emulation - 6502 and little-endian conversion -

for fun i'm implementing nes emulator. i'm reading through documentation 6502 cpu , i'm little confused.

i've seen documentation stating because 6502 little-endian when using absolute addressing mode need swap bytes. i'm writing on x86 machine little-endian, don't understand why couldn't cast uint16_t*, dereference that, , let compiler work out details.

i've written simple tests in google test , seem agree me.

// implementation of read16 #define read16(addr) (*(uint16_t*)addr)  test(memmacro, read16) {   uint8_t arr[] = {0xff,0xcc};   uint8_t *mem = (&arr[0]);    expect_eq(0xccff, read16(mem)); } 

this passes, appears supposition correct, thought i'd ask more experience i.

is correct pulling out operand in 6502 absolute addressing mode? possibly missing something?

it work simple cases on little-endian systems, tying implementation feels unnecessary when corresponding portable implementation simple. sticking macro, instead:

#define read16(addr) (addr[0] + (addr[1] << 8)) 

(just pedantic, should make sure addr[1] can't out-of-bounds, , need add more parentheses if addr complex expression.)

however, keep developing emulator, find it's natural use pair of general-purpose read_mem() , write_mem() functions operate on single bytes. remember address space split multiple regions (ram, rom, , memory-mapped registers ppu , apu), having e.g. single array index won't work well. fact memory regions can remapped mappers complicates things. (you won't have worry simple games though -- recommend starting donkey kong.)

what need figure out region or memory-mapped register address belongs inside read_mem() , write_mem() functions (this called address decoding), , right thing address.

returning original question, fact you'll end using read_mem() read individual bytes of address anyway means uint16_t casting trickery less useful. simplest , robust approach w.r.t. handling corner cases, , every emulator i've seen in practice (nestopia, nintendulator, , fceux).

in case you've missed it, #nesdev channel on efnet active , resource way. assume you're familiar nesdev wiki. :)

i've been working on emulator can found here.