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https://github.com/RetroPortingToolKit/psxrecomp
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Matthew Stanley
958a928d14
New runtime/src/psx_icache.c: direct-mapped (4 KB / 256-line) instruction-
cache fetch cost, transcribed from Beetle PS_CPU::ReadInstruction:
HIT (TV == addr) -> +0, no give-back clear
MISS, KSEG1/uncached -> +4 (BIOS ROM)
MISS, cached (KSEG0/KUSEG) -> +3, then +1 per word refilled from the
missing word to the line end (earlier words
stay invalid); also clears the load give-back.
Mirrors only the per-word TV tag array (cost + tag state; the value is already
in hand). Wired into the dirty-RAM interpreter (exec_one) per instruction,
charged BEFORE the §1 base — Beetle order.
New ruler #2 loop `icache_miss`: loop top + a victim 0x1000 apart alias the
same direct-mapped line with different tags, forcing a refill miss every
iteration (other loops are all-hits after warm-up).
VALIDATED interp vs Beetle (PSX_FORCE_INTERP=1 PSX_ICACHE=1): icache_miss
native +14 == Beetle +14 (per-iter 17); the other 12 loops unchanged at +0
fetch. So the I-cache hit AND refill-miss costs are MEASURED equal to the
oracle on the interp path.
Opt-in via PSX_ICACHE=1 (default OFF) — charging fetch cost in only one
backend would fork mixed compiled/interp timing. Production activation +
the compiled-path emit (per cache-line leader) + ruler #1 cold-spike
validation are Stage 2. Default-off => no production change (the interp's
fetch call is a no-op without the env).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>