These function attributes are supported by the AVR back end:
On the AVR, the hardware globally disables interrupts when an
interrupt is executed. The first instruction of an interrupt handler
declared with this attribute is a
SEI instruction to
re-enable interrupts. See also the
signal function attribute
that does not insert a
SEI instruction. If both
interrupt are specified for the same function,
is silently ignored.
asmstatements can safely be included in naked functions (see Basic Asm). While using extended
asmor a mixture of basic
asmand C code may appear to work, they cannot be depended upon to work reliably and are not supported.
OS_taskattribute do not save/restore any call-saved register in their prologue/epilogue.
OS_main attribute can be used when there is
guarantee that interrupts are disabled at the time when the function
is entered. This saves resources when the stack pointer has to be
changed to set up a frame for local variables.
OS_task attribute can be used when there is no
guarantee that interrupts are disabled at that time when the function
is entered like for, e.g. task functions in a multi-threading operating
system. In that case, changing the stack pointer register is
guarded by save/clear/restore of the global interrupt enable flag.
The differences to the
naked function attribute are:
nakedfunctions do not have a return instruction whereas
OS_taskfunctions have a
nakedfunctions do not set up a frame for local variables or a frame pointer whereas
OS_taskdo this as needed.
See also the
interrupt function attribute.
The AVR hardware globally disables interrupts when an interrupt is executed.
Interrupt handler functions defined with the
do not re-enable interrupts. It is save to enable interrupts in a
signal handler. This “save” only applies to the code
generated by the compiler and not to the IRQ layout of the
application which is responsibility of the application.
interrupt are specified for the same
signal is silently ignored.