School of Computing: assessment brief
   Module title
 Computer Processors
  Module code
 COMP1212
  Assignment title
 August Resit
  Assignment type and description
 In-course assessment. Requires design implementation and testing of code written in HDL and assembly lan- guage
  Rationale
 Provides an opportunity to write HDL and assembly code including understanding the implementation of branching and functions.
  Word limit and guidance
 This coursework should take less than 25 hours to com- plete.
  Weighting
 100%
  Submission dead- line
 5pm 9/8/24
  Submission method
 Gradescope
  Feedback provision
 Feedback will be provided through Gradescope
  Learning outcomes assessed
 Describe the basic building blocks of a computer in de- tail and explain how they are composed to construct computing machinery.
Apply appropriate tools to develop, simulate and test logic circuits (CAD).
Explain how high level programming constructs, such as ’if’ statements and ’for’ loops, are implemented at a machine level
  Module lead
 Andy Bulpitt
  Other Staff contact
 Noleen K ̈ohler
             1

1. Assignment guidance
There are two sections to this resit assessment. Section I requires implementation of
HDL programs and Section II requires the implementation of assembly language. 2. Assessment tasks
SECTION I
Your task is to design and implement a circuit in hdl which takes two 2-bit numbers (A, B) and (C, D) as input and produces a 3-bit output (E, F, G).
The final circuit has 6 inputs in total (f1, f0, A, B, C, D) and 3 outputs (E, F, G). The function of the circuit is determined by the two inputs f1 and f0.
The truth tables below define the operation of the circuit for each combination of f1 and f0.
ABCDFG ABCDFG 000011 000000 000110 000100 001001 001000 001100 001100 010011 010000 010110 010101 011001 011000 011100 011101 100011 100000 100110 100100 101001 101010 101100 101110 110011 110000 110110 110101 111001 111010 111100 111111
                                    Table 1: When f1, f0 = (1, 1) FZero
Table 2: When (f1, f0) = (1, 0) FOne
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  ABCDFG ABCDEFG 000000 0000000 000101 0001001 001010 0010010 001111 0011011 010001 0100001 010101 0101010 011011 0110011 011111 0111100 100010 1000010 100111 1001011 101010 1010100 101111 1011101 110011 1100011 110111 1101100 111011 1110101 111111 1111110
Table 3: When (f1, f0) = (0, 1) FTwo Table 4: When (f1, f0) = (0, 0) FThree
(a) For each of the truth tables above, implement a logic circuit in HDL that will perform the function specified by the truth table. You should create one circuit for each truth table and test it produces the required output for that truth table. The circuit for each truth table should be named FZero, FOne, FTwo, FThree corresponding to the names of the truth tables given above and must have corresponding filenames FZero.hdl, FOne.hdl, FTwo.hdl, FThree.hdl.
Each circuit must have four inputs named A,B,C and D. Chips FZero, FOne and FTwo will have two outputs (F,G). Chip FThree will have three outputs named E,F and G.
You must only use the built-in AND, NAND, OR, NOR, NOT, Mux, XOR or DMux chips.
The test files provided (.tst and .cmp) can be used to test each output of a chip. For example FZero1.tst tests the F output of the chip FZero.hdl and FZero2.tst tests the G output of FZero.hdl.
[9 marks]
(b) Combine all four circuits into one circuit which takes all six inputs and three
                                  3

outputs and test it to ensure it produces the correct output depending on the value of the inputs f1 and f0. Call the chip FALL. You can test this chip using FALL.tst but may wish to create further tests before submission. The value of output E is undefined (can be either 0 or 1) unless (f1, f0) = (0, 0)
You must only use the built-in AND, NAND, OR, NOR, NOT, Mux, XOR or DMux chips.
[4 marks]
(c) Stretch Activity
When performing computational operations it is often useful to be able to exe- cute a sequence of operations, each one using the output of the previous step as an input to the next step. For example to OR 3 values X OR Y OR Z you might first calculate X OR Y and then on the next step apply OR Z to the previous output (X OR Y ).
For this task adapt the circuit FALL so that it can combine a sequence of operations defined by different values for f1 and f0 at each step, by enabling the outputs Ft and Gt of step t to be used (feedback) as the inputs for the next operation Ct+1 and Dt+1 for step t + 1. You should also add a further input (Load) to the chip which when Load = 1 will enable you to load new inputs to Ct andDt andwhensetto0setsCt+1 =Ft andDt+1 =Gt. TheLoadinput will allow you to manually set the values of C and D at the start and during the sequence if required.
Call this chip FSEQ. You can test this chip using FSEQ.tst but may wish to create further tests before submission.
You must only use the built-in AND, NAND, OR, NOR, NOT, Mux, DMux, XOR or DFF chips.
[Total for Section I 20 marks]
SECTION II
The Feistel cipher is a symmetric block cipher encryption framework which is the basis of many modern day encryption algorithms. In this coursework you will implement a Feistel cipher system as a software implementation in both a high level language and Hack Assembly.
In a Feistel cipher the plaintext, P, to be encrypted is split into two equal size parts L0 and R0 such that P = L0R0. A function F is applied to one half of the plaintext, combined with a key, and the result is XOR’d with the other half of the plaintext.
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[7 marks]

