Extends the two-process parity ring so each row carries, per watch word, the
exact store PC + guest cycle + frame + (approx) writing TCB of the most recent
write to that word. parity_trace_note_write() maintains the table from BOTH
processes' write paths (native: memory.c psx_write_* with g_debug_last_store_pc;
Beetle: beetle_libretro.cpp wtrace_callback with the store pc). Both parity_dump
serializers emit the new wwpc/wwcy/wwf/wwt arrays (identical wire format), and
parity_diff.py prints a side-by-side WATCH PROVENANCE block at the divergence.
This turns "the gate-input value diverged" into "who/when produced it" -- the
instrument ChatGPT recommended for the MMX6 over-fast wedge.
First result (MMX6 cutscene->gameplay, watch 0x80071088/0x800CD3F8/0x8006D9AC/
0x800CD3FC/0x800CD404/0x800200F4): the cutscene-setup func_8001CB3C (writer pc
0x8001CB7C of countdown 0x800CD3FC) runs ~99.7M guest cycles / ~176 frames
EARLIER on native (cyc 998,597,937 frame 1769) than Beetle (cyc 1,098,296,890
frame 1942) -- same writer PC, fired early. On Beetle the state struct
0x800CD3F8 is never touched by game code (stays BIOS-init 0 -> setter path); on
native it advances. The over-fast wait is localized one level above the state
machine, at whatever schedules func_8001CB3C.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
End the "somewhere upstream" blindness with a reusable first-divergence
instrument (PRINCIPLES.md "find the first divergence; is the value WRONG or the
behavior MISSING"). A TCB-scoped, freeze-on-trigger control-flow ring with an
identical struct + JSON wire format on both processes, so a generic sequence-diff
(tools/parity_diff.py) locates the first logical divergence between recomp and
oracle — not a frame diff.
- parity_trace.{h,c}: armed-from-boot ring, gated on current_tcb==watched_tcb,
latches on a configured trigger target so the pre-divergence window survives
the wedge loop. Up to 6 watch-word snapshots/row. Self-contained TU shared by
both binaries; frame source decoupled via parity_host_frame().
- fntrace.c: per-dispatch producer hook (cheap armed gate on the hot path).
- traps.c: YIELD control-event hook in the scheduler switch.
- main.cpp: env-armed from boot (PSX_PARITY_TRACE=1; TCB/trigger/watch tunable),
defaults target the MMX6 cutscene wedge.
- debug_server.c: parity_dump + parity_ctl commands.
- tools/parity_diff.py: pulls both rings, sequence-diffs by (kind,pc,target).
First use (MMX6 freeze) confirmed MISSING behavior, not a wrong value: native
thread1 is permanently parked at func_8002000C resume (TCB EPC 0x800200F4),
handshake flag 0x8006D9AC never set (0 across 16384 rows), setter func_8001344C
never runs; thread1 re-resumes a dead func_8002000C frame whose saved-ra slot was
reused -> jr 0x800CD3F8 wedge. Upstream context-staleness/scheduling root.
Beetle mirror producer + the cross-process diff are the next step.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Matthew Stanley