Sylpheed/docs/re/structures/isl-schedule.md

✅ Each phase carries a TIMELINE — 675 scheduled routines across the disc

The trailing data table found at the end of every phase region (isl-stream-entry-points) is decoded. It is the mission's scripted event schedule.

Layout

After the phase's code ends — at the first value of that phase's mission-level 0x1883 record — comes a run of 8-byte typed records, tag 0x19 = int, 0x1A = IEEE float:

int   N                                     -- entry count
N x [ int offset ; float t ; int kind ]

1 + 3N matches the record count in every phase measured: Stage 02's three phases hold 76, 40 and 55 records for N = 25, 13 and 18.

✅ The checks

schedule entries disc-wide	675
0x1A float records disc-wide	675 — the same number, independently counted
offsets landing on the instruction stream	675 / 675 = 100.0 %
control: random 4-aligned offsets	33.3 %

The float count and the entry count are derived by different routes and agree exactly, and every single offset resolves. kind is 0 (556) or 5 (119).

✅ The floats are seconds

The distribution is unmistakable: 0, 0.5, 1, 4, 5, 30, 50, 60, 90, 120, 150, 170, 180, 210, 240, 270, 300, 330, 360, 420, 570, 1020, 1080, 1140, 1170 … mission times, not fractions.

And the targets are what a schedule would point at — small one-shot coroutines:

002C04:  set.i  local[0] = 1
002C1C:  set.i  local[4] = 1
002C34:  set.f  local[8] = 0.4
002C50:  call   builtin106(0x1, 0x1, 0.4)
002C5C:  call   end_coroutine

🟡 A runtime cross-check — consistent, and not proof

The closed REMAINING OB work measured, on the emulator over n=5 runs, that Stage 02's squadrons arrive at t = 0, 120 and 210 s. All three times are in phase 1's static schedule, and 120 and 210 each appear twice, which is what two squadrons arriving together would look like.

⚠️ Stated as consistency rather than confirmation: these are round numbers, and phase 1 has ~22 distinct times spread over 0–1170, so three specified round values all being present is not by itself unlikely. The doubling is the sharper detail, and it was not predicted in advance.

Artefacts

data/isl-stage02-schedule.txt and data/isl-schedule-all.txt (all 28 stages, 675 entries), generator isl_report.py schedule. The four earlier artefacts regenerate byte-identical.

✅ The CONSUMER — sub_822748D0, called from ScriptPhase::Update

Found statically. The phase initialiser sub_82270DF8 takes the 0x1883 record's six words as arguments and stores

82270FC8  stw  r26, 232(r30)     ; [phase+232] = code base        (already documented)
82270FDC  add  r10, r26, r21     ; base + entry_a
82270FEC  stw  r10, 240(r30)     ; [phase+240] = THE TABLE POINTER

[phase+240] has exactly two readers in the ISL region, and one of them, sub_822748D0, is called from sub_82263408 = ScriptPhase::Update. It is the timeline walker, and it confirms every field of the decode independently:

822748E0  lwz  r11, 240(r30)      ; the table
822748E4  lwz  r10,   4(r11)      ; N -- the count, at table+4          ✓
822748E8  addi r11, r11, 8        ; skip the count record               ✓
822748F4  addi r31, r11, 20       ; -> group+20
822748FC  lwz  r11,   0(r31)      ; kind   at group+20                  ✓
82274900  lfs  f0,   -8(r31)      ; t      at group+12, as a FLOAT      ✓
82274904  lwz  r10, 104(r30)      ; clock array A
82274908  rlwinm r11, r11, 2,0,29 ; kind * 4
8227490C  lfsx f13, r10, r11      ; A[kind]
82274910  fcmpu cr6, f13, f0
82274914  bc   ... skip
82274918  lwz  r10,  88(r30)      ; clock array B
8227491C  lfsx f13, r10, r11      ; B[kind]
82274920  fcmpu cr6, f0, f13
82274924  bc   ... skip
8227492C  lwz  r5, -16(r31)       ; offset at group+4                   ✓
82274930  lwz  r4, 232(r30)       ; the code base
82274934  bl   0x822737C8         ; start the routine
8227493C  addi r31, r31, 24       ; STRIDE 24 = three 8-byte records    ✓

Count position, float position, offset position and the 24-byte stride are all confirmed by the engine's own reader rather than by my structural inference.

✅ kind is a CLOCK INDEX, not a flag

rlwinm r11, r11, 2, 0, 29 then lfsx — kind is multiplied by 4 and used to index float arrays at [phase+104] and [phase+88]. So kind selects which timer the entry is scheduled against, and 0 / 5 are two of at least six.

The entry fires only when its t lies between the two clock readings — the classic "which events did this frame cross" test, with one array holding the previous value and the other the current. 🟡 Which array is which follows from the comparison directions (A[kind] > t skips; t >= B[kind] skips) and is stated as a reading of those two branches, not measured at runtime.

✅ And the clock is PER PHASE

Both arrays are fields of the phase object, so each phase has its own timers — which is why every phase's table restarts at t = 0. That was previously an inference from the layout; it is now a read.

🟡 Not settled

• This is not what starts the unreachable code. All 675 targets are already reachable — 0 are unreached run-starts — so the ~15 % gap stands.
• What the six clocks are. kind indexes arrays at [phase+88] and [phase+104]; only indices 0 and 5 are ever used by the data, and neither array's contents were traced to a source.
• sub_822737C8, which actually starts the routine, is not read — it is presumably the same spawner start_coroutine uses, but that is unchecked.