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Problem writing DWORD xdata

Jonathan Kaufmann

I just noticed this recently... whenever I have a xdata DWORD - 32 bits - and I try to set it to a constant value (or any value I think), the assembly that gets generated seems all messed up for such a simple routine. See below. Writing a WORD (TotalSleepTime.m16.ab) works fine, but writing a DWORD (NextSleepTime), makes a call to some external routine which is excessively long and then has a series of NOPs.

    77:         TotalSleepTime.m16.ab = 0;
C:0x3347    900181   MOV      DPTR,#TotalSleepTime(0x0181)
C:0x334A    F0       MOVX     @DPTR,A
C:0x334B    A3       INC      DPTR
C:0x334C    F0       MOVX     @DPTR,A
    78:         TotalSleepTime.m16.cd = 0;
    79:
C:0x334D    900183   MOV      DPTR,#0x0183
C:0x3350    F0       MOVX     @DPTR,A
C:0x3351    A3       INC      DPTR
C:0x3352    F0       MOVX     @DPTR,A
    80:         NextSleepTime = 1;
C:0x3353    900185   MOV      DPTR,#NextSleepTime(0x0185)
C:0x3356    120FB2   LCALL    C?LSTKXDATA(C:0FB2)
C:0x3359    00       NOP
C:0x335A    00       NOP
C:0x335B    00       NOP
C:0x335C    0122     AJMP     C:3022

I noticed that something like

variable.m32.abcd = 0

would generate screwed up code like this, so I though it may have to do with the union not being accessed correctly, so I tried changing a variable just to a straight up DWORD (NextSleepTime as seen above), but the same thing happens.

Is this behavior normal? I can't follow the undocumented assembly that is called very well, but it definitely seems excessively complicated for a simple command. I just checked on a blank project with

void main(void)
{
   unsigned long xdata test;
   test = 0;
}

Same thing.

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