Matthew Stanley
1.9 KiB
Disc Speed Configuration
Date: 2026-05-29
Branch: overlay-discovery
Priority: do this first — small, self-contained, no dependencies.
Problem
The runtime emulates PSX CD-ROM timing faithfully (1x = ~150 KB/s, seek delays ~40-500ms). Loading screens feel like real PSX hardware. The ISO is on a local SSD; the delay is purely artificial. There is no reason a developer or player should have to sit through it.
Solution
Add a disc_speed setting to the per-game TOML. The CDROM controller state machine still fires
in the correct sequence (Idle → Seeking → Reading → INT1) — we just compress the time between
transitions.
[disc]
speed = "instant" # "1x" | "2x" | "4x" | "instant"
"1x"— default, authentic PSX timing. Preserves the original experience."2x","4x"— scaled multipliers. Useful if a game breaks at instant but tolerates faster."instant"— no timing delays. Data arrives as fast as the host ISO read. Recommended for development and testing.
Risk
Games that poll CDROM status registers in a tight loop with an expiry counter, or that use CD
timing as a crude delay mechanism, may misfire at "instant". Symptoms would be a hang or
corrupted load immediately after a disc read. The multiplier options exist as a fallback dial.
Most games — including Tomba — wait on the INT1 interrupt and are indifferent to how quickly it
fires. "instant" is expected to be safe for all titles targeted by this recompiler.
Implementation
Change is localized to runtime/src/cdrom.c. The timing delay paths (seek duration, sector
read interval) check disc_speed and either apply the emulated delay or skip it. No other
subsystem is affected.
Relation to overlay-discovery
Independent. Do this first. Faster disc loads make overlay-discovery iteration faster too — each playthrough that warms the overlay log completes quicker.