CodeWarrior for MCUのトピックRe: type casting in CW12 V3.1

type casting in CW12 V3.1

markiscarabas — Sat, 13 May 2006 03:10:29 GMT

Hi,

I have the question on typecasting mechanism :

The simple code is below (small memory model):

typedef struct

{

char low;

char high;

}SPLIT_T;

const unsigned char test_ch = (unsigned char )&handler; // Does not work ...storage dest is too small. I understand and would expect that test_ch would contain either msb or lsb of the handler's address!?

const SPLIT_T test_split = (SPLIT_T )&handler; // Compiler complaines - illegal typecast ????

void handler(void);

void main(void)

{

...

}

void handler(void)

{

...

}

Any ideas...

Regards, Mark

Re: type casting in CW12 V3.1

marc_paquette — Mon, 15 May 2006 21:17:44 GMT

Pointer types may only be converted to other pointer types (and to the integer type). In your case, try this:

htype* handler;

typedef struct

{

char low;

char high;

} SPLIT_T;

const SPLIT_T* test_ptr = (SPLIT_T*)&handler;

// test_ptr->low points to lower handler's address and test_ptr->high points to higher part of address, assuming processor is running in low-endian mode.

Marc.

Re: type casting in CW12 V3.1

Lundin — Thu, 18 May 2006 20:16:14 GMT

The name "handler" is to be regarded as a function pointer. So there is no need to take the address of it. This should work:

typedef struct
{
char low;
char high;
}SPLIT_T;

void handler (void);

const SPLIT_T test_split = *(SPLIT_T*)handler;

And as mentioned, which part of the address that ends up where depends on little/big endian.

Since you seem to be using HC12 with big endian, you should swap the order of low/high.

On HC12, you also need to be careful with where you place "handler" in the memory. If you place it in banked flash, it would suddenly become a 3-byte "far" pointer where the ms byte is the flash page.