BSP Developer's Guide

8
Writing Portable C Code
attribute declaration. It is placed after the closing curly brace, but before any
instance declarations or initializers. By including the vxWorks.h header file in your
compilation, a toolchain specific header file is included to define this macro
appropriately for the compiler tool being used.
For example:
struct aPackedStruct {
UINT32 int1;
INT16 aShort;
INT8 aByte;
} _WRS_PACK_ALIGN(1);
struct aPackedStruct {
UINT32 int1;
INT16 aShort;
INT8 aByte;
} _WRS_PACK_ALIGN(1) anInstance = {0x1, 2,3};
8
typedef struct {
UINT8 aByte;
UINT16 aShort;
UINT32 aLong;
} _WRS_PACK_ALIGN(1) myPackedStruct;
Specify Field Widths
Always use specific field widths within a packed structure declaration. The basic
data type int does not have a specific size and should be avoided. The same rule
applies for long, unsigned, and char. The vxWorks.h header file defines basic data
types with explicit sizes. Use these data types in any packed structure (INT8,
INT16, INT32, UINT8, and so on). In general, think ahead to architectures with
more than a 32-bit native integer.
Avoid Bit Fields
Do not include bit field definitions within a packed structure. Compilers are
permitted to start labeling bits with either the least significant bit or the most
significant bit. This issue can be dealt with easily by using macro constants to
define the specific bit pattern within the data field.
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