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Questions and Answers
What is unique about the way ARM processors encode immediate values?
How many basic data processing instructions do ARM processors have?
What is the purpose of the LSL instruction in the ADD instruction?
What is the result of the instruction 'ADD r0, r2, r3, LSL #4'?
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What is the binary representation of the hex value 0xD7?
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What is the result of rotating the binary number 01101101 right by 0 bits?
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What is the purpose of the ROR instruction?
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How many operands can the ADD instruction work with?
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What is the main function of the ADD instruction?
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What is the typical design of the ARM processor architecture?
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Study Notes
ARM Immediate Value Encoding
- ARM instruction set encodes immediate values in an unusual way, using only 12 bits of instruction space to represent a useful set of 32-bit constants.
Machine Code and ARM Processors
- Machine code is a binary representation of simple instructions that computer processors run on.
- All ARM processors have 16 basic data processing instructions.
- Each data processing instruction can work with several combinations of operands.
Data Processing Instructions
- Examples of data processing instructions include ADD instructions:
- ADD r0, r2, r3 ; r0 = r2 + r3
- ADD r0, r2, r3, LSL #4 ; r0 = r2 + (r3 shifted left by 4 bits)
Instruction Encoding
- ARM instruction encoding uses 32 bits, with 12 bits allocated for immediate values.
- The immediate value is encoded in a way that allows for a useful set of 32-bit constants to be represented.
Example Instruction Encoding
- Example instruction encoding: 0x000000D7
- Breakdown of the encoding:
- 0x0 (most significant bits)
- 0xD7 (least significant bits, rotated right by 0 bits to get 215)
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Description
Learn about the unique way ARM instructions encode immediate values, using only 12 bits of instruction space to represent a useful set of 32-bit constants.
