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error C258:mspace illegal in struct/union

naresh rana

Hi all
i want to read RTC time parameters.
RTC is treated as one of memory location,it gets enabled when parameters are refered.
following where the codes:

struct tm{
unsigned char xdata second  _at_(0xe000);
unsigned char xdata minute  _at_(0xe002);
unsigned char xdata hour    _at_(0xe004);
};

void main()
{
 struct tm time;
 printf("seconds %x",time.second)
 ...
}
On compiling above code compiler gives following error:
error C258:mspace has illegal in struct/union.

but if code in struct are modified as follows:
struct tm{
unsigned char second _at_(0xe000);
}
Code compiles without any error but RTC was not getting enabled by
addr-decod logic even on disabling internal xram from AUXR.

but if my codes are as follows than things work perfect:

xdata unsigned char second  _at_(0xe000);
xdata unsigned char minute  _at_(0xe002);
xdata unsigned char hour    _at_(0xe004);

void main()
{
  printf("\nseconds %x",second);
  printf("\nminutes %x",minutes);
  printf("\nhours   %x",hour);
}

1)what is wrong with the defn in struct ?
2)i cannot just define struct as xdata because
addr-decoding logic should enable RTC when required,
so how can i declare struct variable so that no error is generated and RTC is enabled ?
3)what if i try to define more than one struct var for above case ?
eg
 struct tm{
 unsigned char xdata second  _at_(0xe000);
 unsigned char xdata minute  _at_(0xe002);
 unsigned char xdata hour    _at_(0xe004);
 };

 void main()
 {
  struct tm time1,time2;
  ......

will var in time1 and time2 be placed in same location ?

Regards
Naresh

Parents
  • 0 in reply to Bernhard Felkel

    Thanks for reply.
    with following code:

    struct tm
{
	unsigned char second;
	unsigned char res1;
	unsigned char minute;
	unsigned char res2;
	unsigned char hour;
};
struct tm xdata time _at_ 0xe000; 	// time starts at 0xe000 !!

void main()
{
}

    will compiler assign following addrress for struct elements ?

    second --> 0xe000
    res1 --> 0xe0001
    minute --> 0xe002
    res2 --> 0xe0003
    hour --> 0xe004


    what if i define: 
    struct tm xdata time1 _at_ 0xe000;
struct tm xdata time2 _at_ 0xe000;
    will the elements of both struct time1 and time2 refer same location ?
    changes made in elements of time1,will disturb elements of time2 ?

    Regards
    Naresh

Reply
  • 0 in reply to Bernhard Felkel

    Thanks for reply.
    with following code:

    struct tm
{
	unsigned char second;
	unsigned char res1;
	unsigned char minute;
	unsigned char res2;
	unsigned char hour;
};
struct tm xdata time _at_ 0xe000; 	// time starts at 0xe000 !!

void main()
{
}

    will compiler assign following addrress for struct elements ?

    second --> 0xe000
    res1 --> 0xe0001
    minute --> 0xe002
    res2 --> 0xe0003
    hour --> 0xe004


    what if i define: 
    struct tm xdata time1 _at_ 0xe000;
struct tm xdata time2 _at_ 0xe000;
    will the elements of both struct time1 and time2 refer same location ?
    changes made in elements of time1,will disturb elements of time2 ?

    Regards
    Naresh

Children
  • 0 in reply to naresh rana

    "will compiler assign following addrress for struct elements?"

    I think you need to go back to your 'C' textbook and read-up on the way structures work.

    what if i define:

    struct tm xdata time1 _at_ 0xe000;
struct tm xdata time2 _at_ 0xe000;

    You have declared two different variables at the same memory address - this will probably give you a Linker error!

    Why would you want to do this?