You've became a victim of misconception :)
Directive .var declares placeholder for data in atari memory at the end of code, where it's used. "mwa" does not declare any value, because it is a kind of 6502 code macro So when you write "mwa #10 j" it generates sequence of "lda #10 sta j" . It does not change value of j. ".if j > 10" always holds because you assemble your code to memory address greater than 10 :)

Ostatnio edytowany przez laoo/ng (2007-09-16 19:13:39)

"sta j" changes value in atari memory at address held in label "j". So "j" is not really a variable, but a label of (or a "pointer to") some place in memory. There is obvious difference between assigning value to label (virtually by MADS during assembling) and storing value in memory (physically by 6502 during execution of resulting program). Here you have a listing from simple example:

     1                     org $2000
     2
     3 = 0000            .var j .word
     4
     5 FFFF> 2000-2008> A9 0A        lda #10
     6 2002 8D 07 20            sta j
     7
     8                 .if j > 10
     9 2005 69 66            dta c'if'
    10                 .else
    11                     dta c'else'
    12                 .endif
    12 = 2007 00 00        J

MADS assigned to "J" value of $2007 (at the end of code) and "sta j" stores content of acumulator to memory at addres $2007. '.if' does not know anything about contents of this memory location. It checks value of label "j" which is $2007, therefore "j > 10" evaluates to true. Try to assemble it from addres 0 (org $0000) then address of "j" would be $0008 and "j > 10" would be evaluated to false and "else" path of condition would be used.

You have to distinct "metaprogramming" in assembler from "programming" on machine.

Thank you laoo/ng, it tells me a lot more about internal functioning of MADS. What i missed was clarifying some things like the problem above. It will help me to understand more and differentiate labels and variables at specific memory addresses.

Ostatnio edytowany przez Gury (2007-09-16 21:07:50)

The above 'if' will always evaluate false. TEMP1 and TEMP2 are still "pointers", not the data.
One thing that confuses you clearly, is that .IF (or IFT) is actually evaluated during COMPILATION not EXECUTION. It's a preprocessor directive, and not some macro.
It's useful for things like conditional compilation, e.g.:

  ldx array,y
  .if DEBUG_ON
  stx $20  ; so we can check in a debugger what 'routine' was called with
  .endif
  jsr routine

If DEBUG_ON is on, the STX will be included in the compiled program, if not, not.

Ostatnio edytowany przez eru (2007-09-16 21:53:41)

Gury use directive .TEST , .ENDT (.ELSE, .ELSEIF not exist)

.test .word j>#10 (value = 10)

.test .word j>10   (value from addres 10..11)

.test .byte     - ok
.test .word    - ok

.test .long       - not working
.test .dword    - not working

org $2000

.var j .word

mwa #10 j

.test .word j > #10
  jsr printf
  dta c'*** j > 10 ***',$9b,0
 
  jmp skip
.endt

  jsr printf
  dta c'*** j = 10 ***',$9b,0

skip

jmp *

.link 'stdio\printf.obx'

run $2000

Ostatnio edytowany przez tebe (2007-09-17 00:39:12)