Contents
Which instructions are conditional instructions?
Conditional instruction (if, then, else)
- if: the condition to be evaluated first.
- then: the expression to be evaluated in case the result of the condition evaluation is true.
- else: the expression to be evaluated in case the result of the condition evaluation is false.
What is a condition code ARM?
In ARM state, you can use a condition code to control the execution of VFP instructions. The instruction is executed conditionally, according to the status flags in the APSR, in exactly the same way as almost all other ARM instructions.
What are the advantages of conditional execution feature in ARM?
You can use conditional execution of ARM instructions to reduce the number of branch instructions in your code. This improves code density. The IT instruction in Thumb achieves a similar improvement. Branch instructions are also expensive in processor cycles.
What are conditional codes?
a set of single bits that indicate specific conditions within a computer. The values of the condition codes are often determined by the outcome of a prior software operation and their principal use is to govern choices between alternative instruction sequences.
What are major features of ARM?
The main features of ARM Processor are mentioned below :
- Multiprocessing Systems –
- Tightly Coupled Memory –
- Memory Management –
- Thumb-2 Technology –
- One cycle execution time –
- Pipelining –
- Large number of registers –
What is conditional execution in ARM?
ARM PROCESSOR FUNDAMENTALS Conditional execution controls whether or not the core will execute an instruction. If they match, then the instruction is executed; otherwise the instruction is ignored. The condition attribute is postfixed to the instruction mnemonic, which is encoded into the instruction.
How can an instruction be executed conditionally in arm?
Almost all ARM instructions can be executed conditionally on the value of the condition flags in the APSR. You can either add a condition code suffix to the instruction or you can conditionally skip over the instruction using a conditional branch instruction.
Are there any conditional instructions in Cortex M?
The answer is that all instructions can be conditional. The Cortex-M architecture supports a variety of condition codes that can be appended to any ARM assembly instruction. If the flags in the APSR match the given condition code, the instruction is executed as normal.
Which is an example of a conditional code in arm?
Here are some examples from the ARM reference manual which illustrates this logic: IT NE ; Next instruction is conditional ADD R0, R0, R1 ; Syntax error: no condition code used in IT block. Here are the conditional codes and their opposite: Let’s try this out with the following example code:
How many instructions can be executed conditionally in thumb state?
Specifically, the Thumb version which allows conditional execution (Thumb-2). Some ARM processor versions support the “IT” instruction that allows up to 4 instructions to be executed conditionally in Thumb state. Reference: http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0552a/BABIJDIC.html