Its my first post here, I have this small issue with my code. The Mesen debugger shows ISC* $FFFF on every single address in ROM from $8134 - $BFFF and $C10D - $FFFF. (So basically in the free space of the cpu address space)
Not sure what causes it though, nesasm3.1 may be inserting this by mistake.
https://github.com/baboomerang/6502NES- ... rogram.asm
Here is my entire file so you guys can check it out.
Maybe there is something wrong in my understanding of the 6502 so any insight would be greatly appreciated.
attached below are pictures of the debugger
Programmable memories are "empty" when they hold $FF, and require modification to hold any other value. By putting $FF in these blocks, it speeds up the process of programming, because it can entirely skip over those bytes.
My bad for the newbie question, these 6502 quirks are fascinating.
Also, what about this section? Does mesen ever confuse graphics data for code? (Can it even?)
I found these (and a few more) scattered inside the bottom half of the rom.
Code: Select all
ISC* $FFFF,X ISC* $2536,X NOP* $FF,X AND $36,X RLA* $FF,X AND $3B3A,Y ISC* $2321,X ORA ($0F,X) BIT $36 PHP SLO* $3802 ROL $0F AND #$15 NOP* $0F,X STP* SEC ROL $7A STP* BRK