Feistel ciphers often employ multiple rounds of this scheme. In general the scheme works as follows, for all i = 0,...,n,
Li+1 = Ri
Ri+1 =Li ⊕F(Ri,Ki)
To decrypt an encrypted message using this cipher we can apply the same procedure inreverse. Fori=n,n−1,...,0,
Ri = Li+1
Li =Ri+1 ⊕F(Li+1,Ki)
For this coursework we are interested in the 16-bit Feistel cipher which uses 4 rounds. The function F (A, B) = A ⊕ ¬B.
The keys are derived from a single 8-bit key K0 such that,
K0 = b7b6b5b4b3b2b1b0 K1 = b6b5b4b3b2b1b0b7 K2 = b5b4b3b2b1b0b7b6 K3 = b4b3b2b1b0b7b6b5
(a) Write a program (XOR.asm) in HACK assembly that implements an XOR func- tion between two 16-bit values stored in RAM[3] and RAM[4] and stores the result in RAM[5].
[6 marks]
(b) Write a program (Rotate.asm) in HACK assembly that implements an algorithm to rotate the bits of a 16-bit number left (Least Significant bit (LSb) to Most Significant bit (MSb)). The original number should be stored in RAM[3] the number of times to rotate the bits should be in RAM[4] and the result stored in RAM[5], i.e. 1010111100000000 rotated left 3 times would be 0111100000000101 where the MSb is used to replace the LSb.
[12 marks]
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(c) Write a program (FeistelEncryption.asm) in HACK assembly, that implements the described Feistel encryption system. The initial key, K0, will be stored in RAM[1], and the 16-bit plaintext will be stored in RAM[2]. The result of the encryption should be stored in RAM[0].
[12 marks]
[Total for Section II 30 marks]
3. General guidance and study support
Tools required to simulate the hardware and CPU are provided on Minerva under Learning resources: Software.
Please ensure the files you upload work with the test files provided and use the filenames provided in this sheet. Do not alter the format of the lines of these test files in any way. The spacing in each line needs to be preserved You are of course welcome to build your own test files in the same format or add to these files.
Ensure the files you upload pass the submission tests provided on Gradescope. These are not necessarily the same tests as those that will be used to grade your submission.
4. Assessment criteria and marking process
This coursework will be marked using Gradescope. Feedback will be provided through
Gradescope and example solutions discussed in class.
Marks are awarded for passing the automated tests on the submitted programs de- tailed below.
5. Presentation and referencing
Submitted code should provide suitable comments where possible.
6. Submission requirements
Links to submit your work can be found on Minerva under Assessment and feed-
back/Submit my work.
For section I submit only your hdl files, uploaded individually. Ensure you use only the filenames provided in this specification sheet. The names must match the specification exactly, including the use of upper and lower case characters i.e. FZero.hdl is valid however, fzero.hdl or FZero.HDL are not valid.
For section II submit only your asm files.
7. Academic misconduct and plagiarism
Academic integrity means engaging in good academic practice. This involves essential academic skills, such as keeping track of where you find ideas and information and referencing these accurately in your work.
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By submitting this assignment you are confirming that the work is a true expression of your own work and ideas and that you have given credit to others where their work has contributed to yours.
8. Assessment/marking criteria grid Section I
No marks will be awarded for tests which fail or use of chips other than those listed.
• Part (a) There is one test to check the complete truth table for each output of the chips [9 marks].
• Part (b) There are four tests to check the complete truth table of the FALL chip [4 marks].
• Part (c) will be evaluated by testing it on three sequences of functions of various lengths [7 marks].
[Total for Section I 20 marks]
Section II
No marks will be awarded for tests which fail
• Part a) is graded using 3 tests, each worth 2 marks. [max 6 marks] • Part b) is graded using 4 tests, each worth 3 marks. [max 12 marks] • Part c) is graded using 4 tests, each worth 3 marks [max 12 marks]
[Total for Section II 30 marks]
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