Oakland CPM Archive/oakcpm.iso/sigm/vol115/pseudo.doc

Text File | 1985-02-10 | 8.0 KB | 263 lines

               -- THE ART OF THE PSEUDO RUN --
                        Ron Winter     3/13/83
             I⌠á i≤á possiblσ t∩ singlσ ste≡ ßá z8░á s-10░ ì
        systeφá iεá softwarσ withou⌠ decodinτá thσá `nextº ì
        instruction. All that is required is a 74ls74.
             Thσá z8░ ª ╔ assumσ thσ 8080¼á 808╡ allo≈ onσ ì
        instructioεá afte≥á aεá E╔ t∩á occu≥á eveεá iµá aε ì
        interrup⌠á i≤ pending«á Thi≤ i≤ t∩ allo≈ aε RE╘ iε ì
        aεá interrup⌠á handle≥ so tha⌠ ßá stacδá runawa∙ ì
        doesn't occur under a barrage of interrupts.
             Le⌠á u≤ finΣ aε instructioε t∩ placσá betweeε ì
        thσ E╔ anΣ RE╘ tha⌠ wil∞ generatσ aε interrup⌠ tw∩ ì
        instruction≤á late≥ tha⌠ preserve≤á al∞á register≤ ì
        fo≥ ou≥ interrup⌠ handler«á Conside≥ thσ followinτ ì
        circuit.

         ________________________________________________
        |                                                |
        |                              pu  enable-p      |
        |                            10|     |           |
        |                           ___o___  |  __       |
        |           _________    12|   S   |9|-|  \      |
        |         4|         |  pu-|D     Q|---+   |o-   |
        |       ___o___      |     | 1/2   |   |__/  |   |
        |     2|   S   |5    |   11| ls74 _|8        o   |
        |     _|D     Q|-----------|> (b) Q|o-nc    / \  |
        | _  | |  1/2  |     |     |   R   |       o   o |
        | M1 |3| ls74 _|6    |     |___o___|       |   | |
        | ==>--|> (a) Q|o_   |       13|          VIn NMI|
        | 44 | |   R   |  |  |_________|                 |
        |    | |___o___|  |            |                 |
        |    |    1|pu    |            |                 |
        |    |____________|            ^                 |
        |                             arm-n              |
        |                          [OUT (XX),A]          |
        |------------------------------------------------|

             WitΦá thσ aiΣ oµ an∙ por⌠ (XX⌐ tha⌠á onσá caε ì
        safel∙ writσ t∩ anΣ ge⌠ ß lo≈ goinτ pulsσá iε theì
        `write' window, we have the follwing sequence.

        1«á witΦá n∩á interrup⌠ pendinτ iεá ou≥á interrup⌠ ì
            handler we do an EI.

        2«á wσá nex⌠ d∩ OU╘ (XX),┴ anΣ Qß goe≤á high¼á QΓ ì
            goes low.

        3«á wσ d∩ aε RE╘ anΣ oε thσ trailinτ edgσ oµá M1¼ ì
            Qa goes low, Qb no change.

        4«á Nex⌠ pπ begin≤ anΣ oε it≤ M▒ enΣ Qß goe≤ higΦ ì
            clocking Qb to high causing an interrupt.

            Thi≤á leave≤ thσ wonderfu∞ dilemnß oµ wha⌠ t∩ ì
        do with it!è

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             Le⌠á mσ describσ wha⌠ ╔ do«á ┴ smal∞á prograφ ì
        sets up the system as follows.

        1«á   LoaΣ ß jum≡ vecto≥ t∩ ß safσ placσ iε (high⌐ ì
        memor∙ a⌠ rst╢ (30hex⌐ anΣ wirσ outpu⌠ oµá circui⌠ ì
        t∩á VI╢á (S-10░ piε 10)«á Notσ circui⌠á shoulΣá bσ ì
        disabled at this time.

        2«á   A⌠ thσ vector¼ writσ aε interrup⌠ handle≥ t∩ ì
        do whatever you please!

        3«á   Displa∙á somethinτ oε thσ screeε t∩á signif∙ ì
        tha⌠ thσ circui⌠ i≤ availablσ anΣ exi⌠ bacδ t∩ thσ ì
        system.

        4«   Executσ tha⌠ whicΦ onσ wishe≤ t∩ stud∙ anΣ a⌠ ì
        an∙á convenien⌠á timσ enablσ ßá VI6«á ┴á momentar∙ ì
        switch will work.

        5.   Voila, I am in my interrupt handler.


             T∩á makσ lifσ easie≥ le⌠ u≤ sa∙ thσ interrup⌠ ì
        handle≥áá doe≤á thσá following«áá I⌠áá save≤áá al∞ ì
        registers¼á save≤á thσá curren⌠á curso≥á position¼ ì
        paint≤á ß prett∙ displa∙ oε somσ protecteΣ par⌠ oµ ì
        thσ screeε anΣ poll≤ thσ keyboarΣ fo≥ input« Iµ n∩ ì
        ke∙ theε restorσ cursor¼á restorσ register≤ anΣ d∩ ì
        EI, OUT (XX),A and RET.
             S∩á unti∞á ß ke∙ i≤ strucδá durinτá interrup⌠ ì
        handle≥ thσ processo≥ `pseud∩ runs'« Thσ effectivσ ì
        speeΣ i≤ thσ timσ i⌠ take≤ t∩ ruε one'≤á interrup⌠ ì
        handler¼á s∩á thσ quicke≥ anΣ dirtie≥ thσ codσ thσ ì
        better!
             Notσá oµ warning«á I⌠ i≤ generall∙á safe≥á t∩ ì
        surrounΣá one'≤á BIO╙ I╧ hardwarσá dependen⌠á codσ ì
        witΦá D╔ anΣ E╔ t∩ preven⌠ `termina∞ confusionº a⌠ ì
        one'≤ hardwareí Thu≤ onσ shoulΣ cop∙ one'≤ I╧ codσ ì
        inlinσ int∩ thσ interrup⌠ handler«á Thi≤ wil∞ als∩ ì
        save time (less system jumps etc.)
             T∩á makσá lifσ eveεá easier¼á structurσá you≥ ì
        interrup⌠ `monitorº t∩ enablσ futurσ addition≤ anΣ ì
        options. Currently mine does the following:

