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<td colspan="2"><span class="postbody">What has 48K Bytes and is addictive? Snake Byte! It's the game that works like a charm. A tail of Perilous Purple Plums that's ahead of its time. A game you can sink your teeth into. An antidote for boredom. Snake Byte. Fangs alot, Sirius Software!
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It is the first game I ever played on an Apple II in 1983 <img src="images/smiles/icon_wink.gif" alt="Wink" border="0" />
It is a non-standard disk, only T0/S0 can be copied! Each track contains the equivalent of thirteen sectors with markers DD AD DA followed by thirteen 512 4*4 coded nibbles.
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Last but not least, the first track is track 1.5 <img src="images/smiles/icon_wink.gif" alt="Wink" border="0" />
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<span style="font-weight: bold">BOOT TRACE</span>
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Sirius games are actively protected against boot tracing. That is quite mandatory as, once loaded, there are no more calls to the disk, meaning all the program is loaded into memory!
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- 9600<C600.C6FFM
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- 96FB: AD E8 C0 60
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- 9600G
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Bing! At $0801, the program loads 1024 bytes from $0400 to $07FF, clears memory, EORs our boot page, resets the stack pointer, EORs ZP and then jumps to the next boot stage at $0400
- T3.5 - $2800..$33FF (buffer crosses what has been previously loaded)
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- T4.5 - $3400..$3FFF
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- T5.5 - $4000..$4BFF
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- T6.5 - $4C00..$57FF
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- T7.5 - $5800..$63FF
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- T8.5 - $6400..$6FFF
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- T9.5 - $7000..$7BFF
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- TA.5 - $7C00..$87FF
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<span style="font-weight: bold">DISK COPY</span>
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You now have all the information to get the complete game and create a DOS binary file. As always, I believe it is better to rewrite the read routines <img src="images/smiles/icon_wink.gif" alt="Wink" border="0" />
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The following messages will contain the original boot codes and my own versions.
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What you have to take care of is the stack pointer which is really important in a Sirius software. If you do not set it correctly, the game will hang. Take care also of the false opcodes at $7680, ah! I like such games.
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<span style="font-weight: bold">GETTING THE STACK POINTER VALUES</span>
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At $0867, you have the first EOR routine that sets the stack pointer. The second one at $045F. We cannot modify the original, that would change the stack pointer value. So what?
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Make a copy of the EOR code somewhere else in memory and executes it, just print out the result, let me show you what to do for the first routine:
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- 0367<0867.0871M
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- 0371: 20 DA FD 60
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- 0365: A2 00
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- 365G
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=> result is #$20
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That's all folks. You have all the useful information to make a backup of it <img src="images/smiles/icon_wink.gif" alt="Wink" border="0" />
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<br />
Toinet</span><span class="gensmall"></span></td>
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<td colspan="2"><span class="postbody">My modified first boot process at $0800. Note that the ROM routine could have been reused, it is only for fun <img src="images/smiles/icon_wink.gif" alt="Wink" border="0" />
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