Weird code in SBZ transporter tubes

If you have 50 rings at a certain transporter in the level, it takes you to an alternate path with a bunch of goodies. It's pretty nifty! :P

 

Woah. This is very interesting.

 

Doesn't this mean that the "locret_1675C:" doesn't do anything? (From later in assembly

Code (Text):

1. locret_1675C:
2.         rts

 

Nope, it exits the subroutine. All locrets do that =P

And bcs is branch if carry set - it branches if the carry flag is set after an operation.

 

never knew that, ill have to check it out next time im on that game...

 

Yea, pretty much just a shortcut for the level.. :P

 

I learned about this a while ago, it's quite a nice little feature. Now that I know where it's located, I can edit it :P thanks

 

blt is signed, and checks different CCR bits
bcs is unsigned.

 

So how exactly does the code work? I'm new to asm and I'm trying to figure out how a lot of the stuff works. - If the "locret_1675C" is branched to, but it immediately rts's and exits - how does the game know to do anything special?

 

That code checks to see if the necessary conditions are NOT met - if they ARE met then the code immediately after that code is run and the transporter goes to the part with the hidden goodies.

 

That is correct. By the way, I suggest you google for "m68000 reference manual" and grab a pdf of the motorola m68000 programmer's reference manual. It should assist you with similar ASM questions in the future.

 

Actually RTS will pull the the PC from the stack, but in most cases what you said is true (unless someone fiddles with the stack, heh).

Ie. sometimes you can see lea 4(sp),sp, or something similar. Basically this makes RTS come back to PC 2 jsr/bsr's away. Heh =P

 

There's also addq.b #4,sp which disables the next subroutine call. =P

 

lea 4(aX),aX does the same as addq.l #4,aX

also, using addq.b for SP is sick!

 

No need to apologize. I was just suggesting that that'll give a faster response than S2beta does most times.