These function attributes are supported by the MSP430 back end:
Critical functions disable interrupts upon entry and restore the
previous interrupt state upon exit. Critical functions cannot also
The MSP430 hardware ensures that interrupts are disabled on entry to
interrupt functions, and restores the previous interrupt state
on exit. The
critical attribute is therefore redundant on
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.
You can provide an argument to the interrupt
attribute which specifies a name or number. If the argument is a
number it indicates the slot in the interrupt vector table (0 - 31) to
which this handler should be assigned. If the argument is a name it
is treated as a symbolic name for the vector slot. These names should
match up with appropriate entries in the linker script. By default
watchdog for vector 26,
nmi for vector 30 and
reset for vector 31 are recognized.
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.
Reentrant functions disable interrupts upon entry and enable them
upon exit. Reentrant functions cannot also have the
critical attributes. They can have the
This attribute only applies to interrupt functions. It is silently ignored if applied to a non-interrupt function. A wakeup interrupt function will rouse the processor from any low-power state that it might be in when the function exits.
On the MSP430 target these attributes can be used to specify whether the function or variable should be placed into low memory, high memory, or the placement should be left to the linker to decide. The attributes are only significant if compiling for the MSP430X architecture.
The attributes work in conjunction with a linker script that has been
augmented to specify where to place sections with a
.upper prefix. So, for example, as well as placing the
.data section, the script also specifies the placement of a
.lower.data and a
.upper.data section. The intention
lower sections are placed into a small but easier to
access memory region and the upper sections are placed into a larger, but
slower to access, region.
either attribute is special. It tells the linker to place
the object into the corresponding
lower section if there is
room for it. If there is insufficient room then the object is placed
into the corresponding
upper section instead. Note that the
placement algorithm is not very sophisticated. It does not attempt to
find an optimal packing of the
lower sections. It just makes
one pass over the objects and does the best that it can. Using the
-ffunction-sections and -fdata-sections command-line
options can help the packing, however, since they produce smaller,
easier to pack regions.