96 lines
4.1 KiB
Erlang
96 lines
4.1 KiB
Erlang
Combining Applesoft with Assembly
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Inspired by an article in Nibble
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==================================
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The latewt issue of Nibble Magazine ,October '85, has a very interesting
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article in it regarding the combination of Applesoft and Assembly into one
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Applesoft file. I am extremely upset that I didn't think of this before! It
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really is an interesting trick! If you have read the article and had trouble
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using the instructions provide there or if you did not see the article, then
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please read on....
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When an Applesoft (referred to as A/S from here on) pvogram is loaded into
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memory either as you program or loaded from disk, the length of the A/S program
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is held in a specific memory location: AF.B0. To add some additional assembly
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to the program, you merely move the assembly code in memory down to the location
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right after whatever is stored in AF.B0. For example:
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1. The A/S program is loaded first.
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2. Enter monitor by using CALL -151.
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3. Type AF.B0 anl read the last address used by the A/S program.
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4. Remember that the lo-byte is used first (AF) and that the hi-byte (B0) is
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last. If you see this:
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AF.B0-18 08
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this means that the last address used by the A/S program is 0818.
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5. The SAVE command in A/S uses this location as a pointer to the last
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aldress in the program and saves everything from 0800 upward to the
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address held at AF.B0.
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6. To add the assembly program to an A/S file, you would BLOAD the assembly
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portion just past the end of the A/S program.
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BLOAD ULTIMA CHEAT OBJ.,A$0819
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7. Thys will put the assembly right on Top of the A/S program!
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8. OK but how do I save it??? Easy! Simply add the length of the assembly
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program to the address at AF.B0 anl the change the address at AF.B0 to
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reflect the longer length.
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0818 Address found at AF.B0
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+2200 Length of the assembly pgm.
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-----
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2A18 Address to put at AF.B0!
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CALL -151warm entry to A/S)
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]SAVE ROUTINE
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=======================================
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PROBLEMS AND DIFFICULTIES THAT HAPPEN
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=======================================
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Of course, it is necessary to do one of two things in order to make aall this
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work. Either make your assembly code relocatable (which you should do in any
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case) or include a memory move to relocate t`g assembly at the proper address
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once it has loaded. Here is a fool proof memory move in A/S:
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10 POKE 66,[DESTINATION-LO]:POKE 67,[DESTINATION-HI]
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20 POKE 60,[START-LO]: POKE 61, [START-HI]
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30 POKE 62,[END-LO]: POKE 63,[END- HI]
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40 POKE 71,0 [SET THE Y-REGISTER TO 0. IT IS USED AS AN INDEX BY THE MOVE
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ROUTINE THAT WE WILL CALL NEXT]
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50 POKE 58,44: POKE 59,2%4 [THIS ESTABLISHES THE MOVE ROUTINE POINTERS]
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60 CALL -327 [THIS IS THE ACTUAL MOVE ROUTINE]
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If you do not understand the above, simply use it as is and everything will
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work find. Of course, you will have to know the addresses but that is done as
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explained above.
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One problem that you WILL encounter is related to the HIRES PAGE 1. Lets say
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that you have a program that you want to run and then it is to display a hires
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picture on HIRES 1. Since our A/S programs start at 0800 and a hires picture
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length is $1FF8 or as is more popularily accepted (DAMMIT IT IS WRONG AND YOU
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WASTE ONE WHOLE SECTOR OF DISK SPACE DOING THAT) $2000, if you add $0800+$2000
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the answer is $2800! Since HIRES 1 starts at $2000 you will obviously be
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overwritting HIRES 1 and the results is GARBAGE! In a case like this, go ahead
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and waste some disk space and change AF.B0 to $3FF8 so that when you save the
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A/S program you are saving the entire HIRES 1 along with it.
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======================================
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If you have problems doing this, I will be delighted to assist! Leave me a
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message on the Rebel Alliance Pro System (leave it in feedback and Tracker will
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get it to me) at...
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206-584-6900
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This is a 10meg no hangup after one download kixass system so call it
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anyway!!!
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See you Later.... Hoe Hopper
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