Posted By
soft-ice
on 2020-12-12
06:00:59
|  Calling 'RUN' from Machine Code
Hi all,
Does one of you know how to call 'RUN' from machine code? You would think it is as simple as "JMP $8BBC" or "JSR $8BBC", but unfortunately this issues a "UNDEF'D STATEMENT ERROR". Also doing a "SYS 35772" instead of "RUN" gives the same problem.
Possibly some constants need to be set first?
Thanks for you advice.
Best,
"Soft-ice"
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Posted By
Basman
on 2020-12-12
13:09:41
| Re: Calling 'RUN' from Machine Code
Hello, I'm using:
CLI
JMP $8bdc
Also, see if you need to alter the Basic pointers beforehand.
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Posted By
Csabo
on 2020-12-12
17:04:22
| Re: Calling 'RUN' from Machine Code
It can be a little hard to find, but we do have this exact piece of info in our Knowledge Base  Here it is!
RUN Command
From that page:
Machine Language
To perform the equivalent of the RUN command, use this code:
JSR $8BBE
JMP $8BDC
As Basman mentioned, the BASIC pointers ($2B/$2C) have to be set (they have to point to a valid BASIC program).
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Posted By
Soft-ice
on 2020-12-12
17:46:04
| Re: Calling 'RUN' from Machine Code
Thanks to you both!
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Posted By
Soft-ice
on 2020-12-13
05:38:21
| Re: Calling 'RUN' from Machine Code
It works now! Thanks.
Out of curiosity: Any idea why it is so that JMP $8bbc does not work? After all, the "RUN" command links to 8bbc, so naively I would think that sys dec("8bbc") is equivalent to "RUN"? What is the reason that it does not work?
Soft-ice
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Posted By
Csabo
on 2020-12-13
07:22:21
| Re: Calling 'RUN' from Machine Code
It's true that the jump table for the RUN BASIC command ends up at $8BBC. However, if you check the ROM at that location, you can see that it starts with a BNE. That branch only works (or makes sense) when it's the BASIC interpreter that goes there.
These two calls "simulate" what should happen, the branch does not occur (so we end up on $8BBE, that's what the first JSR is), and so on.
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Posted By
soft-ice
on 2020-12-13
07:36:12
| Re: Calling 'RUN' from Machine Code
Thanks for the clarification! Very helpful.
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