What does ## mean in Prop-2 assembly language?

Comments

• Wuerfel_21 Posts: 4,464

  2020-05-01 22:32

  It inserts an AUGS and/or AUGD instruction before the actual instruction to allow for large immediates
• whicker Posts: 749

  2020-05-01 22:40

  It means you want a value larger than 511, at the cost of doubling the size of the instruction.
  
• JonTitus Posts: 193

  2020-05-01 22:48

  Ah, perfect. Thank you both. --Jon
• Cluso99 Posts: 18,069

  2020-05-01 23:02 edited 2020-05-01 23:09

  ## if used in the D operand (main use) then the instruction

  [label]  opcode  [#]S,##D
  

  will become 2 instructions something like

  label  AUGD    #(D>>9)            ' D[22:0] are 23-bits forwarded to D [31:9] in the next instruction
         opcode  [#]S,#(D & $1FF)   ' D[8:0] plus the forwarded D[31:9] from the previous instruction
  

  such that the AUGS instruction feeds the top 23 bits [31:9] (ie 32-9) bits which gets fed forward to be used in the next "S" instruction when it executes. Note that addresssing is only 20 bits, so if it's an address in the next instruction, only the bits [19:0} will be forwarded. This allows for the following instruction to be able to load a register with a full 32 bit value. The following instruction provides the bits [8:0] (ie 9 lower bits) which are combined with those forwarded by the previous AUGS instruction.
  
  AUGD provides a similar method for the D bits in the following instruction.
• evanh Posts: 15,187

  2020-05-01 23:08

  There is very terse pasm2 description in "Instructions.txt" of the Pnut zip download. Should be some help - https://forums.parallax.com/discussion/171196/pnut-spin2-latest-version-v34r
  
  
• Rayman Posts: 13,860

  2020-05-01 23:26

  You picked a great time to learn PASM!
  In the past, it was a pain to use any numeric value > 511
  Now, it's no problem! Just use ## and the assembler will magically make it all work.
  (It just adds an extra instruction)