Re: [avr-gcc-list] Pointer to a function in a structure in flash?

[E . Weddington]

> 
> I'm having more problems converting code from IAR to GCC, 
in getting
info>  
> from
> flash:
> 
> I have this structure:
> 
> typedef struct /* define the struct 'cmd_entry' */
> {
>      /* Pointer to string in flash: */
>      PGM_P command;
> 
>      /* Pointer to function in flash returning an int, 
passed a char 
> pointer: */
>      uint16_t  (*function)(CONST char * tok_buf, CONST 
char * tok_ptr);
> }str_func_entry;
> 
> This IAR code does what I want:
>      flash_str_out( cmd_func_table[i].command );
> 
> which to get to work in GCC I had to change to this:
> 
>      flash_str_out( (PGM_P) pgm_read_word( &cmd_func_table
[i].command )
)> ;
> 
> However I can not figure out the right magic words to 
convert this 
> section, that has a
> pointer to a function in a structure in flash:
> 
> Working IAR code snippet (STRCMP = strcmp_P):
>   /* If find a table match then call that function: */
>   if( !STRCMP( (const char *) token , cmd_func_table
[i].command ) )
>   {
>    /* Call the function from the function table: */
>    retval = ( *(cmd_func_table[i].function) )( (char 
const *) token,
(c> har 
> const *) tokptr );
>   }
> 
> I tried this, and other variations, with various casts:
>    retval = ( *(pgm_read_word( &cmd_func_table
[i].function )) )( (char 
> const *) token, (char const *) tokptr );
> 
> but then I get errors like "object is not function" or
>   "invalid type argument of 'unary *'".
> 
> Suggestions?
> 

You're close. What you need to do is to typecast the 
pointer that is returned from pgm_read_word() to the type 
that it is pointing to (the particular function) before 
dereferencing the pointer and calling the function.

Unfortunately this could look a bit messy without doing 
some additional typedefs beforehand. I would suggest this 
(sorry for the gratuitous wrapping):

typedef uint16_t (*functype_t)(CONST char * tok_buf, CONST 
char * tok_ptr);

typedef struct
{
     PGM_P command;
     functype_t function;
}str_func_entry;


retval = (*((functype_t)(pgm_read_word(&cmd_func_table
[i].function))))((char const *)token, (char const *)tokptr);

this is untested of course.

HTH
Eric