uNES is a basic NES emulator, currently still under development. In its current state it supports full, cycle-accurate CPU emulation.

uNES is written completely in C, and is meant to be fast and performant. The emulator avoids dynamic memory allocation entirely, and is able to run 80,000,000 instructions per second, clocking in at just under 300 MHz.

• Hardware quirks are, for the most part, unimplemented.
  • The quirk w.r.t indirect jumps (documented here) has been implemented.
• The emulator is not 100% cycle-accurate---i.e. it will execute all of an instruction's logic at once, rather than cycle by cycle.
• Undocumented/illegal opcodes are, for the most part, unimplemented.
  • Opcode 04 is implemented, but it is a 2-byte NOP. Not very interesting.

Each NES CPU instruction has been stress-tested against 10000 randomly generated test cases and "verified" to work properly (althrough there is always a small chance of a buggy instruction getting extremely lucky and passing all 10000 test cases).

In the future, common mappers will be implemented so that execution of arbitrary .nes files is trivial. Currently, cpu_driver.c is specifically configured to run blargg's offical.nes test ROM. To test the execution of this ROM, first download offical.nes and copy it to eval/execs. Then run

make speedtest

(this will issue some warnings, but they are safe to ignore). Finally,

bin/speedtest

will execute offical.nes for 10 seconds and print some useful performance and debug information to stdout:

PC: e000 A: 0 X: 0 Y: 0 SP: fd status: 24 remaining cycles: 0 deferred: 0
815052076 instructions executed in 2852708669 clock cycles
PC: 8353 A: 2d X: 0 Y: 0 SP: f4 status: 27 remaining cycles: 1 deferred: 1