wbflush − wait until all R2000 memory writes have completed

wbflush()

busy waits until the R2020 write buffers indicate that all R2000 memory
writes have be completed.  Wbflush is necessary in two situations:
1
Where writing to one memory location may affect the contents read from
another location.  An example of this is writing to device controllers
where a command may be written into one device register and status
read from another.
2
Where writes to contiguous byte or halfword locations must be gathered
in to larger units by the "byte gathering" mechanism of the write
buffers.
Wbflush is implemented by spinning on the coprocessor 0 condition
code, this is a function of the R2300 cpu board and may not be
implemented on boards other than the R2300.