Initial Exercise
----------------

Below is an exercise to get you going. This will not be formally marked. 
Please note, however, that it has been chosen in such a way that developed
code will come in handy for completing your assembly language project.

Below is the program shown on one of the lecture slides (it prints "Hello
world!"). Copy and paste it into a separate file, such as "ex.x68" (note
that the program must have extension x68). Start the Easy68k software,
and load the file. Under the "project" tab, choose "Assemble Source". If
everything was fine, click "Execute" on the popup window. Click the "run"
button in the simulator window to run the program, and observe the output
that should have appeared.

Now make the following changes: First, change the program so that it uses a
subroutine for writing a character (refer to lecture slide "Simple
subroutines" to see how this is done).  Then change the loop for writing the
characters into a subroutine called "print".  Note that subroutines are
located after the main program (which terminates with move.b #9,d0 and trap
#15) but before the data statements (the line with dc.b).  You should now
have two subroutines called "print" and "output", and "output" is called from
within "print".  Assemble and run the program, and check that it works. 


Start     org       $1000

          lea       str,a0     * points to string
loop      move.b    (a0)+,d1   * next char - start of loop
          beq       next
          move.b    #6,d0      * output it
          trap      #15
          bra       loop       * and continue
next                           * end of loop
          move.b    #9,d0      * exit the main program
          trap      #15

str       dc.b      13,10,'Hello world!',0
          end       Start

You will be able to use the developed code for the first assignment.