design.md

NES260 design

Board design,

• NES_KV260.v is the main module. The whole NES machine (CPU, PPU, APU, memory controller, memory mapper) is in there.
• nes_dp.v converts NES video signal to 1080p and feeds into PS's live video input, which in turn drives HDMI output.
• Everything runs at 21.47Mhz (NES main clock) except part of nes_dp, which runs at 148.5Mhz (1080p pixel clock). Video is scaled from 256x240 to 1024x960 (4x).
• A .nes ROM is first sent to the ARM CPU (PS) through UART_1. PS program there (sw/*) then forward it to PL through NES_KV260's AXI4-Lite port (s00_axi).
• Game controllers are handled in a similar way. Button presses are detected on the PC, sent to PS and finally reaches PL through AXI.

Cartridge of up to 2MB are supported, which should cover 95% or more games. Cartridge ROM, internal RAM (2KB) and VRAM (2KB) are all stored in the on-chip UltraRAM (total 2304KB, used 100%). PS DDR memory is not used by FPGA. Here's a rough memory layout,

UltraRAM layout:
256K words, every word is 9 bytes (72 bits)
        71:64             63:0
   0 +------------+------------------+
     |  PRG RAM   |      PRG ROM     |
128K +------------+------------------+
     |Internal RAM|      CHR ROM     |
     |    VRAM    |                  |
256K +------------+------------------+

Final resource usage,

Obviously UltraRAM is the heavily-used resource here.

Build instructions

Use Vitis/Vivado 2021.2 with Y2K22 patch.

Vivado build,

1. Create a new project with K26 SoM. Don't forget to choose the KV260 Starter Kit board in "connections"
2. Import all source files in fpga/hdl.
3. Import constraints file fpga/pmod.xdc.
4. Create board design with fpga/design_1.tcl. (Tools->Run Tcl Script)
5. Generate Bitstream. Wait 10 minutes.
6. File->Export->Hardware->Include bitstream to get nes260.xsa.

Vitis app and boot.bin,

1. Create a platform with nes260.xsa
2. Create an application project nes, import everything in sw/ as source code.
3. Build and get nes_system/Debug/sd_card/BOOT.bin.

Credits

• fpganes was originally authored by Ludvig Strigeus.
• Greg Taylor's IMX219 MIPI sensor 1080p/30fps video to Ultra96-V2/Kria KV260 FPGA DisplayPort code helped a lot in getting live video through PS to work.