That protection has also been used for Moon Patrol, please refer to that topic for info (in French only): <a href="http://www.hackzapple.com/phpBB2/viewtopic.php?t=13" target="_blank">http://www.hackzapple.com/phpBB2/viewtopic.php?t=13</a>
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<br />
<span style="font-weight: bold">BOOT TRACE</span>
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- 9600<C600.C6FFM
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- 96FB: 4C 59 FF
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- 9600G
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<br />
Let's examine the code at $0800:
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- the arm is moved to track 1 (routine in $804, in A the phase you want to go to)
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- data is loaded from $B000 to $B7FF
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- $08FB is a JMP $B000
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<br />
Let's break that:
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- 96FB: A9 98 8D FD 08 4C 01 08
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- 9800: 4C 59 FF
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- 9600G
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<br />
Let's examine the code at $B000:
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- clear the screen,
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- set $CC = 0
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- load data at $B100 (1)
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- execute code loaded at $7000
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- set $CC = 1
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- load data at $B100 (2)
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- execute code loaded at $0800
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<br />
(1) The first tables that load data per $800 bytes are located at:
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- phase to move the arm to (equals to track *2): $B0CD
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- address to load data into memory: $B0DB
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- checksum of read data: $B0E9
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=> data is read from track 3 to E from $2000 to $7FFF because $CC = 0
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<br />
(2) The second tables that load data per $800 bytes are located at:
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- phase to move the arm to (equals to track *2): $B0F7
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- address to load data into memory: $B0FA
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- checksum of read data: $B0FD
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=> data is read from track 2 from $0800 to $0FFF because $CC = 1
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<br />
Code at $0800 loads data to the $2000.$BFFF space from phase 1E to phase 44. Then final code execution is passed to $3E00. For those of you who would like to make a ProDOS version of the game, the program is from $2000 to $BFFF.
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<br />
As you may see, the remaining free space is $1000..$1FFF or the $0200.$07FF space, that may be useful for your own routines...
The read routine located at $B100 zeroes its index at $C8 and depending on the value of $CC sets parameters from table 1 or table 2. The routine uses the $C0Ex softswitch and not the $C08x,X softswitches!
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<br />
Entry parameters at $B13D
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A: phase you want to you (one phase = track number * 2)
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phase 2 means track 1, phase E means track 7
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$C9..$CA: address of data to load
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<br />
Other parameters:
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$50: checksum value
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$C2: target phase
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$C7: current phase
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<br />
The routine loads data for 8 pages of $100 bytes (or $800 bytes, or $1000 nibbles), then compares the checksum between data read and $50, then increments the index at $C8.
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<br />
<br />
<span style="font-weight: bold">DISK COPY</span>
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Let's use what Atari offers us: its own routine in $B100 but we need to modify it slightly:
<br />
- read one track
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- copy to the IIgs memory
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- loop until the end of the disk
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<br />
Here is the code:
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<br />
</span><table width="90%" cellspacing="1" cellpadding="3" border="0" align="center"><tr> <td><span class="genmed"><b>Code:</b></span></td> </tr> <tr> <td class="code"> LDA #$18 ; $1800 is our Mount Paramount
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STA $B202
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LDA #$60 ; the RTS opcode
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STA $B205
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<br />
LDA $C0E9 ; turn drive on and wait a little bit
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LDA #$FF
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JSR $FCA8
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<br />
LDA $00 ; we'll begin on track 0
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STA $FF
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STA $C9
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<br />
]LP LDA #$10 ; we'll load data at $1000
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STA $CA
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<br />
LDA $FF ; please read
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JSR $B13D
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<br />
LDA $FF
<br />
JSR $FDDA ; print out current phase
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LDA #$8D
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JSR $FDED ; carriage return (hum)
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<br />
LDY #$10 ; or 8 for those you shrink space
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]LQ LDX #$00 ; let's store read data into our IIgs memory
<span style="font-weight: bold">RE'WRITE' THE 'READ' ROUTINES</span>
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As with Moon Patrol, you are free to use your own read routine, the one from the $C600 space or whatever you like.
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<br />
At first, I use the $C65C read routine ($26..$27 is pointer to the buffer, $3D the sector, $41 the track), that is the one on the DSK image.
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<br />
Then, I had fun including the $C65C code within the $B100..$B2FF space. It also worked, that's quite fun. For those of you interested, I may send info on that one.
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<br />
As that is a tricky stuff to do, please refer to the DSK image and read:
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- T0/S0 is the boot loader of track 1 => The code is loaded at $0800
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- T1/S0..S2 contains the modified read routines (T1/S8..SA for the original ones) => The code is loaded at $B000
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- T2/S0..S2 contains the modified second read routines (T2/S8..SA for the original ones) => The code is loaded at $0800
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<br />
<br />
Your backup copy is now available...
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<br />
Toinet</span><span class="gensmall"></span></td>
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