Memory Addressing in Assembly Language

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Questions and Answers

Which instruction is used to load the value of A into register R1?

ADD R1, #5

STR R1, ANS

LDR R1, A (correct)

LDR R5, =ANS

What is the purpose of using the pseudo-instruction LDR R3, =C?

To add the value of C to the output register.

To store the final result to the memory location pointed by C.

To substitute C's value literally in register R3. (correct)

To load the address of C into register R3.

How is the final result stored in the memory location indicated by ANS?

By using the instruction STR R0, [R5]. (correct)

By adding the result to the address of ANS.

By issuing a PC-Relative STR instruction.

By loading ANS into register R0.

What corrective action is taken because ARMv7E-M does not support PC-Relative STR?

Substituting the instruction with two separate instructions. Signup and view all the answers

What is the significance of the instruction ADD R1, #5?

It updates R1 with the value of A plus 5. Signup and view all the answers

What does the BL instruction do?

Branches to a label and stores the address of the next instruction in the Link Register (LR). Signup and view all the answers

Which register is commonly associated with the PC (Program Counter) when using BL and BLX instructions?

R14 Signup and view all the answers

How does the BX instruction operate?

It branches to the address indicated by a register. Signup and view all the answers

What distinguishes the BLX instruction from the BL instruction?

BLX branches to a register, while BL branches to a label. Signup and view all the answers

When would you typically use the BL instruction?

When calling a subroutine and needing to return to the next instruction. Signup and view all the answers

What does the ADD instruction do when executed as 'ADD R0, R1, R2'?

Stores the sum of R1 and R2 in R0 Signup and view all the answers

What happens when the Rd operand is omitted in an ADD instruction?

The destination register defaults to Rn Signup and view all the answers

In the instruction 'MUL R0, R1, R2', what is the expected behavior?

R0 will store the product of R1 and R2 Signup and view all the answers

What is the purpose of the MLA instruction in ARM assembly language?

To multiply two numbers and add a third Signup and view all the answers

What does the MLA instruction do when executed as 'MLA R0, R4, R5, R6'?

Stores the sum of R4 times R5 and R6 in R0 Signup and view all the answers

How does the MUL instruction handle signed and unsigned operands?

The signedness of inputs is ignored for the result Signup and view all the answers

How do the long versions of multiplication instructions in ARM assembly differ from their short versions?

They yield 64-bit products. Signup and view all the answers

Which instruction is used to perform a division in ARM assembly language?

SDIV Signup and view all the answers

If the MUL instruction results in a product larger than 32 bits, what happens to R0?

R0 will store the low-order 32 bits of the product Signup and view all the answers

What type of result do CMP and CMN instructions mainly provide?

They update condition code flags without performing arithmetic. Signup and view all the answers

What is the effect of the ADDS instruction compared to the standard ADD instruction?

It updates the NZCV flags based on the result Signup and view all the answers

What is the result of the following instruction: MLS R0, R4, R5, R6?

R0 gets R6 minus the product of R4 and R5. Signup and view all the answers

Which register is affected if the destination register is omitted in the SUB instruction?

Rn will store the result Signup and view all the answers

What does the prefix 'S' in ARM assembly instructions typically signify?

The instruction affects condition flags. Signup and view all the answers

In ARM assembly, what does the UDIV instruction do?

Performs unsigned division without affecting flags. Signup and view all the answers

What will the CMP instruction return if Rn is greater than Op2?

Sets the C flag. Signup and view all the answers

What is the effect of the TST instruction on the Zero flag?

Sets Z to 1 if the least significant bit of R3 is 0 Signup and view all the answers

Which instruction is utilized to check if the value of R2 equals 5?

TEQ R2, #5 Signup and view all the answers

What does the BIC instruction perform on the register Rn?

Rn = Rn & (~Op2) Signup and view all the answers

What is the purpose of the ORN instruction in ARM assembly?

To set bits in a register Signup and view all the answers

In which scenario is the stack used in ARM architecture?

For storing temporary data in Last-In-First-Out order Signup and view all the answers

What does the statement '~R1' represent when R1 = 0x0000FFFF?

0xFFFF0000 Signup and view all the answers

Which of the following statements best describes an Empty stack in ARM?

SP points to the next free location on the stack Signup and view all the answers

What is the primary use of masking instructions like BIC and ORN?

To clear or set bits in configuration registers Signup and view all the answers

Study Notes

Memory Addressing and Operations

Use of assembly language for memory addressing often utilizes pseudo-instructions for convenience, such as .EQU.
Essential operations can be executed with a sequence of instructions that load values, perform arithmetic, and store results in memory.
Example operation to compute ANS involves loading values from addresses A and B, updating them with constants 5 and 10, summing results, and storing in ANS using multiple instructions to navigate ARM's memory handling quirks.

ARMv7E-M Arithmetic Instructions

Addition and Subtraction:
- ADD and SUB instructions follow a specific format, with the destination register (Rd) being optional.
- Operations affect the NZCV flags, which may be useful for subsequent conditional branches.
Multiplication (MUL) and Multiply with Accumulate (MLA):
- MUL computes the product of two registers and only returns the lower 32-bits to the destination register.
- MLA allows for an additional value to be added to the lower 32-bits of the product.
Divisions utilize SDIV and UDIV instructions, performing 32-bit signed or unsigned integer divisions.

Comparison Instructions

CMP and CMN are used to compare registers; CMP performs subtraction whereas CMN adds.
These instructions update the NZCV flags but do not affect the actual arithmetic result, serving primarily for conditional logic.

Branch Instructions

Branch with Link (BL):
- Used for calling functions, saving the return address in the Link Register (LR).
Branch Indirect (BLX and BX):
- BLX branches to the address specified in a register while saving a return address in LR, whereas BX performs a jump to a pointer stored in a register without saving a return address.

Test and Masking Instructions

TST and TEQ:
- TST performs a bitwise AND to check specific bits, affecting the Zero (Z) flag, while TEQ uses EXCLUSIVE OR to determine equality against a specific pattern.
Bitwise Operations (BIC & ORN):
- BIC clears specific bits in a register, and ORN sets certain bits by performing a bitwise OR with the inversions of the corresponding bits in another register.

Stack and Subroutines

Stacks enable efficient memory management using a Last-In-First-Out (LIFO) structure, controlled by the Stack Pointer (SP).
ARM architecture supports multiple stack implementations, categorized by characteristics such as "Empty vs Full" and "Ascending vs Descending".

Assembly Language Format

Explicit assembly language formats define how operations are structured with specific operands and optional conditions, impacting the readability and maintenance of the code.

These principles and instructions form the foundational understanding of using ARM assembly language for efficient programming and system-level operations.

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Description

This quiz focuses on memory addressing concepts in assembly language programming, particularly the use of labels and instructions like LDR. It includes practical examples and applications for better understanding of address manipulation and data loading. Test your knowledge of assembly and address calculations!