After chatting with the MAC team, the TSF writes (at least on the 11n
MACs, I don't know about pre-11n MACs) are done as 64 bit writes that
can take some time. So, doing a 32 bit TSF write is definitely not
supported. Leave a comment here which explains that.
Whilst here, add a comment which outlines that after a reset or TSF
write, the TSF write may take a while (up to 50uS) to update.
A write or reset shouldn't be done whilst the previous one is in
flight. Also (and this isn't currently done) a read shouldn't
occur until the SLEEP32_TSF_WRITE_STAT is clear. Right now we're
not doing that, mostly because we haven't been doing lots of TSF
resets/writes until recently.