A serializing instruction is one that stalls due to activity in the VFP11 pipelines without the presence of a register or resource hazard. In general, an access to a VFP11 control or status register is a serializing instruction.

The serializing instructions are FMRX and FMXR, including the FMSTAT instruction. Serializing instructions stall the VFP11 coprocessor in the Issue stage and the ARM processor in the Execute 2 stage until:

An FMRX or FMSTAT instruction stalls until all previous floating-point operations have completed, and the data to be written by the VFP11 coprocessor is valid. For example, until a compare operation updates the FPSCR register condition codes in the Writeback stage of the compare.

An FMXR instruction stalls until all previous floating-point operations are past the point of being affected by the instruction. For example, writing to the FPSCR register stalls until the point when changing the control bits cannot affect any operation currently executing or awaiting execution. A write to the FPEXC, FPINST, or FPINST2 register stalls until the pipeline is completely clear.

Uses of serializing instructions include:

While no instruction can change the contents of the FPSID register, you can access the FPSID register with FMRX or FMXR as a general-purpose serializing operation or to create an exception boundary.