I see now that it is actually 7 bytes The first 3 bytes jump to F991 which is the location in ram with the code to turn the OptRom on. That returns to the next 3 bytes which call to the OptRom routine. OptRom exits and the last byte is a RET.
I have it working right now where I just poke the 7 bytes into the upper end of ALTLCD and then call it. I was just thinking that part of the OptRom initialization could push those 7 bytes somewhere in ram that wouldn't be changed. That would allow just a simple EXEC statement in basic to fire off the code. I realize that may not be realistic but I thought I would research it. Kurt On Wed, Sep 11, 2019, at 8:01 AM, Stephen Adolph wrote: > how permanently protected does the 6 byte hole need to be? > presume the RAM must contain opcodes and not just data? > a commonly used place is "Hayash"...thats 6 bytes > > > > On Wed, Sep 11, 2019 at 10:49 AM Kurt McCullum <[email protected]> wrote: >> __ >> Got the code working properly but this leads to another question. I am in >> search of 6 bytes of RAM. I used the same idea behind TS-DOS when the DOS-ON >> feature is used. That inserts 6 bytes of code that calls the OptRom ON >> routine and then jumps to the specific section of the Option ROM. When that >> routine is done, it calls the OptRom OFF routine and returns. This is really >> clean and only requires one EXEC statement in Basic to work. But it does >> require the 6 bytes of RAM. I'm looking through the technical documents >> right now to see if I can find a slice but I thought I would ask in case >> someone may know of a specific area I could use. >> >> Kurt >> >> On Tue, Sep 10, 2019, at 1:07 PM, Kurt McCullum wrote: >>> Thanks John, >>> >>> You are correct. It appears to be a stack issue. I've got the initial error >>> resolved but I've still got to do a little more work. Appreciate the >>> insights. >>> >>> Kurt >>> >>> On Tue, Sep 10, 2019, at 12:18 PM, John R. Hogerhuis wrote: >>>> Seems like you've embedded code in OptROM that you copy to ALT-LCD. >>>> >>>> When you say "the cold start recovery routine of TS-DOS" do you mean the >>>> NEC POKE and EXEC to activate TS-DOS? >>>> >>>> If so it seems your only trigger to do the LINE install is the BASIC ROM's >>>> OptROM install EXEC routine. So whenever the ROM installs, it will fill in >>>> your code into ALT-LCD. >>>> >>>> I can't think of anything that you would have to do different than >>>> whatever TS-DOS does. >>>> >>>> I suspect some stack imbalance, clobbered registers or clobbered RAM >>>> variables. >>>> >>>> -- John. >>> >>
