Allocating variables to specific locations in ram.

[CalinLeafshade]

In the NES, OAM (sprite) data can be DMAed into the PPU by setting the OAMDMA register to the most significant byte ($XX) of an address and then the CPU will DMA into the PPU data from $XX00-$XXFF.

This means that if you have this array in your code then it must be aligned with $XX00 in ram.

Is it possible to preallocate this memory somehow at a particular location and then reference it in C? I assume it would be done in the linker with a section but I don't know how to do that.

[CalinLeafshade]

This is my current solution which seems to work ok but I'm not sure if it's somehow inefficient.

static u8 sprites[256] __attribute__ ((aligned (256)));

(Why do I always raise an issue just before I find a solution?)

[mysterymath]

Yep, that's the idiomatic pattern for this.

You can also decrease the memory usage incurred by alignment by passing --sort-section=alignment. This will order input sections within each output section by decreasing alignment, which helps decrease the amount of filler emitted in the final object file. It's not a complete binary packing solution though; I'd eventually like to have one, but that sort of thing isn't really in GNU ld or lld, so it'd be greenfield work.

I'll leave this open to track the work of making --sort-section=alignment the default.

[mysterymath]

Done.