Starting PennSim in Codio

1)   Opening up the codio X-server:

a.   Along the top menu, click on the blue “play” icon next to “PennSim Window”

b.   If things work, you’ll get a blank black window, this window is called an “Xserver”

i. It can display any “graphical” output of your codio virtual machine

c.    If you see an error # 502.  Contact the professor right away J Don’t attempt to solve this on your own.

2)   Opening up the codio Terminal Window:

a.    On the left hand side of the screen, you will see what’s called the “ File Tree”

i. This is a listing of all the files on your virtual codio computer

b.   Click on the small computer icon; I’ve circled it on the image below:

c.   This will bring up a Linux Terminal Window, where you can manually type in commands to your computer.

d.   Type in (DO NOT COPY & PASTE THIS – type it in manually) the following command to start the LC4 Simulator (PennSim):

java -jar PennSim.jar &

(DO NOT COPY & PASTE THIS – type it in manually)

i. this command uses Java to start our PennSim program

e.    In the “Xserver” window, PennSim (the java app) will open up:

i.   click on the “Preview http… .” tab to see PennSim:

Running Multiply.ASM in PennSim

1)   From the “ File Tree” click on the file: multiply.asm

a.    Examine the contents of the file, notice it is the multiply algorithm from lecture

2)   From the File Tree, click on the file: multiply_script.txt

a.   This file shows all of the commands that must be entered into PennSim to assemble and load the file, examine it line by line

3)   Return back to the “PennSim” window you opened in the last section

a.    In PennSim’s “Controls” section, type in:

script multiply_script .txt

Then press enter:

4)   Press the “Step” button to run the program line by line.  Carefully examine the register file, the program counter, and the state of the machine as you run it line by line!

Learn to use PennSim:

1)   PennSim has a lot of features, we’ve made a video of how to use it and posted it on canvas under : Files->Resources->Tutorials-> PennSimTutorial_in_5minutes.wmv

a. Watch this video before continuing on with the HW

b. Experiment with multiply.asm since its loaded into your PennSim

2)   There is a proper manual for PennSim; it is handy to review.  It is also on canvas under: Files->Resources->Tutorials-> PennSimStartGuide.zip

Assigned Problems (to be done individually, NOT group work):

--Make certain you’ve setup codio and learned PennSim before attempting these problems!

1) WHILE LOOPS IN ASSEMBLY

The pseudo-code below describes the mathematical operation known as a factorial.  When  the algorithm below is completed, the variable B will contain A!  For the given positive value of A, the factorial is defined as 5 x 4 x 3 x 2 x 1 = 120.

Here is the pseudo-code for the factorial algorithm:

A = 5 ;  // example to do 5!

B = A ;  // B=A! when while loop completes

while (A > 1) {

A = A - 1 ;

B = B * A ;

}

Implement the given algorithm using LC4-Assembly.  Use R0 to hold variable A, and R1 to   hold variable B.  In your codio “File Tree” you’ll see a file I created for you: factorial.asm.  Open the factorial.asm file on codio and implement the factorial          algorithm above within it.  Test it using the other file I’ve provided for you: factorial_script.txt.  You may hard code A to have the value 5, but when we        grade your assignment, we will try out different #s to ensure your algorithm is working.  So be certain to run your program in PennSim and make certain it is working for different        values of A.

In your program and in your script file be certain to set a breakpoint labeled “END.”  (see     multiply.asm for an example of this).  This will ensure you program ends, instead of               requiring an infinite loop to stop execution.  Be certain to comment your code (but not over comment), to help us understand the flow of your program as we grade.

POINTS WILL BE DEDUCTED IF YOUR CODE IS NOT COMMENTED!

For this problem you will edit and change the 2 files: factorial.asm and factorial_script.asm

2) SUBROUTINES IN ASSEMBLY

For this problem, you’ll convert your factorial program from problem #1 into a subroutine and call it using JSR.

File setup: After you’ve completed problem #1, copy the file: factorial.asm file in the codio “File Tree” by right-clicking on the file, clicking “copy” and then right clicking once      again in the file tree and pressing “paste.”  Give it the name: factorial_sub.asm.  Next, copy and paste the file: factorial_script.txt.  Give it the name:                       factorial_sub_script.txt.   Next, you’ll need to open the new file:                           factorial_sub_script.txt – to ensure it assembles and loads “factorial_sub.asm” instead of    “factorial.asm”

What to do for this problem:

Add the label : SUB_FACTORIAL to the top of your factorial program.  Remove any “CONST”  instructions you may have that would set the variable A (register R0).  We want “A” to be an argument to your subroutine.  Replace the END label with a RET statement, as we wish B to be the return value for your function.

Above your subroutine code, implement the following code to call your subroutine:

MAIN

A = 6 ;

B = sub_factorial (A) ;

// your sub_factorial subroutine goes here

END

After you return from the subroutine, make certain to “jump” over your subroutine to a     new END label, so that your subroutine isn’t executed twice!  Make certain to set END as a breakpoint in your script file.

Next, add an “If/else” statement to the start of your subroutine to ensure A is a positive # and is <= the largest number your assembly can work with. If A is < 0 or > the largest         number your algorithm can work with, set B = -1 and return from the subroutine without attempting to find the factorial.

POINTS WILL BE DEDUCTED IF YOUR CODE IS NOT COMMENTED!

POINTS WILL ALSO BE DEDUCTED IF YOU DON’T CALL THE SUBROUTINE USING A JSR and RETURN FROM IT USING AN RET!

For this problem you will have created 2 files: factorial_sub.asm and factorial_sub_script.asm

3) WORKING WITH DATA MEMORY IN ASSEMBLY

For this problem, you will have to review the example of working with data memory in lecture, as well as the “sum_numbers.asm” example in the PennSimStartGuide Manual discussed at the start of this assignment.

File setup: After you’ve completed problem #2, copy the file: factorial_sub.asm and paste it with the new name: dmem_fact.asm.  Then copy:                                                       factorial_sub_script.txt and paste it with the new name:                                         dmem_fact_script.txt.  Next, update dmem_fact_script.txt to ensure            assembles and loads “dmem_fact_script” instead of “factorial_sub.asm”

What to do for this problem:

Recall the “ .FILL” directives mentioned in lecture and also in the sum_numbers.asm              example from the PennSimStartGuide.  Use the .FILL directive to populate 5 rows of data    memory starting address x4020 with the numbers: 6, 5, 8, 10, -5.  Write a short assembly    program that will load each of the 5 rows of data memory that you’ve populated and call    the subroutine you’ve created in problem #2 on each of those rows.  After the factorial       subroutine is run on each row, you should then store the #’s factorial back to data memory overwriting the original #.  As an example of how the first row of data memory should look after your program completes, address x4020, should have the number #720.

POINTS WILL BE DEDUCTED IF YOUR CODE IS NOT COMMENTED!

For this part you should generate the 2 files: dmem_fact.asm and dmem_fact_script.txt

e.c. (5 points): In addition to the program above, create a new program in dmem_fact_ec.asm, that allows your subroutine: SUB_FACTORIAL, to take in as its only argument a data memory address (instead of a value). The new SUB_FACTORIAL should then load the value from data memory, specified by the argument, find its factorial, and store the result back in data memory (instead of returning a value). Update your code from problem #3 to call this subroutine properly.