Subject: [stella] RE: Illegal opcodes...another question From: "Dennis Debro" <ddebro@xxxxxxxxxxxxx> Date: Mon, 13 Jan 2003 23:13:45 -0500 |
Sorry for the multiple questions but I want to understand how these illegal opcodes work as I think they may help me... Thomas, I'm looking at the kernel you did for Glenn for Death Race and I have a question. In this code snippet... ; draw car #0: lda #CARHEIGHT-1 ; 2 dcp P0_Y ; 5 bcs .doDraw0 ; 2³ lda #0 ; 2 .byte $2c ;-1 .doDraw0: lda (P0_Ptr),y ; 5 sta GRP0 ; 3 = 18 @20 I see you are using dcp (opcode $c7, decrement and compare). What does this have to do with the y-register? You're not updating y for each scanline, right? Does dcp effect the y-register is some way? I had this question back when you posted skipDraw (http://www.biglist.com/lists/stella/archives/200102/msg00282.html) but I never asked :) Apparently, I'm the only one here that doesn't get it :( Take care, Dennis ---------------------------------------------------------------------------------------------- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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