Function:

FSAVE saves the FPU internal registers (including ST-registers) and the
environment to the memory operand. See <FPU State image layout>.

The FPU does not execute this instruction until all pending FPU
operations have completed (decoded instructions have been processed).
After completion, FSAVE initializes the FPU as if it had executed FINIT.

Apparently on all FPUs, the contents of the data pointer field is
undefined if the last FPU arithmetic instruction did not use a memory
operand.

On some 386s operating in Real or V86 mode, the opcode saved is incorrect.
The linear address saved for the opcode's address however is correct and
can be used to retrieve the opcode. No opcode is saved in Protected mode.

If either of the two last bytes of the image being saved by FSAVE cannot
be accessed for whatever reason, the instruction cannot be restarted on
some 387s.

A workaround is to attempt to write to those bytes before the FSAVE is
executed or to align the image on a 128 byte boundary so it is
unlikely to fall outside a segment or page boundary.
Should that be the case, the integer unit can cause an exception or
make sure the page (in case of a swapped page) is read into memory
before FSAVE starts.




FSETPM  Make FPU use Protected Mode format in FSAVE and FSTENV
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