Question

For each of the instructions below, assume the initial conditions shown for

r3-r5 and the flags.
For each instruction, show the value of any registers that are changed.
If the instruction affects flags, show the value for all flags that are affected.
Initial conditions:
r3 = OxF0E1 D2B3
r4 = 0x1496 3A40
r5 = Ox 47 CE 811E
NZCV = 1010

a) ADCS r4,r3,r4
b) CMP r3,r5
c) TST r4,#OXF
d) MVNS r5,r3
e) ASRS r3, r3, #1

Answer 1

The student's question involves ARM assembly language instructions and their effects on CPU registers and processor flags. Operations such as ADCS, CMP, TST, MVNS, and ASRS are examined, and their potential effects on registers like r3, r4, and r5, as well as the NZCV flags, are described.

Step-by-step explanation:

The student's question is related to ARM assembly language instructions and the effects they have on CPU registers and processor flags. The instructions given (ADCS, CMP, TST, MVNS, ASRS) are typical of ARM processors, and they involve operations like arithmetic addition, comparison, bitwise testing, bitwise negation, and arithmetic shift right. Here is a breakdown of how each instruction affects the registers and flags:

• ADCS r4,r3,r4: This instruction will add the values of r3 and r4 together, with the carry flag, and store the result in r4. It will also update the flags based on the result. The carry flag is set, meaning the addition will include an extra one.
• CMP r3, r5: This instruction compares r3 with r5 by subtracting r5 from r3, updating the NZCV flags based on the result but not storing the result anywhere.
• TST r4, #0XF: This instruction performs a bitwise AND between r4 and 0x0000000F, affecting the NZCV flags based on the result but not changing any register values.
• MVNS r5, r3: This instruction negates (bitwise NOT) the content of r3 and stores the result in r5, also affecting the NZCV flags.
• ASRS r3, r3, #1: This instruction performs an arithmetic shift right by one bit on the value in r3 and stores the result back into r3, affecting the NZCV flags due to the operation.

Note: The actual values that the registers would contain after executing each instruction depend on the initial values of the registers, which the question does not provide.