116 lines
6.4 KiB
NASM
Executable File
116 lines
6.4 KiB
NASM
Executable File
*
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* ROBOTRON 3-10-82 RELEASE 1
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*
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ORG $26B7
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FCB $65
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ORG $5E77
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FCB $68
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ORG $DE54
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FCB $1B,$1B,$1B,$1B,$1B,$1B,$1B,$1B
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*
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* CHECKSUMS
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*
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*
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* 0-$4D
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* 1-$19
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* 2-$D9
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* 3-$1B
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* 4-$7E
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* 5-$DD
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* 6-$F1
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* 7-$3E
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* 8-$6D
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*
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* D-$4D
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* E-$48
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* SUPER CHECKERS - 98F3 = $37
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* BE72 = $4A
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**************************************************************************
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* *
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* Here is a detailed explaination of the Robotron 2084 *
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* "JAP ZAPPERS". This was a primitive system setup to *
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* try and make it more difficult for game copiers to *
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* Modify the game. There were scrambled sections of the *
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* code that would try and monitor "random" checksums *
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* of regions of the code. If they detected that the code *
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* had been modified, they would cause random program *
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* events to occur at a low frequency (the random and *
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* low frequency combination would make it harder to track *
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* down the culprits). We always assumed that developers *
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* with good tools would find these quickly, but Christian *
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* Gingras, removed this small nuisance while trying to *
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* fix the other bugs he had found in the program (with *
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* the aid of his Radio Shack Color Computer). *
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* *
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* There are 2 regions for which checksums are kept. The *
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* checksums are not the sum of all bytes, but the sum *
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* of every 8 and 16 bytes respectively. The first checksum *
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* is the sum of every 16th byte from $0007 to $8927 inclusive *
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* and is stored at $98F3 (HCK1). This sum should come out to *
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* $37. The second checksum is the sum of every 8th byte *
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* from $D015 to $EAAD and is stored at $BE72 (HCK2). This sum *
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* should come out to $4A. *
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* *
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* There are 6 places in the software that are concerned *
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* with the checksums. *
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* *
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* In RRTEXT, at label WORDZ (the call for message handling) *
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* there is a check of HCK1 for its $37 value, and handling *
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* to zap if incorrect. *
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* *
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* In RRS22, the code to set the HCK1 value (by performing the *
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* required addition) is found within the PINIT routine. *
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* PINIT is used to initialize the process structure at the *
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* start of each turn. *
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* *
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* In RRS22 there is a check of HCK1 for its $37 value in the *
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* ASCAN routine. ASCAN is called at the start of each wave *
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* by each object to make sure the space it wants is un-occupied *
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* *
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* In RRG23 the code to setup the HCK2 value (by performing *
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* the required addition) is found within the game start *
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* routine (START1 and START2). *
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* *
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* In RRX7 there is a check of HCK2 for its $4A value in *
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* the explosion starter (EXSTV). *
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* *
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* In RRB10 there is a routine that computes the HCK2 value *
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* (on the fly in case the copiers goose the values into *
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* ram) and zaps if it does not come up with the $4A value. *
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* This is found in the brain starter (BRNSTV) and is run *
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* in any waves that contain BRAIN robots. *
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* *
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* The checksums are computed with the equivilents of the *
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* following code: *
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* *
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* HCK1 ($98F3) = $37 *
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* *
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* clra *
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* ldx #$0007 *
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* loop: adda 0,x *
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* leax $10,x *
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* cmpx #$8935 *
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* blo loop *
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* sta hck1 *
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* *
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* *
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* HCK2 ($BE72) = $4A *
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* *
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* clra *
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* ldx #$d015 *
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* loop: adda 0,x *
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* leax $8,x *
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* cmpx #$EAB1 *
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* blo loop *
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* sta hck2 *
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* *
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* *
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**************************************************************************
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END
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