These function attributes are supported by the AVR back end:
Use this attribute to indicate that the specified function is an interrupt handler. The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.
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.
This attribute allows the compiler to construct the
requisite function declaration, while allowing the body of the
function to be assembly code. The specified function will not have
prologue/epilogue sequences generated by the compiler. Only basic
asm statements can safely be included in naked functions
(see Basic Asm). While using extended
asm or a mixture of
asm and C code may appear to work, they cannot be
depended upon to work reliably and are not supported.
Do not use
__gcc_isr pseudo instructions in a function with
signal attribute aka. interrupt
service routine (ISR).
Use this attribute if the preamble of the ISR prologue should always read
push __zero_reg__ push __tmp_reg__ in __tmp_reg__, __SREG__ push __tmp_reg__ clr __zero_reg__
and accordingly for the postamble of the epilogue — no matter whether the mentioned registers are actually used in the ISR or not. Situations where you might want to use this attribute include:
SREGother than the
I-flag by writing to the memory location of
__gcc_isr generation for the whole compilation unit,
there is option -mno-gas-isr-prologues, see AVR Options.
On AVR, functions with the
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.
Use this attribute on the AVR to indicate that the specified function is an interrupt handler. The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.
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.