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Using conditionals within shared (C & ASM) header file

Steve Mutschler

Last June, someone asked about how command line symbols defined for both the assembler and the C compiler could be referenced within a conditional (if) statement within a universal shared header file. A company rep said they'd forward this to the tech team for advice. Whatever happened?

The issue is this: Symbols of identical name specified on the command line for the assembler and the C compiler end up being unique symbols. Those specified for the assembler are defined as per a "$set" directive and are visible only to the assembler. Those specified for the C compiler are defined as per a "#define" directive and are only visible when running the compiler.

In other words, there is no way to define a symbol on the A51 assembler command line that will be visible to the C preprocessor within the assembler. Symbols defined this way are only visible to "$if" statements.

PROBLEM: A universal header file containing an "#ifdef SYMBOL" conditional branch will work within C modules, but will not work within assembler modules because the assembler's C preprocessor WILL NOT recognize the referenced symbol and will thus test false.

Example:

#ifdef SYMBOL
  #include <me.h>
#endif
will test as false within the assembler C macro preprocessor if SYMBOL is only defined on the command line. Of course, an explicit
#define SYMBOL
appearing before the conditional will force the condition to be TRUE, but that is not what we are trying to do here. We want the command line argument to trigger different code versions, for example, to target different hardware configurations.

So it's 2005. Any solutions to this dilemma yet?

Parents
  • 0 in reply to erik malund

    Often I have to make several to separate out what the assembler can not handle.

    Hmm... what's wrong with just putting a big 

    #ifdef __C51__
/* ... */
#endif
    around those parts A51 can't understand? If you don't like the dependency on the vendor-specific macro __C51__, just use __STDC__ or any other macro name you like (and set up in the makefile or project C options, accordingly)

Reply
  • 0 in reply to erik malund

    Often I have to make several to separate out what the assembler can not handle.

    Hmm... what's wrong with just putting a big 

    #ifdef __C51__
/* ... */
#endif
    around those parts A51 can't understand? If you don't like the dependency on the vendor-specific macro __C51__, just use __STDC__ or any other macro name you like (and set up in the makefile or project C options, accordingly)

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