ARM ARM7TDMI User Manual download pdf (Page 37)

Page 33

Usage and Examples:

The SWP instruction exchanges a word between a register and memory. This

instruction is intended to support semaphore manipulation by completing the transfers

as a single, atomic operation.

ADR R1, semaphore ;semaphore address

MOV R0, #1

SWP R0, R0, [R1] ;make swap

CMPS R0, #0 ;test result

4.36 SWPB – Swap Byte

Syntax:

SWPB{<cond>} <Rd>, <Rm>, [<Rn>]

RTL:

if(cond)

temp  [Rn]

[Rn]  Rm

Rd  temp

Flags updated:

None

Encoding:

31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

cond 0 0 0 1 0 1 0 0 Rn Rd SBZ 1 0 0 1 Rm

Usage and Examples:

The SWPB instruction exchanges a single byte between a register and memory. This

instruction is intended to support semaphore manipulation by completing the transfers

as a single, atomic operation.

ADR R1, semaphore ;semaphore address

MOV R0, #1

SWPB R0, R0, [R1] ;make swap

TST R0, #0xFF ;test result

1 2 ... 32 33 34 35 36 37 38 39 40 41 42 43

No comments

ARM ARM7TDMI User Manual Page 37