Settings & performance

The defaults are tuned. If a game boots and plays at full speed, change nothing. If it is slow, follow the steps below in order, and read the warning about overclocking first.

The defaults

Accurate blitter, stock clocks, experimental timing models off, HLE CD boot, and RISC Idle-Loop Fast-Forward on, which is the biggest speed-up the core has. Per-title defaults are also on: about a dozen recognised games (and the JagDoomEX hacks) get 2x internal resolution or true colour, and the Enhancement Profile decides whether that is allowed on your hardware.

Five settings matter: Enhancement Profile, Internal Resolution, Blitter, Frameskip, and for CD games CD Boot Mode. The rest are diagnostics, controllers and networking.

When a game runs slow

In order. Stop as soon as it is fast enough.

  1. Enhancement Profile to Performance. It stops the per-title database from switching on 2x resolution and true colour. On Alien vs Predator those two measured about 30% of the frame. Auto, the default, already turns them off on 32-bit ARM and drops them early if the audio buffer cannot keep up. Options you set yourself always win.
  2. Internal Resolution 1x, True Color off. The manual version of step 1, for any game.
  3. Frameskip to Auto. Skips presenting frames when the frontend reports an audio under-run. Presentation only: the emulated machine still runs every frame, so savestates, run-ahead and netplay are unaffected. It needs a frontend that reports audio buffer status.
  4. Blitter to Fast. Measured 1.21x typical, up to 1.58x on the title that gains most. It can still break some games with wireframe artifacts or missing geometry, so switch back the moment anything looks wrong.
  5. Only then consider overclocking, after the next section, because it can make things worse.

There is no internal speed limiter. Pacing is your frontend’s job.

What cancels idle-skip read before overclocking

RISC Idle-Loop Fast-Forward skips the redundant iterations of the wait loops the GPU and DSP spend most of each frame in, and it is exact: savestates, run-ahead and netplay are unaffected. It switches itself off entirely when any of these is set:

SettingValue that disables idle-skip
RISC (GPU/DSP) Clock Scaleanything other than 1x
DRAM Timingenabled
GPU Pipeline Timingenabled
Blit Memoizationenabled or verify

M68K Clock Scale at any value, and Blitter Bus Timing, do not affect it.

Overclocking the RISC to speed up a slow game can make it slower. RISC Clock Scale 2x doubles GPU and DSP cycles and also forfeits a 66-87% cut in DSP work. On a DSP-bound title you trade the bigger win for the smaller one.

The core warns you. Enable idle-skip alongside any setting above and one [perf] line in your frontend log names the culprit. It only warns. Your settings are never overridden.

Jaguar CD

CD Boot Mode defaults to HLE: fastest, broadly compatible, no BIOS files. Try real BIOS if a disc misbehaves. The two are different implementations of the same boot, and a few titles work under one and not the other. CD Read Speed (HLE only) defaults to 2x; 1x is hardware-faithful and instant is fastest.

Full guide

The repository carries the complete guide: every option, which ones need a restart, a symptom-to-setting table, and the measurements behind the figures above. settings-and-performance-guide.md.