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Drop SASI on capacity, then find the budget never had the disk in it

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USER DECISION: drop the `sasi` profile. Not on bandwidth -- on capacity. A SASI
volume is 40 MB, and the 22.8 min of unique scene footage on the source Blu-ray
(streams 00000-00201, measured, not recalled) is 146 MiB at the LOWEST rate this
codec makes -- more than the machine's whole 4-unit SASI space. `scsi` is the
only profile now. FINDINGS 32.

Then the user asked whether we were drawing the wrong conclusions about PIO vs
DMA, and we were, more broadly than the question implied. Every CPU figure in
FINDINGS 24-34 is scored against the full 833,333 cycles/frame with nothing
subtracted for moving the bitstream off disk. Debiting the HD63450 cycle-steal
at the long-standing 8 clk/word ESTIMATE, "1 frame of 120 misses" becomes 84 of
120, median 112.4%. PIO at the span rate is 99.8% of the machine. Spans buy
cycles by spending bandwidth and the bandwidth returns as steal, so 31.6's "fits
completely" becomes a worst frame of 114.3%. 10 fps absorbs it: median 93.7%,
1/120. FINDINGS 35. `11_cpu_budget.py` takes --io dma|pio|none, defaults to dma,
and warns if asked for none.

Also landed:
- item 1 done: the cost model checked against the 68000 on a cost-aware
  container, -3.07% to +0.01%, whole-window mean -1.22%. FINDINGS 34.
- item 4 done: the container carries its own 4-byte record alignment (DLX2).
  94/120 record starts were on odd addresses -- an address error, not a slow
  read -- now 0/120 for 16 B/s. Re-encoding reproduces 31.1 exactly. FINDINGS 33.
- a `scsi` window does not fit the 2 MB machine the rig emulates (2.84 MB of
  stream past a 0x200000 ceiling). The gate now verifies 80 of 120 frames and
  SAYS so, and fails loudly when the pass does not complete, instead of
  reporting a phantom 49,005-pixel diff. FINDINGS 36.

Three near-misses this session had one shape: an unobservable run nearly
produced a false finding. stdbuf -oL on any MAME job that prints progress -- a
file is block-buffered too, and a run that is merely finishing looks exactly
like one that is wedged.

check.sh ALL GREEN.

Claude-Session: https://claude.ai/code/session_01194oWYW8DQXK1SZ2DnChW6
This commit is contained in:
prosolis
2026-08-23 17:09:47 -07:00
parent 06b98d4b47
commit 7d365b3ff5
12 changed files with 664 additions and 129 deletions
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tools/encoder/encode.py
+24 -7
View File
@@ -1,7 +1,7 @@
#!/usr/bin/env python3
"""Encode one scene to the DLX bitstream, at a chosen quality profile.
python3 tools/encoder/encode.py <frames_dir> <out.dlx> [--profile sasi|scsi]
python3 tools/encoder/encode.py <frames_dir> <out.dlx> [--profile scsi]
[--lam N] [--fps 12] [--preview out.png]
[--fixed-lam] [--rc-floor profile|open]
@@ -16,7 +16,7 @@ Container (little-endian is WRONG here -- the 68000 is big-endian, so every
multi-byte field is big-endian and the decoder can read it with a plain move.w):
header, 32 bytes
0 'DLX1' magic
0 'DLX2' magic ('DLX1' = the same, unaligned; still read)
4 u16 width, u16 height
8 u16 fps, u16 nframes
12 u16 k1, u16 k4 codebook sizes
@@ -25,7 +25,9 @@ multi-byte field is big-endian and the decoder can read it with a plain move.w):
20 u32 cb1 offset (k1 * 16 bytes of palette indices)
24 u32 cb4 offset (k4 * 4 bytes)
28 u32 frames offset
then, per frame:
then, per frame, each record starting on a 4-BYTE BOUNDARY (0-3 zero pad
bytes before it; a 68000 takes an address error, not a slow read, on an odd
`move.l` -- FINDINGS 28.3):
u32 payload length, then
ceil(nblocks*2/8) bytes of 2-bit mode headers, MSB-first, block raster order
then payloads in block order: V1 -> 1 byte, V4 -> 4 bytes, RAW -> 16 bytes
@@ -83,7 +85,7 @@ def main():
global _IDX_BYTES
ap = argparse.ArgumentParser()
ap.add_argument("frames_dir"); ap.add_argument("out")
ap.add_argument("--profile", choices=list(RC.PROFILES), default="sasi")
ap.add_argument("--profile", choices=list(RC.PROFILES), default="scsi")
ap.add_argument("--lam", type=float, default=None)
ap.add_argument("--fps", type=int, default=12)
ap.add_argument("--iters", type=int, default=16)
@@ -165,19 +167,34 @@ def main():
off_cb1 = off_pal + len(pal_b)
off_cb4 = off_cb1 + len(cb1_b)
off_frm = off_cb4 + len(cb4_b)
hdr = (b"DLX1" + struct.pack(">HHHHHH", W_, H_, a.fps, len(idx), k1, k4)
# DLX2: every frame record starts on a 4-byte boundary, including the
# first. Payload lengths are arbitrary, so end-to-end records land on odd
# addresses -- and `move.l (a0)+` at an odd address is an ADDRESS ERROR on
# a 68000, not a slow read. It vectors into the IPL and looks exactly like
# an infinite loop (FINDINGS 28.3). tools/bench/prep_dlx.py has been
# realigning at load time; the container now carries it.
tbl_pad = -off_frm % 4
off_frm += tbl_pad
hdr = (b"DLX2" + struct.pack(">HHHHHH", W_, H_, a.fps, len(idx), k1, k4)
+ struct.pack(">IIII", off_pal, off_cb1, off_cb4, off_frm))
assert len(hdr) == 32, len(hdr)
frm_pad = 0
with open(a.out, "wb") as fh:
fh.write(hdr); fh.write(pal_b); fh.write(cb1_b); fh.write(cb4_b)
for p in frames:
fh.write(b"\0" * tbl_pad)
for i, p in enumerate(frames):
fh.write(struct.pack(">I", len(p))); fh.write(p)
if i + 1 < len(frames): # nothing follows the last record
n = -(4 + len(p)) % 4
fh.write(b"\0" * n); frm_pad += n
total = os.path.getsize(a.out)
vid = sum(len(p) + 4 for p in frames)
vid = sum(len(p) + 4 for p in frames) + frm_pad
print(f" wrote {a.out}: {total} B "
f"(header+tables {total-vid} B, video {vid} B)")
print(f" DLX2 4-byte record alignment: {frm_pad} B over {len(frames)} frames "
f"({frm_pad/len(frames):.2f} B/frame = {frm_pad/len(frames)*a.fps:.0f} B/s)")
print(f" {vid/len(idx):.0f} B/frame -> {vid/len(idx)*a.fps/1024:.1f} KB/s video"
f" + {RC.AUDIO_KBPS} KB/s audio = {vid/len(idx)*a.fps/1024+RC.AUDIO_KBPS:.1f} KB/s")
print(f" PSNR {r['psnr']:.2f} dB palette ceiling {r['pal']:.2f} dB "