Worksheet #4 Condition Code Flag and Arithmetic Operations

Transcription

1 Name: Student ID: Date: Name: Student ID: Objectives Worksheet #4 Condition Code Flag and Arithmetic Operations To understand the arithmetic operations of numeric values To comprehend the usage of arithmetic instructions and their effects To understand the interpretation of condition code flags in ARM processor 1. Create a new project, then type and add the following code to the project. AREA PROG4_1, CODE, READONLY LDR R0, =X LDR R1, =Y ADD R2, R0, R1 Program Replace X and Y in the program above with the values as shown in Table Build and Run the program. Then observe and record the results in Table 4.1. The results from ADD instruction 0x456 0x789 0x x xF2169ABC 0xA xE x Table From Program 4.1, replace the ADD instruction with ADDS instruction as follows: ADD R2, R0, R1 ADDS R2, R0, R1 5. Repeat the step 2 and 3 again. Then observe and record the results in Table 4.2. The results from ADD instruction 0x456 0x789 0x x xF2169ABC 0xA xE x Table 4.2

2 What is the range of signed decimal values that can fit in R0 R2 or any 32-bit registers? What is the range of unsigned decimal values that can fit in R0 R2 or any 32-bit registers? If we interpret the result in R2 as unsigned value, does the last two values of X and Y in Table 4.2 (and 4.1) give us correct answers in R2? If NO, what are the correct answers? Modify program 4.1 in order to get correct answers for the last two values of X and Y if we interpret the result in R2 as the addition of two unsigned valued. Given that the result of addition store in R2 (high double word) and R3 (low double word). Hint: use ADC instruction. R0 R1 + R2 R3 6. Create a new project, then type and add the following code to the project. AREA PROG4_2, CODE, READONLY LDR R0, =X LDR R1, =Y SUB R2, R0, R1 Program 4.2

3 7. Replace X and Y in the program above with the values as shown in Table Build and Run the program. Then observe and record the results in Table 4.3. The results from SUB instruction Table From Program 4.2, replace the SUB instruction with SUBS instruction as follows: SUB R2, R0, R1 SUBS R2, R0, R1 10. Repeat the step 7 and 8 again. Then observe and record the results in Table 4.4. The results from SUBS instruction Table 4.4 From Table 4.4, what do the carry flags (C) imply in case of subtraction? C = 1 implies that C = 0 implies that 11. Create a new project, then type and add the following code to the project. AREA PROG4_3, CODE, READONLY R2 R3 LDR R2, =0x LDR R3, =0x R4 R5 LDR R4, =0x2468ABCD LDR R5, =0x SUBS R1, R3, R5 SUB R0, R2, R4 R0 R1 Program 4.3 Program 4.3 shows a method for subtracting one 64-bit integer from another. The first operand is stored in R2 and R3 while the second in R4 and R5. The result of subtraction will store in R0 and R1. Build and Run the program. Then observe the result. Is the result is correct? Why? If the result is incorrect, revise the program.

4 12. Create a new project, then type and add the following code to the project. AREA PROG4_4, CODE, READONLY LDR R0, =Y LDR R1, =X RSB R2, R0, R1 Program Replace X and Y in the program above with the values as shown in Table Build and Run the program. Then observe and record the results in Table 4.5. The results from RSB instruction Table 4.5 Compare the result and condition flags in Table 4.5 with Table 4.3. Are they different? 15. From Program 4.4, replace the RSB instruction with RSBS instruction as follows: RSB R2, R0, R1 RSBS R2, R0, R1 16. Repeat the step 13 and 14 again. Then observe and record the results in Table 4.6.

5 The results from RSBS instruction Table 4.6 Compare the result and condition code flags in Table 4.6 with Table 4.4. Are they different? Write an assembly program that subtracts one 64-bit integer from another as described in Program 4.3 using RSB or RSBC. 17. From the following ARM assembly program, fill the value inside register R0, R1, and R2, and condition flag N, Z, C, and V after executed each instruction. Instructions R0 R1 R2 N Z C V MOV a1, #0x15 MOV a2, #0xFFFFFF00 SUB a3, a1, a2 ADD a1, a3, a1 ADDS a3, a2, a2 MOV a3, #200 MOV a1, #-10 SUBS a2, a3, a3 SBCS a2, a3, a3 RSB a3, a2, a1

6 Instructions R0 R1 R2 N Z C V RSCS a1, a2, a3 ADCS a3, a1, a2 SUBS a3, a1, a2 RSBS a3, a1, a2 ADDS a2, a1, a3 SBCS a1, a2, a3 LDR a1, =0x7FFFFFFF ADDS a2, a1, a1 ** LDR register, =data uses to load data from memory to register. It accepts 32-bit data while MOV register, #data can only accept 8-bit data. However, MOV instruction is faster than LDR instruction. ** 18. Convert the following sentences to ARM assembly program Sentences ARM assembly program Load value 100 to register a1 Load value 150 to register a2 a3 = a1 + a2 a4 = a2 - a1 (and update CC) a1 = a2 + a3 + Carry bit in CPSR Load value 200 to register a3 a2 = a3 - a3 (and update CC) After the execution of the following program is terminated, What are the values inside registers : R0 =. R1 = R2 =. R3 = What are the values inside condition flags : N =.. Z =.. C =.... V =

7 Question 1. Write an assembly program that adds two 64-bit values together as the detail shown below: Hint: