Accessing single bits

[drumfirex]

Posted on July 01, 2003 at 07:03

Accessing single bits

[drumfirex]

Posted on June 30, 2003 at 07:19

I use Codewarrior compiler and I want to access bits in this way:

typedef struct Type_AnIn {

signed short Value;

unsigned char Ampli :4;

unsigned char Status :4;

};

struct Type_AnIn AnIn; /* size: 3 bytes */

void Test(void)

{

unsigned char Aux;

/* Example */

AnIn.Ampli = 3; /* write access --> warning */

AnIn.Status = 0; /* write access --> warning */

AnIn.Value = -20; /* no warning */

AnIn.Status = 0; /* write access --> warning */

Aux = AnIn.Ampli; /* read access --> no warning */

}

The compiler generate the following message only when I tried to write bit access structure fields:

C3604 Static '_xxPSID1' was not referenced.

I think.......there is something wrong

Thanks, Patrik

[parveen]

Posted on July 01, 2003 at 02:24

I tried to run similar code on Hiware Compiler and there is no problem with bitfield operation.

There may be some other problems in the code

Regards,

PraveenG

[drumfirex]

Posted on July 01, 2003 at 07:03

You are correct, I omit some informations because I thought the ''error'' happened anyway....sorry.

The code is like this:

struct Type_AnIn AnIn[3];

void Test(void)

{

unsigned char Ix;

for (Ix = 0; Ix < 3; Ix++)

AnIn[Ix].Ampli = AMP_NTC;

}

When I select the ''error'' to point the code that generates it, the Codewarrior highlight the line above header of the next function....

The ''problem'' doesn't occur if I use:

AnIn->Ampli = AMP_NTC;

The ''problem'' doesn't occur if I use:

typedef struct Type_AnIn {

signed short Value;

unsigned char Ampli;

unsigned char Status:4;

};

If I open the map file, I see that when I access a bit mapped field the compiler generates a variable (_xxPSID1) in the overlap segment.

C3604 is not an error nor a warning, it's only an ''information'' message...but I want to know why...

Thanks for your help,

Patrik