This prevents nasty surprises because this restriction is not mentioned in the configuration files. It also allows better tuning of performance against memory usage.
Traumflug: costs 18 bytes flash, so it's bearable.
Specifically, disable interrupts just before returning and then enable
the timer interrupt if appropriate. This means that the timer interrupt
cannot actually fire until after the RETI, so the function cannot be
entered recursively.
manage the movebuffer (mb_head, mb_tail, movebuffer).
The approach taken is to leave all of the variables non-volatile
and use memory barriers to control reads/writes. read/modify/write
operations that can be done outside of the interrupt context are
protected by disabling interrupts.
Also, manually cache the pointer to the movebuffer of interest
as the compiler does a poor job of reusing the pointer even in
places that it could.
There are still some groups of accesses to the movebuffer data that need
to be protected by disabling interrupts, but these are all related
to sending back debug data. The error will cause occassional mismatched
values to be sent back via the serial connection, but they do not
affect the actual operation of the code, so they will be addressed
in a separate checkin.
Conflicts:
dda_queue.c
This costs 2 bytes of ram, but saves 60 bytes of flash. Doing so
also eliminates the need to disable interrupts while clearing flags
in the ifclock macro.
Conflicts:
clock.c
timer.c
timer.h
After lots of try and error the conclusion was, disabling this
interrupt makes the timer vulnerable to be messed up by
characters incoming over the serial line. So, now the
interrupt is enabled as a move starts and not disabled before
the move, and all subsequent moves are done.
Markus Hitter
Ben Gamari
Bas Laarhoven
Jim McGee
Michael Moon
Stephan Walter