DVD check Pattern

@PS_2

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Playstation 2 tutorials

 · 13 Aug 2018

DVD CHECK (cdMode pattern)

As we have discoverd how to find the DVD CHECK with the sceCdMmode for the first wave of game... now we can detect the DVD CHECK in this way....
Here it is the code of a cdMode routine that check the type of media (i think)....
(IDA list)

 
CdMode :  
.text:0034B7D8 sub_34B7D8:  
.text:0034B7D8  
.text:0034B7D8  
.text:0034B7D8 var_50 = -0x50  
.text:0034B7D8 var_40 = -0x40  
.text:0034B7D8 var_30 = -0x30  
.text:0034B7D8 var_20 = -0x20  
.text:0034B7D8 var_10 = -0x10  
.text:0034B7D8  
.text:0034B7D8 addiu $sp, -0x50  
.text:0034B7DC sd $s1, 0x50+var_30($sp)  
.text:0034B7E0 sd $s0, 0x50+var_40($sp)  
.text:0034B7E4 lui $s1, 0x37  
.text:0034B7E8 sd $s2, 0x50+var_20($sp)  
.text:0034B7EC daddu $s0, $a0, $0 
.text:0034B7F0 sd $ra, 0x50+var_10($sp)  
.text:0034B7F4 addiu $s2, $s1, 0x5940  
.text:0034B7F8 jal scmd_prechk  
.text:0034B7FC li $a0, 0x22  
.text:0034B800 bnezl $v0, loc_34B810  
.text:0034B804 sw $s0, dword_375940  
.text:0034B808 b loc_34B884  
.text:0034B80C daddu $v0, $0, $0  

This routine isnt in the FLIRTS of PS2 so you can find it with a simple TEXT SEARCH of scmd_prechk
You can find many scmd_prechk, but if you compare the routine with you results, you can be sure that this is the routine you are searching for....
In some cases you can modify this to change all the CALL of this routine.... but i prefer made the change after this call....
So now you must search the name of SUB (in this case sub_34B7D8 for SMUGGLERS RUN 2 if i remember well....).
You will find the CALL of SUB and after that the normal

 
li      $a0, 2 

So make the normal change.....

 
li	$a0, 1 

Sometimes you can try changing this from the above routine:

 
daddu $s0, $a0, $0              (in hex editor 2D 80 80 00) 

with

 
li $s0,1 			(in hex editor 01 00 10 24)