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Hi everybody,
I would like to access a variable in XDATA from different .c source files.
Obviously, that doesn't work the way i'm doing it, but what am I doing wrong?
Here is a tiny code example that shows the problem:
8<----------------------------------------- (main.c) unsigned char xdata receivedstring[1] _at_ 0x124; unsigned char a; void testfunction(void);
void main(void) { receivedstring[0]='q'; a=receivedstring[0]; testfunction(); while(1); }
8<----------------------------------------- (test.c) extern unsigned char xdata receivedstring[1] _at_ 0x124; unsigned char b; void testfunction(void);
void testfunction(void){ b = receivedstring[0]; //doesn't work }
8<-----------------------------------------
I would expect the variable 'b' to be set to 'q' at the end of the program. Watching at receivedstring[0] in the testfunction shows that its content is 'q' at address 0x0124, but the assembly shows that the content of 0x0000 instead of 0x0124 is assigned to the variable 'b':
8<----------------------------------------- //assembly translation:
7: void testfunction(void){
8: b = receivedstring[0]; C:0x001A 900000 MOV DPTR,#0x0000 //why not "DPTR,#0x0124" ? C:0x001D E0 MOVX A,@DPTR C:0x001E F509 MOV b(0x09),A
9: } C:0x0020 22 RET
Thanks for any help!
Tobias
Thanks for your answer. Yes, my device has internal XRAM. After Please read the manual-ming for a while, I'm pretty sure, that i enable it in the startup file the right way:
8<----------------------------------------
XDATASTART EQU 0H ; the absolute start-address of XDATA memory XDATALEN EQU 800H ; the length of XDATA memory in bytes.
This corresponds to the 0x0800 'Options for Target', 'Target' settings: Off-chip Xdata memory Start: 0x0000 Size: 0x0800
Thanks, Tobias
Your device might also have a bit in an SFR that controls the accessibility of the internal XRAM.
The lines you posted merely indicate that the startup file will try to clear this XRAM address range, they do not say anything about there being XRAM at all.
The device i use is the Oregano systems IP core. There is no bit to enable the XRAM. The Assembly code of the 'main.c' file shows that it accesses the XRAM at 0x0124:
5: void main(void) 6: { 7: receivedstring[0]='q'; C:0x001D 900124 MOV DPTR,#receivedstring(0x0124) C:0x0020 7471 MOV A,#0x71 C:0x0022 F0 MOVX @DPTR,A 8: a=receivedstring[0]; C:0x0023 F508 MOV a(0x08),A
And...: Yes, in the startup file, it only clears the XRAM address range. Should i add anything else here?
Have you tried leaving out the "_at_ 0x124" at the end of the extern definition ?
It is unnecessary might cause problems. Where a variable actually is located needs to be specified only once, and that was already in the original declaration of the variable.
Yes, after a Mah-Mee... i deleted the "_at_ 0x124" at the extern definition. That caused the problem. (A linker warning would be helpful..)
Thanks and regards, Tobias