BSP Developer's Guide

8
Writing Portable C Code
Always specify fields with explicit widths, such as UINT8, UINT16, INT32, and so
on. Do not use bitfields in a packed structure.
_WRS_ASM(“X”)
This macro is used to insert assembly code within a C function declaration. The
inserted code must not interact with C variables or try to alter the return value of
the function. The code uses the MIT assembly-language mnemonics and syntax.
It is assumed that the compiler does not optimize or reorder any specified in-line
assembly code. The insertion of a null in-line assembly statement can be used to
prevent the compiler from reordering C code before the statement with C code that
follows the statement.
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_WRS_DATA_ALIGN_BYTES(n)
This macro is used in prefix notation to declare an initialized C data element with
a special alignment. The argument n is the alignment in byte units (1, 2, 4, 8, 16, and
so on). This is normally used only with initialized global data elements. Use this
macro with caution: overuse of this macro can result in poor memory utilization.
If large numbers of variables require special alignment, it may be best to declare
them in separate sections directly in assembler. The linker loader could then fit
them together in an optimal fashion.
_WRS_GNU_VAR_MACROS
The GNU compiler system created a means to pass a variable number of
arguments to pre-processor macro functions, and there are a few special instances
in the VxWorks code base that use the GNU-defined syntax. Since then, the ANSI
standards committee has defined an ANSI standard that is different from this
practice. Currently, the GNU compiler 2.96 does not yet support the ANSI
standard, and the Diab compiler supports only the ANSI standard.
Code that does use variadic macros should define them both for GNU and for the
ANSI standard (Diab). Rather than select upon the toolchain or compiler name, a
new macro feature name, _WRS_GNU_VAR_MACROS, has been created. The GNU
toolchain defines this macro; the Diab toolchain does not.
If you want to port your code to another toolchain, you must choose between
supporting the GNU-style syntax or the ANSI standard syntax. For example, the
following code fragment demonstrates the use of an #ifdef statement to make this
choice between GNU and ANSI:
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