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PAR(ameter) Value — Parallax Forums

PAR(ameter) Value

pjvpjv Posts: 1,903
edited 2006-05-02 05:41 in Propeller 1
Hello Chip;

Is there a reason why the Par(ameter) value passed on launching a new COG must have the two·least significant bits·cleared? I understand that main memory addresses require "long" boundaries implying zeros for those bits,·but when PAR is used for something other than an address, the LSB zeros are a bit of a pain.

As long as·the programmer is aware of the "long" boundary requirement, and properly deals with that, could a next rev of silicon have those two bits enabled? Or perhaps·there is some inherent issue that I don't understand that prevents this.

Cheers,

Peter (pjv)
·

Comments

  • cgraceycgracey Posts: 14,133
    edited 2006-05-02 05:41
    Peter,

    Yes, there is a reason for this. In the COGINIT instruction, the 'D'estination register conveys three things: which/new COG to start (4 bits), a long load address (14 bits), and a long PARameter address (14 bits). That all adds up to 32 bits. I, too, have had occasions where 16-bits would have been handy to convey via PAR. In the next generation, there is quite a bit more global memory, so the 'S'ource register will have to be used to convey some data, too. I think that in that case, where there are not such bit constraints, we could convey an 18-bit·byte address (working lsb's) for PAR.
    pjv said...
    Hello Chip;

    Is there a reason why the Par(ameter) value passed on launching a new COG must have the two·least significant bits·cleared? I understand that main memory addresses require "long" boundaries implying zeros for those bits,·but when PAR is used for something other than an address, the LSB zeros are a bit of a pain.

    As long as·the programmer is aware of the "long" boundary requirement, and properly deals with that, could a next rev of silicon have those two bits enabled? Or perhaps·there is some inherent issue that I don't understand that prevents this.

    Cheers,

    Peter (pjv)
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    Chip Gracey
    Parallax, Inc.
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