N64 Cartridge Bus Emulator

This is an attempt to emulate the N64 cartridge bus using a fast modern SBC. This project currently uses the "Allwinner Nezha" development board but will switch to the "Sispeed Lichee RV" in the future (assuming everything works) as the Sispeed board is much cheaper ($30 vs $100) and it exposes enough IO on the board without needing soldering.

How it works

This project works by booting a baremetal program on the board that using interrupts to respond to the ALE_L, ALE_H, and /READ signals from the N64 bus, it then loads the appropriate data directly from RAM on the SBC and makes it available on the address bus.

How to use it

The makefile assumes that you have a toolchain called riscv64-unknown-elf in your path (I.E. riscv64-unknown-elf-gcc and friends exist in your path). Assuming you do you should be able to just run make to have it generate a binary file called n64_cart.bin that represents the program. This program assumes that it will be loaded into memory on the board at address 0x45000000. To load the program on hardware I am currently using uboot with the loadx command to load the binary over serial. Using the screen program as your serial terminal you can do the following to load the program in uboot

1. run screen pointed to the right ttyUSB device
2. once uboot starts up, press any button to get a terminal in uboot
3. run loadx 45000000 in uboot
4. in screen preform the key combination of CTRL-A + : and then type in exec !! sx out.bin. This will output the binary file in the XMODEM format for uboot to load.
5. Once the program is done loading run go 45000000 to run the application

TODO

Currently this only implements the framework to get this idea working. There is still a lot of work to do to test if the Allwinner D1 chip is fast enough to emulate the N64 cartridge bus.