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diff --git a/docs/research.md b/docs/research.md index 2ef6d64..7eca454 100644 --- a/docs/research.md +++ b/docs/research.md @@ -1,3 +1,59 @@ +# Graphics + +Even though the STM32 is a relatively powerful microcontroller, it will likely +not be fast enough for running game logic, sound logic and a graphics processor +on it's single CPU core. To minimize the risk of overloading the STM32 +processor, all graphics processing and compositing will be outsourced to a +custom PPU implemented on the Basys 3 FPGA. + +Because we're creating a sidescrolling 2D platformer, we don't need a very +complicated graphics processor. We also lack any knowledge about how +'real-world' graphics processors work, so we're basing our design on a product +closest to our target result, the NES. + +## NES graphics + +The NES has a separate coprocessor chip designed to generate video signals +called the RP2C02, which is manufactured by Ricoh. This chip has a lot of +features, some of which we don't need for our game. Here's a quick rundown of +this chip's features and limitations: + +- composite output at 256x224 @ 60Hz (NTSC) or 256x240 @ 50Hz (PAL) +- 256 tiles per tilemap (with 8x8 tiles) +- 2 tilemaps +- 4 palettes per sprite with 64 possible colors +- 512x480 background palette with scrolling +- background scrolling splits +- 64 total sprites on screen (8 per scanline) +- sprites can be drawn before or after the background layer +- PPU control using DMA +- 8K character memory (tilemaps) +- 2K nametable memory +- 256B object attribute memory (OAM) +- tiles can be flipped using OAM +- no frame buffer + +## Custom PPU + +Here's a list of features our PPU should have: +<!-- TODO: expand list with PPU spreadsheet --> + +- 256x240 @ 60Hz VGA output +- single tilemap with room for 2048 tiles of 8x8 pixels +- 8 colors per palette, with 4096 possible colors (12-bit color depth) +- 512x480 background palette with scrolling +- **NO** background scrolling splits +- 128 total sprites on screen (**NO** scanline sprite limit) +- sprites are always drawn on top of the background layer +- PPU control using DMA (dual-port asynchronous RAM) +- tiles can be flipped using OAM +- no frame buffer +- vertical and horizontal sync output + +[nesppuspecs]: https://www.copetti.org/writings/consoles/nes/ +[nesppudocs]: https://www.nesdev.org/wiki/PPU_programmer_reference +[nesppupinout]: https://www.nesdev.org/wiki/PPU_pinout + # Generating audio signals In order to generate sound for this project, a few posibilities exist (see chapters below) |