Building Our Digital World: Computer Systems and Architecture
COMP1860
Activity Sheet 2.3
This worksheet contains a combination of formative activities (which contribute towards your learning) and summative activities (which you will complete and submit to be assessed as part of your portfolio).
Every exercise marked with a red border is a summative exercise and must be submitted as part of your portfolio. You should use PebblePad to submit portfolio activities. In addition, you may be required to submit other activities — the module teaching staff will provide instructions.
Activities marked by (*) are advanced, and may take some time to complete.
Expectations:
1. Timeliness You should complete all of the activities in the order provided and submit your portfolio evidence on PebblePad before the completion date (Friday, 21/02/2025, at 17:00).
2. Presentation You should present all of your work clearly and concisely following any additional guidance provided by the module staff in the module handbook.
3. Integrity You are responsible that the evidence you submit as part of your portfolio evidence is entirely your own work. You can find out more about academic integrity on the Skill@library website. All work you submit for assessment is subject to the academic integrity policy.
Feedback: Feedback on formative activities will be provided via Lab classes and tutorials. Feedback on evidence submitted as part of the portfolio will be available on PebblePad.
Support opportunities: Support with the activity sheet is available in the Lab classes and tutorials. Individual support is available via the online booking system.
Expected time for completion: 2-3 hours.
Expected complete date: Friday, 21/02/2025, at 17:00
Coursework summary
We have discussed the stack machine paradigm and discussed the semantics of the Hack Virtual Machine language. You will now write programmes for the Hack Virtual Machine. You have already written Hack assembly code to perform. these tasks in Weeks 1 and 2 of Semester 2 (Activity Sheets 2.1 and 2.2), but you will now be using a different paradigm. In addition to the lecture slides on the Hack Virtual Machine, useful references for this activity sheet are [1, Chap. 7 and 8] and the corresponding YouTube videos by the authors.
Learning outcomes
On completion of this activity sheet, you will have:
1. examined the design of a stack machine;
2. implemented simple programmes utilising the stack machine paradigm;
3. designed and implemented simple programmes for the Hack Virtual Machine; and
4. utilised a simulator of the Hack Virtual Machine to test and debug programmes.
Instructions
Please submit your .vm files to the Activity Sheet 2.3 assessment on Gradescope. To complete this activity sheet, your solutions to the portfolio questions will need to pass at least 75% of the tests. When this happens, Gradescope will return an 8-character string for you to add as evidence in the PebblePad workbook for this activity sheet.
1. In the file EvaluateExpression.vm, write a programme for the Hack Virtual Machine that evaluates the expres- sion z = 17+x-3y, where x and y are the values initially stored in argument[0] and argument[1], respectively. The code must leave the final result z at the bottom of the stack and must not modify the values initially stored in argument[0] and argument[1].
2. In the file Xor.vm, write a programme for the Hack Virtual Machine that computes z = x ⊕ y, where ⊕ denotes the element-wise xor (exclusive or) logical operator, and x and y are the values initially stored in argument[0] and argument[1]. The code must leave the final result z at the bottom of the stack and store it in argument[2]. The values initially stored in argument[0] and argument[1] must not be modified.
3. In the file AbsoluteValue.vm, write a programme for the Hack Virtual Machine that computes z = |x|, where x is the value initially stored in argument[0]. The code must store the result z in argument[1] and must set argument[2] to 1 if x is negative and to 0 otherwise. The memory location argument[3] must be set to 1 if the absolute value of the input cannot be computed, and to 0 otherwise. The value initially stored in argument[0] must not be modified. Hint: The approach you used in your solution to Question 3 in Activity Sheet 2.1 can be adapted quite directly to the stack machine paradigm.
4. In the file Square.vm, write a programme for the Hack Virtual Machine that computes y = x
2
, where x is the values initially stored in argument[0]. The code must leave the final result y at the bottom of the stack and must not modify the value initially stored in argument[0]. Hint: The approach you used in your solution to Question 1 in Activity Sheet 2.2 can be adapted quite directly to the stack machine paradigm.
5. (*) In the file AddWithOverflowCheck.vm, write a programme for the Hack virtual machine that computes the sum z = x+y, where x and y are the values initially stored in argument[0] and argument[1], respectively. The code must store the result z in argument[2] and set argument[3] to 1 if the sum overflows, and to 0 otherwise. The values initially stored in argument[0] and argument[1] must not be modified. Hint: The approach you used in your solution to Question 4 in Activity Sheet 2.1 can be adapted quite directly to the stack machine paradigm.
References
[1] Noam Nisan and Shimon Schocken. The Elements of Computing Systems: Building a Modern Computer from First Principles. The MIT Press, Cambridge, MA, USA, second edition, 2005. The book is available to view and down-load at https://ebookcentral.proquest.com/lib/leeds/detail.action?docID=6630880. Additional material is available at https://mitpress.mit.edu/books/elements-computing-systems.