Fixes#5745
For AVR based boards, three defines must be defined AVR_CONTEXT_SWAP_INIT,
AVR_CONTEXT_SWAP_INTERRUPT_VECT, and AVR_CONTEXT_SWAP_TRIGGER.
These defines are used to trigger a software interrupt used for context
switching.
When AVR_CONTEXT_SWAP_INTERRUPT_VECT is handled, the scheduler is run
and a context swap will happen if necessary, with the resulting thread
starting following the reti instruction. This results in threads running
at normal priority instead of at interrupt priority.
Atmega devices do provide a pure software interrupt. The method used
here for waspmote-pro and arduino-mega2560 is to use pin change
interrupts, set the pin to act as an output, and toggle the value to
simulate a software interrupt. The main limitation here is that a
physical pin is now occupied and must be defined for each board
supported by RIOT. On the plus side, it provides an easy method for
detecting context swaps with an oscilloscope.
* also added a trailing underscore to header guards for consistency
Commit for PR 2623, repairing header file include guards.
This PR is intended to fix the include guards in files under RIOT/boards
SQUASH ME: fix underscore removal overdos
SQUASH ME: consistent macro naming
SQUASH ME: missed that one
SQUASH ME: fixed overdo
SQUASH ME: consistency
