MSP430 Function Attributes#
These function attributes are supported by the MSP430 back end:
- critical#
Critical functions disable interrupts upon entry and restore the previous interrupt state upon exit. Critical functions cannot also have the
naked
,reentrant
orinterrupt
attributes.The MSP430 hardware ensures that interrupts are disabled on entry to
interrupt
functions, and restores the previous interrupt state on exit. Thecritical
attribute is therefore redundant oninterrupt
functions.
- interrupt#
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 the names
watchdog
for vector 26,nmi
for vector 30 andreset
for vector 31 are recognized.
- naked#
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 — Assembler Instructions Without Operands). While using extendedasm
or a mixture of basicasm
and C code may appear to work, they cannot be depended upon to work reliably and are not supported.
- reentrant#
Reentrant functions disable interrupts upon entry and enable them upon exit. Reentrant functions cannot also have the
naked
orcritical
attributes. They can have theinterrupt
attribute.
- wakeup#
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.
- lower, upper, either#
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 in the large memory model.
The attributes work in conjunction with a linker script that has been augmented to specify where to place sections with a
.lower
and 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 is thatlower
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.The
either
attribute is special. It tells the linker to place the object into the correspondinglower
section if there is room for it. If there is insufficient room then the object is placed into the correspondingupper
section instead. Note that the placement algorithm is not very sophisticated. It does not attempt to find an optimal packing of thelower
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.