-processor kernel. 

   (c). Every 5 seconds: turn off FD if it is on;   (write 0x0C to 0x3F2)
                         turn on  FD if it is off;  (write 0x1C to 0x3F2)

   (d). From Umode, add a command, sleep, which ask for a time t to sleep.
        Syscall to MTX kernel to sleep for t seconds. The process becomes 
        READY to run again when its sleep time expires.