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FIT1047 Introduction to computer systems, networks and security - S1 2025

Assignment 2 – MARIE Programming (v1.3 22/03/2025)

Purpose

This assignment is mainly about programming in the MARIE assembly language. This will allow students to demonstrate their comprehension of the fundamental ways a processor works. In addition, basic knowledge about processes, memory and files is assessed in an in-class test.

The assignment relates to Unit Learning Outcomes 2, 3 and 4.

Your tasks

Part 1: Submit your reflections. See details below.

Part 2: Disassemble and add comments to a MARIE program.

Part 3: Write a MARIE program that can display bitmap numbers.

Part 4: In-class in-person test and interview (week 8 applied session).

Value

25% of your total marks for the unit.

The assignment is marked out of 60 marks.

Word Limit

See individual instructions

Due Date

Part 1–3: 11:55 PM Friday 11 April 2025

Part 4: Interview and test conducted during your official allocated

Applied Session in Week 8

Submission

● Via Moodle Assignment Submission.

● DRAFT submissions are not assessed. Re-check your submission in Moodle.

● Turnitin and MOSS will be used for similarity checking of all submissions. Ignore Turnitin warnings or error messages for .mas files or other non-document files.

● DRAFT upload confirmation email from Turnitin is not a submission. You must click the submit button to accept terms and conditions in Moodle.

● This is an individual assignment (group work is not permitted).

● In this assessment, you must not use generative artificial intelligence (AI) to generate any materials or content in relation to the assessment task.

● You will need to explain and extend your code in an interview. (Part 4)

Assessment Criteria

Part 1 is assessed based on relevance of the submission to the unit.

Part 2 is assessed based on correctness of the code and the labels/comments.

Part 3 is assessed based on correctness of the code, as well as the documentation/comments.

Part 4 is assessed based on the understanding of the code you have written. See instructions for details.

Late Penalties

5% deduction per calendar day or part thereof for up to one week.

Submissions more than 7 calendar days after the due date will receive a mark of zero (0) and no assessment feedback will be provided.

Support Resources

See Moodle Assessment page

Feedback

Feedback will be provided on student work via:

general cohort performance

specific student feedback ten working days post submission

INSTRUCTIONS

This assignment has four parts. Make sure you read the instructions carefully.

For Part 1, collect your reflections from each week’s Ed Lesson and create a single PDF document. You can simply copy/paste your reflections, but please add headings for each week. A template is available on Moodle. Submit the PDF through the Moodle Assignment activity.

For Part 2 and 3, you need to submit files through the Moodle Assignment activity. Each part requires the submission of one or two .mas files inside a .zip file.

You may see the following error message from Turnitin. You can ignore this error message!

Part 4 is an in-class interview and test during your allocated Applied Class in Week 8. Instructions will be available in Moodle and communicated via an announcement post.

Disassembled program:

Input

Add 005

Output

Jump 000

Halt

DEC 10

Note: You need to decode the actual instructions. E.g. for the first memory location, HEX 5000 would not be a valid answer. The contents of all memory that follows the Halt instruction is considered to be data. Therefore, DEC 10 is the correct decoding of location 5 (instead of JnS 00A), and HEX 00A would also be correct. You don’t need to list all the locations containing   zeros starting from address 006 (these will be filled with zeros by the assembler anyway).

Tip: You can verify that your disassembled code is correct by entering it into the MARIE simulator, assembling it and comparing the memory contents to the screenshot you started from.

Task 2: Add labels (5 marks)

Now update the program you decoded in Task 2.1. Remove all hard-coded memory addresses by adding labels to replace all memory locations that are used as addresses in the program instructions. Labels should have meaningful names in the context of what the program does (i.e., not just A, B, C). For the example above, this could result in the following program:

MainLoop, Input

Add Ten

Output

Jump MainLoop

Halt

Ten, DEC 10

Hints: All data used by the code can be interpreted as integer numbers, so it’s probably best to use the Decimal output mode. Run the code and observe the output. Ask yourself how the output relates to the given data. Use the step functionality in the MARIE simulator to understand step by step what the code does. Which parts are subroutines? Which parts are loops? What do the SkipCond instructions do? How are the different data values used?

