BSP Developer's Guide

VxWorks 5.5
BSP Developer’s Guide
Access Macros
Every access to chip registers should be made through macros that can be
redefined to accommodate different access methods. Usually, just a read and a
write macro should suffice. In some cases, a modify macro to change individual
bits in a register is also needed. For example:
M68681_READ(addr, pData)
M68681_WRITE(addr, data)
M68681_CLR_SET(addr, clear_bits, set_bits)
Accesses to a command block in memory or on a bus must also be through a
redefinable macro to accommodate byte swapping and address manipulation.
Note that read macros are passed the address of where to return the value read.
They do not return a value like a subroutine returns a value. This is deliberate.
Macros written this way can be replaced by a simple statements, subroutine calls,
or by a block statement. Macros written to return a value cannot be replaced by a
C block statement. For example:
xxx = M68681_READ (x); /* Limited */
M68681_READ (x, &xxx); /* Better */
Minimize preprocessor conditional expressions within code blocks. They should
add to the readability of the code, not reduce it. If the conditional only changes the
value of an argument to a routine, it should be done at the beginning of the file
using a #define. Only conditional expressions that actually change the flow of logic
should be within a function.
In this example, the only change is to one argument of a subroutine call. Putting
the conditional statements inside the subroutine only confuses the reader. It does
this because it has absolutely no effect on the flow of execution.
#ifdef INCL_FOO
fooReset (&myFoo,
#else
fooReset (&yourFoo,
#endif
arg2, arg3, arg4);
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