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Questions and Answers
Which of the following best describes the function of the LDR instruction in ARM assembly language?
Which of the following best describes the function of the LDR instruction in ARM assembly language?
- Performs arithmetic operations on register values.
- Stores data from a register to RAM.
- Loads data from RAM to a register. (correct)
- Moves data from one register to another.
What is the primary purpose of the STR instruction in ARM assembly?
What is the primary purpose of the STR instruction in ARM assembly?
- To store data from a register into memory. (correct)
- To define a string literal within the code.
- To load data from memory into a register.
- To perform a bitwise operation on a register.
The MOV instruction in ARM assembly always requires additional memory access instructions to retrieve data.
The MOV instruction in ARM assembly always requires additional memory access instructions to retrieve data.
False (B)
In ARM assembly, what are the four fields typically found in a line of code, separated by spaces or tabs?
In ARM assembly, what are the four fields typically found in a line of code, separated by spaces or tabs?
In the ARM assembly instruction LDR R0, [R1, #4]!, the ! indicates a ______ addressing mode.
In the ARM assembly instruction LDR R0, [R1, #4]!, the ! indicates a ______ addressing mode.
Match each addressing mode with its description in ARM assembly:
Match each addressing mode with its description in ARM assembly:
Which addressing mode involves the data being directly embedded within the instruction itself?
Which addressing mode involves the data being directly embedded within the instruction itself?
In indexed addressing, the actual data is stored within the instruction itself.
In indexed addressing, the actual data is stored within the instruction itself.
Explain the role of a register in indexed addressing.
Explain the role of a register in indexed addressing.
In PC-relative addressing, the ______ register is used as a pointer.
In PC-relative addressing, the ______ register is used as a pointer.
Which addressing mode is most suitable when the data's location is relative to the current instruction's address?
Which addressing mode is most suitable when the data's location is relative to the current instruction's address?
Writing an initial value into a memory location and transferring data from one memory location to another are capabilities microcontrollers do not possess.
Writing an initial value into a memory location and transferring data from one memory location to another are capabilities microcontrollers do not possess.
What is the purpose of comments in assembly language code?
What is the purpose of comments in assembly language code?
In the example assembly code, .global main declares the main label as ______.
In the example assembly code, .global main declares the main label as ______.
Referring to the optional modifiers for reading from/writing to memory; what does the H modifier signify?
Referring to the optional modifiers for reading from/writing to memory; what does the H modifier signify?
With the SB optional modifier, values are zero-padded to 32 bits on load.
With the SB optional modifier, values are zero-padded to 32 bits on load.
What does PC stand for in the context of PC-relative addressing mode?
What does PC stand for in the context of PC-relative addressing mode?
The instruction MOV R0, #0 will assign the value ______ to register R0.
The instruction MOV R0, #0 will assign the value ______ to register R0.
Which instruction is used to indefinitely loop the program execution in the provided sample ASSEMBLY program?
Which instruction is used to indefinitely loop the program execution in the provided sample ASSEMBLY program?
In general, Assembly language is considered a high-level programming language.
In general, Assembly language is considered a high-level programming language.
Flashcards
What does LDR do?
What does LDR do?
LDR is used to load data from RAM into a register
What does STR do?
What does STR do?
STR is used to store data from a register into RAM.
What does MOV do?
What does MOV do?
MOV is used to move or copy data within the processor, without needing memory access.
What is immediate addressing?
What is immediate addressing?
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What is indexed addressing?
What is indexed addressing?
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What is PC-relative addressing?
What is PC-relative addressing?
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Study Notes
- These study notes cover accessing memories in Cortex-M3 and ARM assembly language.
- The objective is to provide an overview of ARM instructions for reading from and writing to memory.
Assembly Language Syntax
- Assembly language syntax has four fields: label, opcode, operands, and comments.
- Fields are separated by spaces or tabs.
- The label field is a unique name for each label.
- The opcode field is the command to execute by the processor.
- The operands field can be 0 to 4 values, separated by commas.
- The comments field includes programmer explanations of the software.
- Example:
Func: MOV R0, #100 ; this sets R0 to 100
General Format of Assembly Program
- The data memory section typically ranges from
0x20000000-0x20004FFF. - The program memory section typically ranges from
0x08000000-0x0801FFFF. - Key directives include
.section .datafor data,.section .textfor code,.syntax unified, and.global main.
Reading and Writing to Memory
- Microcontrollers write an initial value into a memory location (e.g.,
0xAAtoMEM[0x40]). - Microcontrollers transfer data from one memory location to another (e.g., from
MEM[0x30]toMEM[0x40]). - Load data from RAM to a register using the
LDRinstruction.- Example:
ldr r1, =0x20000000(special form),ldr r0, [r1](r0 =[0x20000000]).
- Example:
- Store data from a register to RAM using the
STRinstruction.- Example:
str r0, [r1]// [0x20000000] = r0
- Example:
- Use the
MOVinstruction to get data from within the processor, without additional memory access instructions.- Example:
mov r0, #0// r0 = 0, mov r1, r0// r1 = r0
- Example:
Addressing Modes
- Addressing mode specifies the memory location to write and read data.
- There are three main types: Immediate Addressing, Indexed Addressing, and PC-Relative Addressing.
Immediate Addressing
- The data is contained in the instruction.
- Example:
MOV R0, #100; R0 = 100, immediate addressing, which loads the value100directly into registerR0.
- Example:
Indexed Addressing
- The data is in memory, and a register contains a pointer to the data.
- Example:
LDR R0, [R1]; R0 = word pointed to by R1.
- Example:
- Subtypes include with constant value, with register value, pre-increment, and post-increment.
PC-Relative Addressing
- This is an indexed addressing mode using the PC (program counter) as the pointer.
- Example:
LDR R1, =Count;R1points to variableCount.LDR R0, [R1] ; R0 = Count; pointed to by R1
- Example:
Optional Modifiers
- {type} indicates the data type, such as 32-bit word, unsigned 8-bit byte, signed 8-bit byte, unsigned 16-bit halfword, signed 16-bit halfword, and 64-bit data.
- B: Unsigned 8-bit byte (0 to 255); zero-padded to 32 bits.
- SB: Signed 8-bit byte (-128 to +127); sign-extended to 32 bits.
- H: Unsigned 16-bit halfword (0 to 65535); zero-padded to 32 bits.
- SH: Signed 16-bit halfword (-32768 to +32767); sign-extended to 32 bits.
- D: 64-bit data utilizes two registers.
Activities
- Use a simulator for assembly code (e.g., CPUlator) to write assembly programs.
- Write a program to output a sequence to LEDs, reading values from data memory.
- Write a program to swap the least and most significant 16-bits of a value (e.g.,
0xCCFF3300) and display it on LEDs.
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