9.17. Data swap

A data swap is similar to a back-to-back load and store instruction. The data is read from external memory in the second cycle and the contents of the register are written to the external memory in the third cycle (which is merged with the first Execute cycle of the next instruction).

The data swapped can be a byte or word quantity.

The swap operation might be aborted in either the read or the write cycle. An aborted swap operation does not affect the destination register.

Note

Data swap instructions are not available in Thumb state.

The LOCK output of the ARM7EJ-S processor is driven HIGH for both read and write cycles, to indicate to the memory system that it is an atomic operation.

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