service routine in the case that the requested timer interval is too
small.
Calling the interrupt service routine at this point is likely to
recursively clobber the stack.
Setting a lower bounds on the interrupt delay will limit the upper
speed of pulse generation, but it should not change the relative
pulse rates, and will not recurvisely clobber the stack.
Note that the lower limit of 17 has not been researched, it is
simply the value below which the old code attempted to call
the interrupt service routine directly.
memory barriers since it is only touched inside a single interrupt
handler or while interrupts are disabled in setTimer().
This saves about 90 bytes since it no longer needs to be reloaded multiple
times.
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
Doing so adds most of the interrupt execution time to the
step time, see line 126 of the same file:
if (next_step_time == 0) {
// new move, take current time as start value
step_start = TCNT1;
}
The old implementation with an overflow interrupt for the clock and a comparator interrupt for stepping, had an unsolvable bug: If the comparator interrupt should happen very shortly after the overflow interrupt the comparator interrupt would miss. And with 2 comparators the implementation is more straightforward.
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.
Jim McGee
Michael Moon
Markus Hitter
Markus Amsler