Accessing bit fields using a union problem.

[samdomville]

Hello - I changed my code from my last post:
http://cboard.cprogramming.com/showthread.php?t=109945
so that the struct of bit fields is unionized with a UINT32 word:

#include <stdio.h>


typedef union 
{
    struct {

    /// Reserved - read as 0
    unsigned reserved : 30;

    /** This bit contains the interrupt status. Reading this register
     * clears this bit.
     */
    unsigned stats : 1;

    /** This field masks the interrupt.
     *	0 - Masked
     *	1 - Enabled
     */
    unsigned maskn : 1;

    } bits;

    unsigned long word;

} volatile RegStruct;

RegStruct *hwReg

When I print out hwReg.word I get the entire correct 32 bits - BUT when I print out one of the bits hwReg.bits.maskn, I get 0x00000000 - I think it still may be accessing the bits as bytes even though the struct is unionized with UINT32. what is going on?

[tabstop]

I assume you're printing with %x? %x says "the thing I am handing you is an unsigned int". If the thing you are printing is not an unsigned int, well, then, that's too bad -- it's going to be printed as an unsigned int.

[samdomville]

Why yes we are printing with a %x and all the bytes that are displayed are positive status bits, so they are unsigned. Can you please help still?

[matsp]

Show us the code that does the printing.

--
Mats

[samdomville]

void putHex(UINT32 x)
{
    printf("0x%x ", x);
}

but could it have to do with something about union and struct in my code instead?

[slingerland3g]

Have you by any chance intialized RegStruct.word as well as RegStruct.bits.maskn or any other bit variable? That is not advisable when using a union as they share the same memory of the larger of the two defined variables.

[matsp]

Right, can you please post all (or at least a decent part) of the code, as we need some context to answer this question, I think.

--
Mats