in the Xous context, because the IRQ banks are owned by a global
object, not every server can simply refer to the IRQ bits by just
dereferencing a pointer. Instead, it needs to send a message to
the cram_hal_service with an API number which then catches this
and does the dereference on behalf of the caller.
multiple IRQs related to the UDMA will eventually get mapped into
the global IRQ handler for UDMA. Create an enum type that will
help us differentiate this and add a trait that returns the raw bits
for a given IRQ type.
Probably a fancier wrapper should be made to interptet the IRQ
bits but unfortunately there isn't a uniform pattern to the IRQ
mappings, it's pretty much whatever fit into the IRQ space based
on the underlying function. At the moment not even sure if this
is the right register to be chasing, so we'll use this for probing
that aspect and then get fancy later, maybe.
This is a distillation of cramium-hal items into "pure API"
items so that we can have a parallel cramium-emu crate.
The idea is that the API crate sits on top of both implementations;
the HAL goes to hardware, and EMU goes to hosted mode emulations.
