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New P2 Silicon Observations



  • Right?
  • kwinnkwinn Posts: 8,697
    potatohead wrote: »

    Not sure, but I was under the impression that it had something to do with byte/long alignment between hub and cog execution.
  • potatoheadpotatohead Posts: 10,253
    edited 2018-11-19 21:33
    Oh that was in response to cool 6809 stuff.

    Yes, as I remember bytes are the common denominator. With that encoding, there is a quick computation done in COG or HUB, allowing code to run either way.

    Seems odd when looking at other chips. Makes sense on the P2 and the different addressing spaces.

    Can't find the thread on mobile... but, it may be just a shift for the COG, or in VERILOG, taking the upper bits only. It is an add for the HUB.

  • evanhevanh Posts: 15,161
    __red__ wrote: »
    ... so it is true that the actual **coded instruction** is still encoded in bytes but its assembly analog is written in longs?
    Yes. Physically it is whole 32-bit registers, so it's the byte addressing of code that is hardware emulated by cogexec mode. Probably needs some documenting beyond the forum. Can Google Docs do drawings?

    (and the next location of code that should execute after a JMP is (encoded value/4)-1?
    Not sure how to read that, but PC-relative is with respect to the instruction following the branch. ie: Program counter is already incremented and next instruction is fetched by the time the branch is executing, so the distance to jump is taken from that.

  • evanhevanh Posts: 15,161
    edited 2018-12-06 10:52
    Might have the other piece you were asking for, after having just pondered the addressing modes a little further in another topic -
    '+++++++++++++++++++++++++++++++++++++++++   orgf $018
    		loc     ptra, #palette     '   $0005c
    		loc     ptra, #@palette    '   $00178
    		loc     ptra, #palette     '   $00054
    		loc     ptra, #\palette    '   $00018
    		loc     ptra, #\@palette   '   $00060
    		mov     ptra, #palette     '   $018
    		mov     ptra, ##palette    '   $00018
    		mov     ptra, ##@palette   '   $00060
    orgf  $018
    palette		long    $12345678

    EDIT: The $178 address, like previous case, is way wrong:

    EDIT2: More learning and clarification here -

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