Virtual 6502 — Another Update

A few new features for the 6502 online disassembler.

Another update to the “virtual 6502” disassembler, which has obtained a few new features regarding symbol tables:

• Addresses immediately follwing a declared symbol will be translated to a labeled “+1” address (optionally). This may be useful with any code setting up pointers, etc, where only the low-address is declared as a symbol (as is often the case with zero-page system addresses.)
  E.g.,

  Object code (start address 0x0800):
  
   A9 01 85 B8 A9 40 85 B9
  
  Symbol table:
  
   SETPTR   = $0800
   POINTER  = $B8
  
  Disassembly:
  							 * = $0800
   0800   A9 01      SETPTR    LDA #$01
   0802   85 B8                STA POINTER
   0804   A9 40                LDA #$40
   0806   85 B9                STA POINTER+1
  							 .END

• Symbols may be optionally declared specifically for write access only by a “w” suffix (case-insensitive). Think of the Atari VCS (AKA Atari 2600) and TIA read and write registers sharing the same address.
  (The assembler ignores such a suffix in order to provide compatibility with such symbol tables.)
  E.g.,

  CXP0FB = $02   ;read register
  WSYNC  = $02 w ;write access only

• Predefined symbol tables for the C64, the PET 2001, the Atari VCS, and the BBC Micro/Acorn may be loaded directly from the UI.
• The disassembler now supports .DATA pseudo instruction for its symbol tables to declare an address or a range of addresses as data to be excluded from the disassembly (".BYTE" pseudo instructions will be added instead.)
  E.g.,

  .DATA $2040           ;exclude a single address
  .DATA $2040 ... $240F ;exclude range $2040 … $240F (inclusive)
  .DATA $2040, $240F    ;as above
  .DATA D1 ... D1+4     ;expressions are allowed

  A comment with a binary representation of the respective byte (e.g., “;%01110101”) will be added to any verbose output format, in order to help identifying sprites and similar patterns.

  This should be a useful for drilling down on some code: just keep adding “.DATA” statements to your symbol table as you identify a data section and keep on disassembling.
  (Again, such a DATA pseudo-instruction is ignored by the assembler to assure compatibility.)

Moreover, all the “virtual 6502” apps now support input and output in “&…” hex notion to comfort those who were tragically mislead by the BBC (while MOS made it quite clear that is “$…”). ;-)
(Seriously, I’ve really the highest respect for the BBC Micro, which was an enormous achievement.)

By this, the disassembler looks much like feature-complete.