This was originally used for non-event based REPL processing. Then it
was unused when event-based processing was activated. But now that event
based is disabled, and non-event based is back, there has been new ring
buffer code to process the chars.
Event-driven loop (push-style) is still supported and default (controlled
by MICROPY_REPL_EVENT_DRIVEN setting, as expected).
Dedicated loop worked even without adding ets_loop_iter(), though that
needs to be revisited later.
Before this change, if REPL blocked executing some code, it was possible
to still input new statememts and excuting them, all leading to weird,
and portentially dangerous interaction.
TODO: Current implementation may have issues processing input accumulated
while REPL was blocked.
The idea is following: underlying interrupt-driven or push-style data source
signals that more data is available for dupterm processing via call to
mp_hal_signal_dupterm_input(). This triggers a task which pumps data between
actual dupterm object (which may perform additional processing on data from
low-level data source) and input ring buffer.
But now it's generic ring buffer implemented via ringbuf.h, and is intended
for any type of input, including dupterm's, not just UART. The general
process work like this: an interrupt-driven input source puts data into
input_buf, and then signals new data available via call to
mp_hal_signal_input().
Features inline get/put operations for the highest performance. Locking
is not part of implementation, operation should be wrapped with locking
externally as needed.
Paul Sokolovsky
Damien George
Stephen Kyle
Pavol Rusnak