mirror of
https://github.com/RetroPortingToolKit/psxrecomp
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Matthew Stanley
2aab23968b
docs/disc-speed.md: design doc for per-game disc speed configuration. docs/overlay-discovery.md: design doc for B+A overlay pre-compilation and runtime JIT caching (game-side, future work). tools/dump_tomba_misses.py: one-shot dump of dirty_ram per_pc entries in the game text range, formatted as seed lines. Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>
58 lines
1.9 KiB
Markdown
58 lines
1.9 KiB
Markdown
# Disc Speed Configuration
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**Date:** 2026-05-29
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**Branch:** `overlay-discovery`
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**Priority:** do this first — small, self-contained, no dependencies.
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---
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## Problem
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The runtime emulates PSX CD-ROM timing faithfully (1x = ~150 KB/s, seek delays ~40-500ms).
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Loading screens feel like real PSX hardware. The ISO is on a local SSD; the delay is purely
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artificial. There is no reason a developer or player should have to sit through it.
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---
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## Solution
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Add a `disc_speed` setting to the per-game TOML. The CDROM controller state machine still fires
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in the correct sequence (Idle → Seeking → Reading → INT1) — we just compress the time between
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transitions.
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```toml
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[disc]
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speed = "instant" # "1x" | "2x" | "4x" | "instant"
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```
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- `"1x"` — default, authentic PSX timing. Preserves the original experience.
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- `"2x"`, `"4x"` — scaled multipliers. Useful if a game breaks at instant but tolerates faster.
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- `"instant"` — no timing delays. Data arrives as fast as the host ISO read. Recommended for
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development and testing.
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---
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## Risk
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Games that poll CDROM status registers in a tight loop with an expiry counter, or that use CD
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timing as a crude delay mechanism, may misfire at `"instant"`. Symptoms would be a hang or
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corrupted load immediately after a disc read. The multiplier options exist as a fallback dial.
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Most games — including Tomba — wait on the INT1 interrupt and are indifferent to how quickly it
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fires. `"instant"` is expected to be safe for all titles targeted by this recompiler.
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---
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## Implementation
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Change is localized to `runtime/src/cdrom.c`. The timing delay paths (seek duration, sector
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read interval) check `disc_speed` and either apply the emulated delay or skip it. No other
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subsystem is affected.
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---
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## Relation to overlay-discovery
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Independent. Do this first. Faster disc loads make overlay-discovery iteration faster too —
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each playthrough that warms the overlay log completes quicker.
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