Figure 6-12 Swp Instruction; Swp Instruction - ARM ARM966E-S Technical Reference Manual

Bus Interface Unit
6-16

SWP instruction

The ARM instruction performs an atomic read-modify-write operation. It is
SWP
commonly used with semaphores to guarantee that another process cannot modify a
semaphore when it is being read by the current process.
If the ARM966E-S performs a
always unbuffered to ensure that the core is stalled until the write has occurred on the
AHB. The BIU asserts the HLOCK output to prevent the AHB arbiter from granting a
different master, ensuring that the read-modify-write is atomic.
Figure 6-12 shows a
SWP
CLK
HTRANS
HADDR
HRDATA
HWRITE
HWDATA
HLOCK
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operation to an AHB address location, the access is
SWP
instruction.
IDLE NONSEQ IDLE
A_SWP
A_SWP
NONSEQ IDLE
SWP_D2

Figure 6-12 SWP instruction

ARM DDI 0186A