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ARM Assembly Bit Manipulations Lab

Learn bit shifting in ARM assembly with ASR, LSL, LSR, ROR, RRX. Understand how to isolate and set bits with essential instructions.

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ARM Assembly Bit Manipulations Lab

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  1. Objective The objective of this lab is to introduce the students to bit manipulations using the ARM assembly instruction set. ENSE 352 Lab 4

  2. Bit Shifting • ASR, LSL, LSR, ROR, and RRX • arithmetic shift right • logical shift left • logical shift right • rotate right • rotate right with extend Flags affected N, Z, R

  3. Examples Bit Shifting MOV R0,#1 LSL R0, R0, #3 0 0 0 0 0 0 0 1 0 0 0 0 1 0 0 0

  4. Isolating Bits • Very important for embedded programming. • Often referred to as masking. • Affect only the bit you are interested in. • Utilize the AND and ORR instructions. Ex. Want to determine the state of bit 1 in R0. AND R2, R0, #0x2 Result X X X X X X X X R0 0 0 0 0 0 0 1 0 This bit is isolated and All other bits cleared. R2 0 0 0 0 0 0 X 0

  5. Isolating Bits • Setting a bit without affecting the other bits • Use the ORR instruction. Ex. We want to set bit 1 in R0. ORR R0, R0, #0x2 Result X X X X X X X X R0 0 0 0 0 0 0 1 0 This bit is set to one now. R0 X X X X X X 1 X

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