Popslide is a video memory update buffer framework for the Nintendo Entertainment System.
NES games need to update video memory in numerous ways during gameplay. But the frame rendering circuitry in the PPU has exclusive access to video memory while it sends the picture to the TV. So games usually buffer updates in RAM. An unused part of the stack is a convenient place to stash such a buffer, big enough to hold the largest practical VRAM update on NTSC.
Some games have only one update routine because all the updates they do are so similar. Others have multiple update routines, one for each kind of update, such as nametable columns, nametable rows, rectangular areas, tile uploads, attribute uploads, and the like. Still others embed information about the shape of an update in the buffer. This is the approach used by Super Mario Bros.
and other games using NES Stripe Image format
Popslide interprets an NES Stripe Image buffer in the stack page, using PLA
as an autoincrementing read instruction. It comes in three forms: a looping version, a partially unrolled (16x) version, and a fully unrolled (64x) version.