This change is a bit pedantic, but since these vars aren't accessed
in any hotpath, it's fine to be pedantic. We made these sh_ptrs
atomic so we can use acquire and release side effects when loading
and storing them. This doesn't eliminate the problem of seeing
inconsistent state across microcontrollers, but it helps with simple
accesses like these ones we already do.
We now allocate all the stimFrames for a StimBuffer using a
single StagingBuffer. This gives us all the benefits we're
looking for (pinning, alignment, etc).
hayodea