In 0.2.2c

poke4(dst,peek4(src,len))

takes 0% CPU. e.g.

poke4(0x6000,peek4(0x0000,2048))

to copy spritesheet to screen for free.

Can we rely on this behavior? (please)

Sorry to be a wet blanket, but I really hope we're not meant to be able to rely on this. It'd let people write carts that could do far too much to run on devices like a Pi. That seems like way too much Lua stack hackery (stackery?) going on for it to be free.