Lab 1b. ARM Assembly and Keil Debugging Solution

Preparation

You will need a LaunchPad and a laptop/computer with Keil uVision5 installed. Download the Lab 1b starter project from Canvas.

Starter project    Lab 1b

Purpose

The purpose of this lab is for you to become familiar with using the debugger in Keil. Additionally, you will gain exposure to ARM assembly programming in the form of arithmetic operations.

Introduction

In this lab you will learn some of the features that are available within Keil for debugging your programs. In the latter portion of the lab you will finish a program by writing three functions. The correctness of each function can be tested by holding down a specific button combination. Each test will either blink a specified LED if correct, or blink the red LED if it failed. A correct example test will run when no buttons are pressed.

Procedure

    1. Let X, Y, and Z be three numbers as shown below. In the project provided for this lab write assembly instructions to perform the operations listed in the table below. After each operation record the Result (R) and the states of condition flags N, Z, V, and C in the PSR register. You will need to set breakpoints and use the debugger to observe these values. Figure 1 shows how this can be done in Keil.

X = 0x0000 0008, Operation

Y = 0xFFFF FFFD, Result (R)

Z = 0x7FFF FFFF Condition Codes
N    Z    V    C


R=X+Y


R=X–X


R=X+Z


R=Y–Z


R=Y+Z




















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EE/CPE 287 Lab 1b
Lab Time_______________________    Name_____________________________























Figure 1: Debugging in Keil

All of the debugging commands can be found under the Debug menu in addition to on the toolbar. Breakpoints can be added and removed by selecting Insert/Remove Breakpoints. You can start or stop the debugger by going to Start/Stop Debug Session under the same menu. Once in the debugger you can use Step to execute one line at a time or Run to execute the program until it hits a breakpoint. Stop will halt a running program and can be useful when trying to determine why your program never reaches a desired breakpoint.

The code for this part and part 2 can be inserted after the “debug” function label in main.s. Fill out the table and demonstrate using the debugger to the TA. Explain to the TA what the N, Z, C, and V flags stand for.




Signature_______________________________    Date_________


    2. Next you will use the Memory Window to study the various forms of the LDR instruction. The Memory Window can only be accessed by going to View Memory Window and choosing a window. Memory windows are only available while using the debugger. In the memory window, put in the address 0x20000000 (beginning of RAM space) as shown in Figure 2. The data found there was set by some initialization function. Fill in the table below with the values loaded into R6 when using each of the various forms of the LDR instruction.











Figure 2: Memory Window





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EE/CPE 287 Lab 1b
Lab Time_______________________




First run:
MOV R7, #0x20000000


Then:
LDR R6, [R7]
R6 =

LDRH R6, [R7]
R6 =

LDRB R6, [R7]
R6 =

LDRSH R6, [R7]
R6 =

LDRSB R6,[R7]
R6 =
Name_____________________________




First run:
MOV R7, #0x20000000
ADD R7, #2

    • Must use add because 0x20000002 cannot be represented as

    • an immediate value

Then:
LDR R6, [R7]
R6 =

LDRH R6, [R7]
R6 =

LDRB R6, [R7]
R6 =

LDRSH R6, [R7]
R6 =

LDRSB R6,[R7]
R6 =




The code for this part can be inserted in the same location as the code for part 1. Show the completed table to the TA. Be sure you are able to explain to the TA what each variation does and why you got the results you did. You should be able to relate your results to the information displayed in the memory window.


Signature_______________________________    Date_________


    3. In the file main.s fill in the code for “Part3_Function”. Your code will implement the arithmetic operation Z = (A<<2) | (B&15). This code is tested by holding down SW1. A successful test of your code will result in the Blue LED blinking. Incorrect code will result in the Red LED blinking. Be sure to read the comments above the function! Show your correct code to the TA.





Signature_______________________________    Date_________








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EE/CPE 287 Lab 1b
Lab Time_______________________    Name_____________________________


    4. Next fill in the code for “Part4_Function”. Your code will implement the arithmetic operation Z = ((A+B)+(A-B)) | (A<<B). This code is tested by holding down SW2. A successful test of your code will result in the Green LED blinking. Incorrect code will result in the Red LED blinking. Be sure to read the comments above the function! Show your correct code to the TA.






Signature_______________________________    Date_________



    5. Lastly, fill in the code for “Part5_Function”. Your code will implement the arithmetic operation Z = X + Y where X = ((A*8)|(B*4)|(C*2)) and Y = ((B xor 2)|(C xor 4). This code is tested by holding down both SW1 and SW2. A successful test of your code will result in the Blue and Green LEDs simultaneously blinking. Incorrect code will result in the Red LED blinking. Be sure to read the comments above the function! Show your correct code to the TA.






Signature_______________________________    Date_________



































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EE/CPE 287 Lab 1b