See https://github.com/micropython/micropython/issues/1736 for the
list of complications. This workaround instead of duplicating REPL
to another stream, switches to it, because read(STDIN) we use otherwise
is blocking call, so it and custom REPL stream can't be used together.
POSIX doesn't guarantee something like that to work, but it works on any
system with careful signal implementation. Roughly, the requirement is
that signal handler is executed in the context of the process, its main
thread, etc. This is true for Linux. Also tested to work without issues
on MacOSX.
This solves long-standing non-deterministic bug, which manifested itself
on x86 32-bit (at least of reported cases) - segfault on Ctrl+C (i.e.
SIGINT).
py/mphal.h contains declarations for generic mp_hal_XXX functions, such
as stdio and delay/ticks, which ports should provide definitions for. A
port will also provide mphalport.h with further HAL declarations.
These MPHAL functions are intended to replace previously used HAL_Delay(),
HAL_GetTick() to provide better naming and MPHAL separation (they are
fully equivalent otherwise).
Also, refactor extmod/modlwip to use them.
This gets uPy readline working with unix port, with tab completion and
history. GNU readline is still supported, configure using
MICROPY_USE_READLINE variable.
