Instruction Prefix EEEE -> Prefix condition PPPP ?

I've never used the Propeller and I've been reading the P2 Documentation and Instructions (v18) for the first time today.

Getting rid of CCCC to avoid confusion with carry seems a good idea to me but EEEE doesn't suggest a condition that is prefixed.

Comments

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  • TonyB wrote: »
    I've never used the Propeller and I've been reading the P2 Documentation and Instructions (v18) for the first time today.

    Getting rid of CCCC to avoid confusion with carry seems a good idea to me but EEEE doesn't suggest a condition that is prefixed.

    I agree, but what to call it, then?

    I used EEEE for 'execution condition'.
  • jmgjmg Posts: 10,608
    edited April 21 Vote Up0Vote Down
    Prefix operation is an Assembler design detail, not so much something embedded into the opcode.
    Using CCCC or EEEE or PPPP alerts that there are 4 bits in the field, but dos not try to identify individual bits.

    Another name could be COND, also 4 char/bits, but tag is now a real word, closer to assembler use.

    Whatever is used, is going to need some expansion explanation.
    I see Chip uses Instruction Prefix later in the Docs

    Adding a header tag to the encoding column may be enough ?
    EEEE = Instruction Prefix, see line 385..

    or

    COND = Conditional Instruction Prefix, see line 385..

    or

    PRFX = Conditional Instruction Prefix, see line 385..

    Choose the easiest to read/scan ?
  • PPPP = Prefix condition
    or simply
    PPPP = Prefix

    Putting the conditions are the start of the line will be strange at first for a lot of newcomers used to other microprocessors. Moving the bits formerly known as condition codes to the msb's helps reinforces the idea that they are prefixes. P for prefix ...
  • jmgjmg Posts: 10,608
    TonyB wrote: »
    PPPP = Prefix condition
    or simply
    PPPP = Prefix

    Putting the conditions are the start of the line will be strange at first for a lot of newcomers used to other microprocessors. Moving the bits formerly known as condition codes to the msb's helps reinforces the idea that they are prefixes. P for prefix ...

    Maybe, but the Conditional aspect is more important than the Prefix one, P alone makes it sound like some mandatory prefix ?
    Most assembler lines have no prefix at all (encoded by assembler with COND = 1111)

  • Lower case c for one / upper case C for the other?
  • Tubular wrote: »
    Lower case c for one / upper case C for the other?

    That's a good idea.
  • EEEE is good. It's perfectly clear after a quick check, no more repeated confusion. Much better than the Prop1 for sure. Leave it alone.
    The Prisoner's Dilemma, in english - "Selfishness beats altruism within groups. Altruistic groups beat selfish groups." - Quoted part from 2007, D.S Wilson/E.O Wilson.
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