CMPSC 200: Dynamo Dispatcher

Date
12 October 2023	Assigned
20 October 2023	Due, end of lab
Status

Learning objectives

• Describe the various functions of the stack and the link register
• Enumerate the call stack for a given set of functions using "Last In, First Out" principles
• Deploy bit shifting as a technique to qualify numeric data
• Use the stack and link register to create dynamic, multi-function programs

Introduction

Branching out, stacking up, and other meaningless phraseology

But, very meaningful Assembly instructions.

Adding it up

Complete this work in adder/program.S.

This exercise replicates our class discussion of the basic stack frame using the following Python addition routine as a basis including a couple of new instructions: BL (branch and link), and BX (branch and execute):

def add(a: int, b: int) -> int:
	c = a + b
	return c

s = add(2, 3)
print(s)

Dynamo Dispatcher

Complete this work in dynamo/program.S.

Our automated station can sense really big space rocks. Like, sufficiently big. In this case that means ones measuring 20 -bits. On each rock signal we encounter that is _20` bits or greater_, we should send out a dynamo to have a look and possibly take some samples so that we can characterize the type and quality of the rocks. (Don't worry: that work is up next.)

However, it's inefficient to do all of this in a long string of instructions. We've got to use what we've learned about the link register (LR) and stack to make this process as smooth as possible.

An example outcome should look like:

(966081) DYNAMO RELEASED!
(753047) DYNAMO RELEASED!
(537691) DYNAMO RELEASED!
(686535) DYNAMO RELEASED!
(843909) DYNAMO RELEASED!
...

Lab: The Sifter

Once we get the rocks, we have to classify them. In our current operation, we collect LUNAR and MARTIAN rocks; then, we sort them into HI and LOW quality. Here're the rules:

Number start (base 16)	Type
00	LUNAR
55	MARTIAN

Number end (base 16)	Quality
FF	HIGH
00	LOW

Hints:

• what are these numbers' decimal equivalents?
• how can we get only the first 2 bytes and last 2 bytes alone?

Note: The portion of our format string 0x%08x indicates that we want to print an 8-digit hexadecimal number.

Assignment "Hacks"

See the Suggestion below to challenge yourself to implement a Hack. As always, you are allowed to develop your own Hack to satisfy this stretch goal. Place the code for the Hack inline with the code in the corresponding file.

In order to recieve credit for the Hack, you must fill out the hack.md file located in the docs folder.

dynamo

Negative values denote very dangerous space junk. We have a blaster to demolish it, but it needs some work. However, we're really only concerned about negative values above 20 bits. Anything else will just bounce off our station's force field.

Note: WORDs function a bit different than BYTES here; negative values will automatically appear as the correct sign.

Replace the signals portion of the .data section with the following:

.data
    signals:        .word       -966081, 475877, 219889, 275073, 753047 
                    .word       507159, 284406, 537691, 38249, -53059
                    .word       181407, 336722, 345502, 166471, -686535
                    .word       452779, 465214, 843909, 286891, 979596
                    .word       370365, 527254, 355151, 273454, -981076
                    .word       904705, 416301, 786009, 760676, 877459
                    .word       91279, 346450, 579616, 740219, 102706
                    .word       728970, 459071, -893083, 70417, 131406
                    .word       188263, -833592, 393345, 96850, 969028
                    .word       583019, 188486, 93105, 830644, -990678
                    .word       820370, 175851, 438405, 727792, 30969
                    .word       718193, 172907, 15193, 475440, 732513
                    .word       -938307, 816167, 103268, 336742, 367860
                    .word       437173, 765356, 941571, 353088, 743371
                    .word       302967, 423311, 318643, 923403, 320974
                    .word       355959, 166521, 771393, 382652, 163116
                    .word       689999, -828204, 61875, 115982, 49647
                    .word       891553, 491925, 94807, 177088, 973945
                    .word       8695, 987054, 656653, 359910, 235998
                    .word       427535, 516345, 426889, -983363, 544308

Implement the blaster by replacing the signals array in program.S with the above and print that we've blasted the junk using a similar format to our dynamo's dispatch message.

Add the following to the .data section of dispatch.s:

    blasted:    .asciz      "(%d) JUNK BLASTED!\n"

sifter

Sometimes, as the saying (and reality) goes, sometimes junk gets lodged in a perfectly good space rock. Here, these scraps are denoted by negative numbers. However, sometimes, they contain technology that we might want to salvage -- especially if the most significant bits are 33. If we encounter a negative-signed sample, and it meets our criteria, we need to print the format string:

    salvaged:     .asciz      "0x%08x\tSALVAGED."

Add the above to the .data section of the sifter.S file.

To add our negative numbers, replace the numbers entry in .data with:

    numbers:    .word   255, 1426063615, 855638271, 0, 1140850943
                .word   -255, -1426063615, -855638271, 0, -1140850943 

Note: WORDs function a bit different than BYTES here; negative values will automatically appear as the correct sign.

New files

For any Hack, you may choose to create a new file to do this; if you do, make sure you add the new file name to the CMakeLists.txt file in the add_executable directive:

add_executable(${PROJECT_NAME}
    program.S
    sifter.S
	your_file_here.S
)

Make it your own

You are free to develop your own "Hack" for this assignment. However, you'll need to be sure to justify the value of your hack clearly!

Changes to files in .vscode

Based on your system setup (refer to your hello-blinky assignment), you will need switch out the .vscode folder in each exercise with the last working copy.

See our wiki's entry on "Configuring Assignments" for more inforamtion.