hi,


I see yet another ways:
1) PC always see parameters/variables at fixed absolute addresses. PC may even call them not "addresses" but "parameters` numbers". Nevertheless, inside MCU they are placed as continuous array with dispacement which value may be different from modification/upgrade. Anyway, MCU knows this displacement and may easy calculate requisite absolute address.
2) MCU reserves upto 256 bytes in code segment for relocation table: one byte for each parameter number. These bytes define real absolute addresses of requisite parameters` numbers in current modification/upgrade. So:
2a) either MCU does relocation replacement itself;
2b) either PC asks for this table as first step and then uses it to get absolute address.

By the way, method you described, is dangerous. I hope you have implemented a kind of sanity check when PC asks write to absolute RAM location. Otherwise due some network malfunction it may destroy a wrong variable or, for example, stack content.

Well, first of all, there are no commands like
anl r1,#03h
orl r1,#Scramble
...but I understand that it is just a typpo (should be anl 1,#03h etc).
What I wish to say: good example. As for me, so with such strong requirements you shown us, I would preffer to use segments anyway, something like:

Scramble_addr	EQU	0x30
SrcBuf_addr	EQU	0x40
DstBuf_addr	EQU	0x60

		ISEG	AT Scramble_addr
Scramble:	DS	4

		ISEG	AT SrcBuf_addr
SrcBuf:		DS	32

		ISEG	AT DstBuf_addr
DstBuf:		DS	32

;...
;
;at start, r0 contains pointer to SrcBuf
;          b  contains message length
   mov   r1,0
   anl   1,#03h          ;first, calculate pointer into Scramble
   orl   1,#Scramble_addr
Loop:
   mov   a,@r0            ;get data from SrcBuf
   xrl   a,@r1            ;perform scramble
   xrl   0,#(SrcBuf_addr XOR DstBuf_addr)     ;get pointer to DstBuf
   mov   @r0,a            ;store scrambled data
   xrl   0,#(SrcBuf_addr XOR DstBuf_addr)     ;restore pointer to SrcBuf
   inc   r1               ;increment Scramble pointer
   anl   1,#0FBh          ;wrap around Scramble pointer
   inc   r0               ;increment SrcBuf pointer
   anl   0,#0DFh          ;wrap around SrcBuf pointer
   djnz  b,loop

For my point of view, this way helps locator to check memory usage and always gives me a chance to see warning/error if some other variables will overrun or are placed wrong. In your example, if you by ocasion define a variable inside any buffer then you will not be noticed about that during compiling. In my case, when all variables are defined with Keil assembler requirements, it is much more safe.


Agreed.

Regards,
Oleg