🔬 Lab 3 Memory#

📌 Objectives#

  • Students should be able to write assembly code to access memory using the LDR and STR instructions.

  • Students should be able to find values stored in registers and memory space using the CCS debugging tools.

Note

Always code as if the guy who ends up maintaining your code will be a violent psychopath who knows where you live.

Tip

START EARLY! You only need to write 10 - 15 lines of assembly code, but it may take much longer than you expect. Start early and seek EI if needed!

📜 Synopsis#

In this lab, you will write an Assembly program determining whether given integers are prime or composite. A prime number is a positive integer that is divisible by only 1 and itself. The equivalent C program is provided in Lab03_PrimeMain.c in the Lab03_PrimeNumbers project.

The array of numbers to test is {1, 2, 7, 10, 15, 62, 97, 282, 408, 467, 967, 6687, 25913, 25481, 118061, 0}. The number 0 at the end of the array is to indicate the end of array. The result array should be {-1, 1, 1, -1, -1, -1, 1, -1, -1, 1, 1, -1, 1, -1, 1, x}, where 1 denotes prime, -1 denotes composite, and x denotes don't care.

An integer \(n\) is not divisible by a number \(m\) if \(n/2 < m < n\). For example, 15 is not divisible by any number between 7.5 and 15 (i.e. 15 is not divisible by 8, 9, … , or 14). So, you don’t have to check if 15 is divisible by these numbers. That’s why the following for loop in Lab03_PrimeMain.c only goes checks to see if a number \(n\) is divisible by 2, 3, 4, … , or \(m\) (with \(m = n/2\)) :

for (int i = 2; i <= m; i++)  //  m is  n/2

💻 Procedure#

Setup#

  • Connect the LaunchPad to your computer via the provided USB cable.

  • Open Code Composer Studio (CCS) and select your workspace.

  • Ensure your Project Explorer is open on the left of the CCS screen. Otherwise, select View > Project Explorer.

  • Open the Lab03_PrimeNumbers project by double-clicking it.

Run main.c#

  • Right-click on Lab03_PrimeMain.c in the Lab03_PrimeNumbers project and ensure Exclude from Build IS NOT checked.

  • Right-click on Lab03_Prime.asm in the Lab03_PrimeNumbers project and ensure Exclude from Build IS checked.

  • Open Lab03_PrimeMain.c and carefully read the code.

  • Click the Debug icon on the main toolbar.

  • Click on the Resume icon (F8) followed by the Suspend icon (Alt+F8). The program will stop at while(1);

  • Observe the values of the Res array in the Expressions tab. You may need to click on > next to Res to expand the array into individual variables. Note: If the Res array is not visible on the Expressions tab, click Add new expression and type Res into the text box.

  • Take a screenshot of the contents of Res after execution of the code. Note: The contents of the Res array should match the values shown in the results array in the Synopsis section

  • Press the Terminate icon to leave Debug mode.

Warning

Please take a screenshot of the region of interest and ensure that it is legible. If your instructor has trouble reading it, you might not get full credit.

Attention

You will receive a grade of -10 points if you submit a picture of a computer screen taken by your phone or mobile device.

Complete Lab03_Prime.asm#

Tip

Before you start writing code, carefully read both Lab03_PrimeMain.c and Lab03_Prime.asm and the comments in them.

  • Right-click on Lab03_PrimeMain.c in the Lab03_PrimeNumbers project and ensure Exclude from Build IS checked.

  • Right-click on Lab03_Prime.asm in the Lab03_PrimeNumbers project and ensure Exclude from Build IS NOT checked.

Modulo

For the modulo operation, use the assembly code provided below.

UDIV R8, R0, R6 ; R8 = R0/R6 (n/i)
MUL  R9, R8, R6 ; R9 = int(n/i) * i
CMP  R0, R9     ; n == int(n/i) * i ?,  n is divisible by i if R0 == R9.

Add your code to Lab03_Prime.asm

  • Use Lab03_PrimeMain.c as a reference to complete the assembly code. Please read all the comments before writing any code.

  • It is important to comment your code. You must add a comment to every line for this assignment.

Verify contents of Result array

  • Once your assembly code is complete, click the Debug icon.

  • Click on the Resume icon (F8 or green arrow) followed by the Suspend icon (Alt+F8 or yellow pause icon). The program will stop at Stall B Stall.

  • Search for the contents of Result array using the Memory Browser. You will need to do the following:

    • Type ResAddr into the Memory Browser search bar to show the contents of ResAddr (which is the address to the Result array).

    • Type the address saved in ResAddr into the Memory Browser search bar (e.g. 0x2000000A).

    • Change the encoding style (number format) to 8-bit Signed Int using the drop-down box

You should see something similar to the figure below. If you hover over the numbers in the Memory Browser, you will see the memory address for that specific 8-bit value. Start at first address for the Result array (e.g. 0x2000000A) and verify the contents of the array match the values shown in the results array in the Synopsis section.

../_images/Lab03_PrimeResultMemory.png

Fig. 1 Memory Browser with 8-Bit Signed Int encoding style.#

  • If you select a wrong encoding style as shown below, you will not be able to correctly read the values inside Result.

../_images/Lab03_PrimeResultMemoryBad.png

Fig. 2 Memory Browser with Character encoding style.#

Tip

There are many assembly examples in CCS if you are looking for assembly syntax. For example, take a look at Example04_ArrayAdd for LDR, LDRB, STRB, loops, etc.

Note

ASR is a shift operator, which is the same as >> in C. If you right shift a number by 1, it is the same as dividing by 2. For example, b1000 (8) >> 1 = b0100 (4).

Tip

If you divide 7 by 2, the answer is 3, not 3.5 in C. If you divide 7.0 by 2, the answer is 3.5.

float y = 7/2;   // y is 3.0, integer division (3) followed by type casting w/ float
float y = 7.0/2; // y is 3.5
int y = 7.0/2;   // y is 3, floating division (3.5) followed by type casting w/ int

🚚 Deliverables#

Deliverable 1#

  • [4 pts] Run Lab03_PrimeMain.c in the Lab03_PrimeNumbers project and take a screenshot showing the contents of Res after the execution of the code. You must expand the array to show the individual values in the array.

Deliverable 2#

  • [7.5 pts] Complete Lab03_Prime.asm and add a comment to every line of your code. Push your code to your repository. It is your responsibility to check your files have been successfully pushed to your GitHub repository.

Warning

Your code must be compilable. If your code throws any compile errors, you will get a grade of 0 for Deliverable 2.

Deliverable 3#

  • [4 pts] Provide screenshots showing the addresses of Result and Nums, stored in RAM/ROM (use the Memory Browser and the pointers you created).

Deliverable 4#

  • [4 pts] Provide a screenshot showing the contents of Result, stored in memory after execution of the code (use the Memory Browser and change the format to 8-Bit Signed Int).

  • [-10 pts] Take pictures of your screen with a mobile device or digital camera and submit them on Gradescope. Yes, I am serious…