             Oεá firs⌠á entr∙ iµ n∩á ke∙á i≤á struck¼á usσ ì
        `lastºá ke∙á whicΦ i≤ prese⌠ t∩ <space╛ t∩á enablσ ì
        singlσ ste≡ witΦ pause«á Tha⌠ is¼á iµ n∩ ke∙á theε ì
        pol∞ again«á Iµ ke∙ theε test« ┴ <ret╛ switche≤ t∩ ì
        `pseud∩ runº b∙ storinτ <ret╛ a⌠ `las⌠ key'« ┴ <B╛ ì
        prompt≤ fo≥ aε addres≤ anΣ set≤ ß breakpoin⌠ (somσ ì
        othe≥ rs⌠ instruction¼ save≤ thσ bytσ overwritten¼ ì
        anΣá thσá vecto≥ a⌠ `otherº rs⌠ restore≤á origina∞ ì
        bytσá anΣá theε enter≤ codσ fo≥á `monitorºá havinτ ìè

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        lef⌠ ß <space╛ a⌠ `lastº key«á Notσ thi≤ enable≤ ß ì
        full speed run.á
             Iµá yo⌡á havσ availablσ anothe≥ por⌠ yo⌡á caε ì
        writσ t∩ tha⌠ caε latcΦ ß leve∞ yo⌡ caε ì
        enable/disablσ thσ `stepperº unde≥ softwarσ ì
        controlí ╔ do¼ s∩ m∙ initia∞ codσ disable≤ i⌠ anΣ ì
        request≤ ß breakpoin⌠ theε jus⌠ exit≤ t∩ thσ ì
        system« N∩ switche≤ necessary¼ a≤ ß matte≥ oµ fac⌠ ì
        i⌠ jus⌠ sit≤ iε m∙ systeφ a≤ jus⌠ anothe≥ utility« ì
        Wheε ╔ wisΦ t∩ usσ i⌠ ╔ jus⌠ ruε i⌠ likσ an∙ othe≥ ì
        transien⌠ program.
            Somσ suggesteΣ option≤ &/o≥ addition≤ tha⌠ onσ ì
        caε implimen⌠ iε one'≤ onσ persona∞ `pseud∩ ì
        machineº o≥ emulato≥ iµ yo⌡ will.
        1«á  optioε t∩ modif∙ registe≥ a⌠ an∙ time  (ver∙ ì
             easy).
        2«   displa∙ anΣ savσ onl∙ wha⌠ onσ need≤ t∩ speeΣ ì
             up the emulation (not so easy).
        3«áá ruεá unti∞á certaiεá opcodes¼á RE╘á family¼ ì
             etc. (not to hard).
        4«á  ruεá unti∞ an∙ registe≥  equal≤á somσá valuσ ì
             (very easy).
        5.   set any number of breakpoints (easy).

             So far I have only implimented 3.

             Final warnings and notes:
        I⌠á i≤á ß ne≈ experiencσ t∩ contro∞ ß prograφá anΣ ì
        interac⌠á witΦ i⌠ simultaneousl∙ a⌠á onσá console¼ ì
        especiall∙á program≤ tha⌠ d∩ ß lo⌠ oµ consolσá IO« ì
        Thσá curso≥á wil∞ dancσ froφ targe⌠ t∩ contro∞á s∩ ì
        fas⌠á yo⌡á wil∞ havσ ß harΣá timσá decidinτá whicΦ ì
        prograφá yo⌡á arσ controllingíá ╔ usuall∙á se⌠á m∙ ì
        breakpoint≤á arounΣ ß sectioε oµ I╧ unles≤ tha⌠ i≤ ì
        wha⌠ ╔ wisΦ t∩ study« Iµ yo⌡ havσ aε extrß consolσ ì
        i⌠á coulΣ bσ thσ `emulatorº I╧ anΣ theε yo⌡á woulΣ ì
        reall∙ havσ ß nicσ setup«
             ╔ havσ drawε aε optioε fo≥ NM╔ interrup⌠ tha⌠ ì
        caε bσ implimenteΣ iµ desired« No≈ one'≤ vecto≥ i≤ ì
        a⌠á 66he° anΣ onσ caε blithel∙ singlσ ste≡ througΦ ì
        codσ tha⌠ i≤ `protectedº froφ interrupts« Onσ mus⌠ ì
        onl∙á observσ thσ statσ oµ thσ interrup⌠ flaτá anΣ ì
        restorσ i⌠ a⌠ thσ enΣ oµ thσ routine¼á tha⌠ i≤á oε ì
        thσ z8░ changσ E╔ OU╘ (XX),┴ anΣ RE╘ t∩ OU╘ (XX),┴ ì
        anΣ RET╬.
             S∩ tha⌠ i≤ wha⌠ ß 74ls7┤ caε d∩ witΦ ß littlσ ì
        softwarσá iεá you≥ system«á Wh∩á ha≤á thσá fastes⌠ ì
        disassemble≥á (opcodσá t∩á mnemoniπá algorithm⌐á ╔ ì
        wonder?








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