Instruction Set
Loading a word from an unknown alignment
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enter with address in Ra (32 bits) |
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uses Rb, Rc; result in Rd. |
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Note d must be less than c e.g. 0,1 |
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BIC |
Rb,Ra,#3 |
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get word aligned address |
LDMIA |
Rb,{Rd,Rc} |
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get 64 bits containing answer |
AND |
Rb,Ra,#3 |
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correction factor in bytes |
MOVS |
Rb,Rb,LSL#3 |
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...now in bits and test if aligned |
MOVNE |
Rd,Rd,LSR Rb |
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produce bottom of result word |
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(if not aligned) |
RSBNE |
Rb,Rb,#32 |
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get other shift amount |
ORRNE |
Rd,Rd,Rc,LSL Rb; |
combine two halves to get result |
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75
76 Instruction Set 
This chapter describes the THUMB instruction set.
Thumb |
Instruction Set |
77 |
Format Summary
The THUMB instruction set formats are shown in the following figure.
Figure 38. THUMB Instruction Set Formats
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Rd |
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Offset8 |
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Word8 |
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Rb |
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Offset5 |
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SP |
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Rd |
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Word8 |
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SWord7 |
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Rlist |
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Soffset8 |
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Offset11 |
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1 |
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H |
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Offset |
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Move shifted register
Add/subtract
Move/compare/add /subtract immediate
ALU operations
Hi register operations /branch exchange
PC-relative load
Load/store with register offset
Load/store sign-extended byte/halfword
Load/store with immediate offset
Load/store halfword
SP-relative load/store
Load address
Add offset to stack pointer
Push/pop registers
Multiple load/store
Conditional branch
Software Interrupt
Unconditional branch
Long branch with link
78 Instruction Set 