Project 4 Assembly Programming


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Project 4
Assembly Programming

(A) Project Demo [70%]: + Bonus Question (published separately)
You will be graded for correctness of the programs (asm) you have coded. We will be running test
of all your asm codes using Nand2tetris software (Assembler and CPU Emulator).
(B) Project Quiz [30%]: Take Home, Will be announced on Saturday Nov 9th Morning
(Submit on eCampus by: Saturday, Nov 9
, 11:59 PM )
Deliverables & Submission
You need to turn in ONLY the asm files (div.asm, fill.asm, lcd.asm, mod.asm) for all the programs.
We will test with our own test and compare files
Put your full name in the introductory comment present in each ASM code.
Use relevant code comments and indentation in your code.
Zip all the required assembly (asm) files into a compressed file
Submit this zip file on eCampus.
Late Submission Policy: Refer to the Syllabus
Every hardware platform is designed to execute commands in a certain machine language,
expressed using agreed-upon binary codes. Writing programs directly in binary 1, 0 sequence of
code is a possible, yet unnecessary and often error prone. Instead, we can write such programs
using a low-level symbolic language, called assembly, and have them translated into binary code
by a program called an assembler. In this project you will write some low-level assembly
programs, and will be forever thankful for high-level languages like C and Java. (Actually,
assembly programming can be highly rewarding, allowing direct and complete control of the
underlying machine.)
To get a taste of low-level programming in machine language, and to get acquainted with the
Hack computer platform. In the process of working on this project, you will become familiar
with the assembly process – translating from symbolic language to machine-language – and you
will appreciate visually how native binary code executes on the target hardware platform. These
lessons will be learned in the context of writing and testing three low-level programs, as follows.
Description Comments / Tests
Write a program to calculate the
quotient from a division operation.
The values of dividend a and
divisor b are stored in RAM[0]
(R0) and RAM[1] (R1),
respectively. The dividend a is a
non-negative integer, and the
divisor b is a positive integer.
Store the quotient in RAM[2]
(R2). Ignore the remainder.
Example: if you are given two numbers 15 and 4 as dividend
a (R0) and divisor b (R1), then the answer will be 3 stored in
● Write your div.asm program using the Hack assembly
● Use the supplied Hack Assembler (tools) to translate your
div.asm program, producing a div.hack file containing
binary Hack instructions.
● Next, load the supplied div.tst script into the CPU
Emulator (tools). This script loads the div.hack program,
and executes it. Run the script.
● If you get any errors, debug and edit your div.asm
program. Then assemble the program, re-run the div.tst
script, etc.
Note that the div.tst file is nearly complete to establish strong
familiarity with testing methods, but it *may* be missing
‘corner conditions’. Assure yourself of such cases and add as
Implement a program that
calculates the modulo of two given
numbers a and b, which is a%b in
The value of a is stored in
RAM[0] (R0), and the value of b
is stored in RAM[1] (R1). The
value a is non-negative integer and
b is positive integer. The modulo
value is stored in RAM[2] (R2).
Example: If you are given two numbers 18 and 4 stored in
RAM registers, R0 and R1, then the (18 modulo 4) will be 2
stored in R2.
Here, you are given starter tst and cmp files. Complete these
files with additional test cases to the best of your abilities and
test your code against them. Follow similar instructions for
the testing procedure as noted above in the case of div.
Implement a program that
calculates the largest common
divisor (lcd) of two given
non-negative integers, which are
stored in RAM[0] (R0) and
RAM[1] (R1). The lcd is stored in
RAM[2] (R2).
Use Euclidean algorithm here. Here is a link showing you
how Euclidean’s algorithm works to find lcd of two numbers:
Here, you are given starter tst and cmp files. Complete these
files with additional test cases to the best of your abilities and
test your code against them. Follow similar instructions for
the testing procedure as noted above in the case of div.
I/O handling: this program
illustrates low-level handling of
the screen and keyboard devices,
as follows:
The program runs an infinite loop
that listens to the keyboard input.
When a key is pressed (any key),
the program darkens the screen,
i.e. writes “1” in every bit for each
pixel; the screen should remain
fully dark as long as the key is
When no key is pressed, the
program clears the screen, i.e.
writes “0” in every pixel; the
screen should remain fully bright
as long as no key is pressed.
Start by using the supplied assembler to translate your
fill.asm program into a fill.hack file.
Implementation note:
Your program may darken and brighten the screen’s pixels in
any spatial/visual order, as long as pressing a key
continuously for long enough results in a fully dark screen,
and not pressing any key for long enough results in a fully
bright screen.
The simple fill.tst script, which comes with no compare file,
is designed to do two things:
(i) load the fill.hack program, and
(ii) remind you to select ‘no animation’, and then test the
program interactively by pressing and releasing some
keyboard keys.
The fillAutomatic.tst script, along with the compare file
fillAutomatic.cmp, are designed to test the fill program
automatically, as described by the test script documentation.
For completeness of testing, it is recommended to test the fill
program both interactively and automatically.
Write and test the four programs described above. When executed on the supplied CPU
emulator, your programs should generate the results mandated by the specified tests.
The Hack assembly language is described in detail in Chapter 4 .
You will need two tools:
1. The supplied assembler – a program that translates programs written in the Hack
assembly language into binary Hack code. TUTORIAL: PDF
2. The supplied CPU emulator – a program that runs binary Hack code on a simulated Hack
platform. TUTORIAL: PDF
Debugging tip: The Hack language is case-sensitive. A common error occurs when one
writes, say, “@foo” and “@Foo” in different parts of one’s program, thinking that both
labels are treated as the same symbol. In fact, the assembler treats them as two different
symbols. This bug is difficult to detect, so you should be aware of it.
The supplied Hack Assembler can be used in either command mode (from the command shell),
or interactively. The latter mode of operation allows observing the translation process in a visual
and step-wise fashion, as shown below:
The machine language programs produced by the assembler can be tested in two different ways.
First, one can run the resulting .hack program in the supplied CPU emulator. Alternatively, one
can run the same program directly on the Hack hardware, using the supplied hardware simulator
used in projects 1-3. To do so, one can load the Computer.hdl chip (built in project 5) into the
hardware simulator, and then proceed to load the binary code (from the .hack file) into the
computer’s Instruction Memory (also called ROM). Since we will only complete building the
hardware platform and the Computer.hdl chip only in the next project, at this stage we
recommend testing machine-level programs using the supplied CPU emulator.
The supplied CPU Emulator includes a ROM (also called Instruction Memory) representation,
into which the binary code is loaded, and a RAM representation, which holds data. For ease of
use, the emulator enables the user to view the loaded ROM-resident code in either binary mode,
or in symbolic / assembly mode. In fact, the CPU emulator even allows loading symbolic code
written in assembly directly into the ROM, in which case the emulator translates the loaded code
into binary code on the fly. This utility seems to render the supplied assembler unnecessary, but
this is not the case. First, the supplied assembler shows the translation process visually, for
instructive purposes. Second, the assembler generates a persistent binary file. This file can be
executed either on the CPU emulator, as we illustrate below, or directly on the hardware
platform, as we’ll do in the next project.

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