Mips Technologies R4000 - Examples Using LL and SC

Chapter 11
290 MIPS R4000 Microprocessor User's Manual
Examples Using LL and SC
Figure 11-18 shows how to implement test-and-set using LL and SC
instructions.
Figure 11-18 Test-and-Set using LL and SC
Load semaphore
Unlocked?
(=0?)
Try locking
semaphore
Successful?
(r3=0?)
Unlock semaphore
Execute critical section
(Access shared data)
No
Yes
No
Yes
Loop: LL r2,(r1)
ORI r3,r2,1
BEQ r3,r2,Loop
NOP
SC r3,(r1)
BEQ r3,0,Loop
NOP
SW r2,(r1)
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