Re: A82: Re: Re: Assembly-82 Digest V1 #702

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Re: A82: Re: Re: Assembly-82 Digest V1 #702


>Boulderdash uses the memory before GRAPH_MEM for temporary storage during
>the game. This area contains the dTbl value and other information like 
>that.
>The value you mention is in the middkle of the area used by boulder dash so
>it is likely that other values are altered too.
>
>I had a look at the boulderdash source code, but could find any problems.
>The area which is modified is backed up before it is altered and restored
>before you exit the game. Since you have to start playing for the problem 
>to
>occur, there has to be a line of code in the game which modifes the last
>half of TEXT_MEM.
>
>Dines

  Actually the problem was so blatantly obvious that I feel I should 
probably smack myself. Here's an ASM intelligence test:

BD startup code:

         ld       de,GRAPH_MEM-192    ;Address of memory to restore
         ld       hl,TEXT_MEM2      ;Address of save buffer
         ld       bc,128           ;Number of bytes to copy
         ldir

         ld       de,GRAPH_MEM-64    ;Address of memory to restore
         ld       hl,TEXT_MEM+64      ;Address of save buffer
         ld       bc,64           ;Number of bytes to copy
         ldir
         ld (iy+13),0  ;No scrolling Text
         res 1,(iy+$0D)
         ...
  Hehe. Oops :)

   In case you didn't catch it, my hl and de registers are switched causing 
the data in TEXT_MEM2 and TEXT_MEM to be copied to GRAPH_MEM-192, not the 
other way around. So the TIOS data was not actually getting backed up.
    At least it's easy to fix :)
   Sam


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