The SPI sub-system is independent from the uPy state (eg the heap) and so
can safely persist across a soft reset. And this is actually necessary for
drivers that rely on SPI and that also need to persist across soft reset
(eg external SPI flash memory).
The routine waits for the DMA to finish, which is signalled from a DMA IRQ
handler. Using WFI makes the CPU sleep while waiting for the IRQ to arrive
which decreases power consumption. To make it work correctly the check for
the change in state must be atomic and so IRQs must be disabled during the
check. The key feature of the Cortex MCU that makes this possible is that
WFI will exit when an IRQ arrives even if IRQs are disabled.
Header files that are considered internal to the py core and should not
normally be included directly are:
py/nlr.h - internal nlr configuration and declarations
py/bc0.h - contains bytecode macro definitions
py/runtime0.h - contains basic runtime enums
Instead, the top-level header files to include are one of:
py/obj.h - includes runtime0.h and defines everything to use the
mp_obj_t type
py/runtime.h - includes mpstate.h and hence nlr.h, obj.h, runtime0.h,
and defines everything to use the general runtime support functions
Additional, specific headers (eg py/objlist.h) can be included if needed.
This is to keep the top-level directory clean, to make it clear what is
core and what is a port, and to allow the repository to grow with new ports
in a sustainable way.
Damien George
Peter D. Gray