data type bug or not....

I've noticed that the following definitions generate different data
results. Perhaps, I'm overlooking something.

#define TEMP (*(unsigned char xdata *) 0x10F0))

unsigned char xdata sutton2, *sutton;
unsigned char xdata * xdata sutton3;

sutton = &TEMP;
sutton3 = &TEMP;
sutton2 = TEMP;

If XDATA location 0x10F0 has 0x35, then the following compilation
occurs:

'sutton' has the value X:10F0, which is correct.
'sutton2' has the value 0x35, which is correct.
'sutton3' has the value D:10F0, which is not correct.

To complicate things, if I swap the 'sutton2' and 'sutton' declarations to:

unsigned char xdata *sutton, sutton2;

then 'sutton' has the value D:10F0, which is not correct.

There is no DATA location 10F0, therefore garbage is the result.

The source code generated for *sutton being first in the declaration
list is a 2 byte XDATA pointer, which points to the DATA area.

If *sutton is not the first declaration in the list, it is a 3 byte pointer
(which works correctly) that points to XDATA.

Anyone know what the problem is and why the sutton3 declaration
listed above does not force the compiler to generate a pointer that
points to XDATA?

Thanks

Sutton Mehaffey
Lookout Portable Security
sutton@lookoutportablesecurity.com


Parents
  • I tried the following:

    unsigned char xdata TEMP _at_ 0x10f0;
    
    unsigned char xdata sutton2, *sutton;
    unsigned char xdata * xdata sutton3;
    
    
    void main (void)
    {
    	sutton = &TEMP;
    	sutton3 = &TEMP;
    	sutton2 = TEMP;
    
    }
    

    looked at the generated code, and at the simulator. Both worked fine. I used the _at_ language extension as a test, but the original code using the #define also worked correctly.

Reply
  • I tried the following:

    unsigned char xdata TEMP _at_ 0x10f0;
    
    unsigned char xdata sutton2, *sutton;
    unsigned char xdata * xdata sutton3;
    
    
    void main (void)
    {
    	sutton = &TEMP;
    	sutton3 = &TEMP;
    	sutton2 = TEMP;
    
    }
    

    looked at the generated code, and at the simulator. Both worked fine. I used the _at_ language extension as a test, but the original code using the #define also worked correctly.

Children
No data
More questions in this forum