Task 3: Add comments (7 marks)

Comment the code based on your understanding of what it does. Comments should describe the function of the different parts. E.g., if you identify a subroutine in the code, add a comment at the start of the subroutine that describes what it does, and whether it takes  any arguments.

For this part (Part 2), you need to submit a ZIP file containing a single .mas file containing your final code. If you attempted all three tasks, your .mas file should not contain three copies of the code - only submit the Task 3 code in that case (or only Task 2 if you did not attempt Task 3).

In the simplest form of graphics hardware, we can dedicate part of the RAM to be graphics memory. Each memory cell corresponds to a pixel on screen, and the value in the memory cell encodes the colour of the pixel. That way, we can create arbitrary graphics by simply writing values into the memory.

The MARIE simulator has a feature called Display, which you access from the list of tabs that also shows the output log, RTL log etc:

The display shows the memory from address F00 to address FFF as a 16x16 pixel screen.  The value in the memory locations represents the colour of the pixels. We will only use the   colours black, represented as 0, and white, represented as FFFF. When you start the MARIE simulator and assemble your code, the memory starting from location F00 is (usually) filled with zeroes, which means that the display is black. Let’s now change the contents of the memory using some Store instructions:

Load White

Store 0F80

Store 0F81

Store 0F82

Store 0F83

Halt

White, HEX FFFF

After running this program, the display will look like this:

You can see that the first four pixels in the 9th row have now turned white.

Task 1: Clearing the display (4 marks)

Write a subroutine SubClearDisplay that uses a loop to turn all pixels in the graphics memory white. Remember that the graphics memory ranges from address 0F00 to address 0FFF,  and that white pixels are represented by the value FFFF. Document your subroutine with  comments.

Task 2: Painting a character (10 marks)

The template for this task contains data for bitmaps of the letters “a”-”z”, stored at the label  Font. Each letter consists of 4x8 pixels of data. The first 4 words are the first row of pixels, the next 4 words are the second row, and so on. For example, the letter “a” is represented as

You can see the pattern here, the zeros “paint” the shape of the character “a” . We have highlighted the zeros in bold and red to make the pattern easier to see, but on the real display, the zeros would be black against the white background (FFFF).

Your task is to write a subroutine called SubPaintChar that paints a character into the graphics memory. The start of the subroutine needs to look like this:

PaintCharCharacter, HEX 0

PaintCharDisplay, HEX 0

SubPaintChar, HEX 0

In the PaintCharCharacter argument, we pass the address of the first pixel data in the font for   the character we want to paint. In the PaintCharDisplay argument, we pass the address of the  top-left corner where we want to start painting in the graphics memory. For example, to paint the character “c”, starting from the second pixel in the second row, we could use the following code:

Load FontAddr

Add SIXTYFOUR

Store PaintCharCharacter

Load Display22

Store PaintCharDisplay

JnS SubPaintChar

Halt

Display22, HEX 0F11

SIXTYFOUR, DEC 64

Note that the address 0F11 (label Display22) lies exactly 17 words after the start of the graphics memory. This means we’re skipping the first row (16 words) and the first pixel in the second row (1 word).

Here we use FontAddr, which refers to the first character (“a”), and then add decimal 64 to it, to get the address of the character “c” (each character uses 4x8=32 words of memory, so “c” starts at FontAddr + 64). For the other characters, we would have to add a corresponding offset into the font memory.

In order to paint a character in your subroutine, you can follow this “recipe” :

-    Your subroutine should contain two nested loops.

-     Each character contains 32 pixels, so you need to loop through those 32 pixels, load each one from the font definition and store it into the graphics memory. This is the outer loop of your subroutine.

-    After each set of 4 pixels, you need to start in the next row of the graphics display. This means that if you were currently writing into graphics memory at address X, you now  need to continue writing at address X plus the width of the display minus the width of a character. This is the inner loop of your subroutine.

-    Once you have “copied” all 32 pixels from the font definition into the graphics memory, you can exit the subroutine.

Your subroutine needs to contain sufficient comments to enable someone else (like the person marking your assignment) to understand the purpose of each line of your code.