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4. Customising ccg's behaviour

Several aspects of the runtime assembler and preprocessor can be customised for a particular client program. This is occasionally useful and not difficult for assembler ``wizards'' to do, but it does require a certain familiarity with the preprocessor and runtime assemblers. If in doubt, seek professional help.

4.1 Customising the runtime assembler

The runtime assemblers share a common framework in which several actions can be changed from their defaults by the client program. The customisable operations are:

• the actions associated with the start and end of dynamic code sections, corresponding to the directives ``#['', ``#{'', ``]#'' and ``}#''.
• the action associated with the ``.org'' pseudo-op.
• the action associated with the definition of a program label, corresponding to ``name:''.

Customisation is achieved by defining one or more macros before using the #cpu directive. The macros concerned, and their default definitions, are as follows:

• the action associated with ``#[''

     #define _ASM_APP_1      { asm_pass= 0; {

• the action associated with ``]#''

     #define _ASM_NOAPP_1    } asm_hwm= asm_pc; }

• the action associated with ``#{''

     #define _ASM_APP_2      { for (asm_pass= 1; asm_pass < 3; ++asm_pass) {

• the action associated with ``}#''

     #define _ASM_NOAPP_2    if (asm_pass==1) asm_hwm= asm_pc; \
                             else if (asm_hwm!=asm_pc) ASMFAIL("phase error"); } }

• the action associated with the pseudo-op ``.org O''

     #define _ASM_ORG(O)     (asm_pc= (O))

• the action associated with label declaration ``.label N''

     #define _ASM_LBL(N)     static insn *N= 0

• the action associated with label definition ``N:''

     #define _ASM_DEF(N)     (N= (((asm_pass==2)&&(asm_pc!=(N))) \
                                  ? (insn *)ASMFAIL("phase error") : asm_pc))

4.2 Customising the preprocessor

Several preprocessor characteristics can be altered by changing definitions near the beginning of the source file ccg.c and then recompiling. The customisable definitions and their default values are as follows:

• the prefix added to the canonical target name in the #include directive corresponding to the #cpu declaration

     #define HEADER_PREFIX   "ccg/asm-"

• the set of characters that can appear in labels (some clients may want to add the dollar sign (`$') to this list)

     #define LABEL_CHARS     "_A-Za-z0-9"

• the ``tokens'' recognised as the start and end delimiters of one- and two-pass dynamic code sections

     #define ASM_1_OPEN      "#["
     #define ASM_1_CLOSE     "]#"
     #define ASM_2_OPEN      "#{"
     #define ASM_2_CLOSE     "}#"

4.3 Customisation example

One simple but useful customisation is to implement automatic synchronisation of the instruction and data caches at the end of each dynamic assembler section. One way to achieve this is as follows:

... header files or other preambulae ...

/*** customised runtime assembler actions: add automatic iflush(lwm,pc) ***/

#define _ASM_NOAPP_1    } iflush(asm_lwm, asm_pc); asm_lwm= asm_pc; }

#define _ASM_NOAPP_2    if (asm_pass==1) asm_hwm= asm_pc; \
                        else if (asm_hwm!=asm_pc) ASMFAIL("phase error"); \
                        else { iflush(asm_lwm, asm_pc); asm_lwm= asm_pc; } } }

#define _ASM_ORG(ADDR)  if (asm_lwm != 0) iflush(asm_lwm, asm_pc); \
                        (asm_lwm= asm_pc= (ADDR))

#cpu nameOfTargetCPU

/* the following variable must be _defined_ in only ONE program file */

extern insn *asm_lwm;   /* "low water mark" for cache flush */

/*** end of customised runtime assembler actions ***/

... program ...