Oziphantom wrote:Set the Data Bank Register to $7F ( or 7E if you want)
DP relative hits your 256 bytes of "registers" in 00:XXXX
I would not recommend this, because even though the DP access only takes 3 cycles, they're slow cycles because you're hitting RAM. One of the keys to performance on the SNES is to minimize excessive RAM reads/writes.
Oziphantom wrote:if you need to read from another bank or ROM
24bit ABS will read from wherever, give you have 16 bit index registers you can do
LDX #address in bank
LDA $820000,x ; reads the byte you want
This is alright for one-off reads, but if you're accessing lots of values out of a different bank, better to set the data bank register and use absolutes.
Oziphantom wrote:or use a 24bit pointer in the DP and do direct indirect indexed long or direct indirect long modes to pull data from ROM/other RAM.
This is an interesting idea, but would probably need some values pre-stored during scene initialization, or else it'd be slower than absolute long.
You don't really need 256 fake registers. My take is set program and data bank to 80, and set data bank inside of, or before calling into, routines where you want to use data from elsewhere (but only when you need to).
You're not going to want to use a data bank like 7e or 7f as a general purpose thing if it's going to prevent you from accessing ROM via absolute addressing, which means harder access to read-only data structures and lookup tables that you can access with fast cycles (assuming you're using FastROM).
So yeah, I'd basically just take a "set it when you need it" approach to SNES programming. The whole bank thing definitely creates some mental barriers, but once you become more familiar with the addressing modes, and you know how to work the data bank register, it'll become a lot more tangible.