[A83] Re: interrupt with shutdown

[Prev][Next][Index][Thread]

[A83] Re: interrupt with shutdown


I just tested it out and a DI at the start of an interrupt routine is not
necessary, at least not on the TI83-.

I also changed a few things in your shutdown code. A short explanation...

The apd counter should also be reset if you press 2nd+On.

Then, what actually happens during the shutdown code is this. When you out
1 to port 3, that means you only enable on-key interrupts and disable all
other sorts of interrupts, like the timer interrupt (the one at 120/130
Hz). By outing 1 you also turn off the lcd. Then you enable interrupts
(EI) and put the calc in low power mode waiting for an interrupt (HALT),
which will be an on-key interrupt as since that's the only one we allowed.
So when you turn the calc back on, an interrupt occurs and thus your
interrupt routine is called. That interrupt returns to the address
following the HALT, so that's the right place to put all sorts of things
you want to do before giving all control back to the TIOS (e.g. display a
welcome message). The RET after the HALT will return to the place where
the original interrupt occured.

Finally, at the end of your routine you had this code:

1:    exx
2:    ex af,af'
3:    call $0038
4:    ei
5:    ret

Lines 3,4,5 can be replaced by JP $0038, because the standard interrupt
routine has an EI \ RET, so you don't have to repeat that. Then, you don't
need to exchange the shadow registers, because the code at $0038
immediately exchanges them back. All 5 lines can thus be replaced by:

    jp    $003A


Commented lines can be removed, others should remain.


> From: "SUCKER from the old days" <sucker_pvn@hotmail.com>
>

[..code skipped..]

> interrupt_start:
> ;---------------
>

; > di

> ex af,af'
> exx
>          ld a,($800A)               ; check for apd
>          cp $11                     ;
>          jr nc,resume           ;
> shutdown:
> res shift2nd,(iy+shiftflags)
>          ld a,$74                   ; reset apd counter
>          ld ($800A),a               ;

; I'm not sure whether these two lines are necessary, but honestly I don't
know.
; The docs say it turns the LCD ON and that's not what we want at this
point.

> ld a,8
> out (3),a

> ld a,1
> out (3),a

    exx
    ex    af,af'

> ei
> halt


; here you can put the code to ask a password.

    ret

; > ; here I forgot something
; >       di
; > jr stop

> resume:
> bit shift2nd,(iy+shiftflags)
> jr z,stop
> in a,(3)
> and 8
> jr z,shutdown
> stop:

    jp    003Ah

; > exx
; > ex af,af'
; > call $0038
; > ei
; > ret

>
>
> ;------------
> interrupt_end:
>
> text1: .db "Interrupt",0
> text2: .db "Disabled",0
> text3: .db "Enabled",0
> prog: .db 6,"ZINT",0
> current: .db 0
> .end
> END
Follow-Ups: