Re: [stella] Thrust incompatibility? (Possibly illegal opcodes)

Subject: Re: [stella] Thrust incompatibility? (Possibly illegal opcodes)
From: "Thomas Jentzsch" <tjentzsch@xxxxxx>
Date: Fri, 2 Feb 2001 08:54:56 +0100
Mark De Smet wrote:
> I am most puzzled by the sears video arcade 2 not working, because I
> thought the sears models were produced by atari and just rebranded.
> Thomas, do you know what could happen to cause the above problems?  Can it
> be linked to an illegal opcode?

No, there aren't any illegal opcodes in my kernel (just very close timings) or the thrust routine.
Here is the thrusting code:

    lda     INPT0               ; 3         booster grip trigger
    ora     INPT1               ; 3         booster grip booster
    bmi     .doThrust           ; 2³

    lda     ShipPosYlo          ; 3         shield activated?
    and     #[SHIELD_ON]        ; 2
    beq     .noShield           ; 2³         no, skip
    lda     INPT4               ; 3         fire button pressed?
    bpl     .doThrust           ; 2³         yes, thrust
    bmi     .noThrust           ; 2³         no, skip

    lda     SWCHA               ; 4
    and     #JOYUPMASK          ; 2
    bne     .noThrust           ; 2³


I guess the 2800 problem has something to do with the booster grip code.
Maybe someone will write an emulator which simulates all incompatiblities, then i could try to change my code a little bit. :-)

Thomas Jentzsch         | *** Every bit is sacred ! ***
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