How does OFFSCRPT work?
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How does OFFSCRPT work?
CALCnet Tournament-38%


deviantArt
souvik1997 wrote:
How does OFFSCRPT work?
I've moved this into the z80 ASM programming subforum for the sake of consistency.

So, the OFFSCRPT is an appvar that contains executable code. The code within it, if it exists, is run every time the calculator turns off under the TI-OS's control (although not necessarily if a program or shell turns the calculator off, of course). The contents of the OFFSCRPT appvar are copied to memory starting at $8001, executed, and cleared. For example, Doors CS can create the following OFFSCRPT appvar that will install a GetkeyHook to launch Doors CS once the calculator turns on again:


Code:
OffScrptCode:
.relocate $8001
  bit 4,(IY+apdFlags)
  ret nz
  ld hl,MyAppName
  rst 20h
  bcall(_FindApp)
  ret c
  dec a      ;this is on page 2
  ld hl,MyGetKeyHook
  bcall(_EnablegetKeyHook)
  ;set 0,(iy+34h)
  ret
MyAppName:
  .db AppObj,"DoorsCS7"
  ret
.endrelocate
OffScrptCodeEnd:


Installing the OFFSCRPT involves creating the Appvar, of course, as well as setting bit 1 of (iy+33h) to indicate that an OFFSCRPT Appvar is installed. To uninstall it, delete the Appvar and reset 1, (iy+33h), although you can also get away with either only deleting the variable or only resetting the flag. The following code installs an OFFSCRPT if a=1, or removes it if a=0.


Code:
            or a
            jr z,RemoveOffScript
CreateOFFSCRIPT:
            ld hl,OffScriptName
            rst 20h
            bcall(_chkfindsym)
            jr nc,OffScrptCont
            ld hl,OffScrptCodeEnd-OffScrptCode
            bcall(_enoughmem)
            jr c,OffScrptCont
            ex de,hl
            push hl
               bcall(_createappvar)
               inc de
               inc de
               ld hl,OffScrptCode
               pop bc
            ldir
            set 1,(iy+33h)
            jr OffScrptCont
RemoveOFFSCRIPT:
            ld hl,OffScriptName
            rst 20h
            bcall(_chkfindsym)
            bcallnc(_delvararc)
OffScrptCont:


There's a similar system called an ONSCRPT that is run when the calculator first powers on rather than when it's about to power off, but we've found it to be very unreliable and unpredictable.
Thanks!
CALCnet Tournament-38%


deviantArt
souvik1997 wrote:
Thanks!
Sure thing, and please feel free to let me know if you have additional questions. May I ask what this is for?
I was wondering how TI's Startup App worked.
CALCnet Tournament-38%


deviantArt
souvik1997 wrote:
I was wondering how TI's Startup App worked.
Ah, that makes sense. Chances are that it's actually only 2KB or 3KB of actual code in the app, just enough to launch the parser or copy a picture to the graphscreen, plus of course the menu stuff.
  
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