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Put the ring on the 68000, and find the disc stops whenever the player is not asking

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ROADMAP P5. The loader moved in session 21 and the frame clock in 22; the ring
producer was the last policy living outside the machine. src/player/ring.i does
`aligned` placement, the descriptor ring, a prefill, 51.2's slack rule and a
seek, and the host keeps only the transport.

It needed a container change. `aligned` asks whether the next record fits
before the end of the ring -- a length asked BEFORE the record is fetched -- and
every reader in this tree answered that by walking the frame stream, which is
exactly what a player streaming off a disc cannot do. DLX4 carries nframes u16
record lengths in the scene header. Frame payloads are byte-identical to the
DLX3 encode, so no fitted constant moves; the scene header goes 5,920 to 6,164 B.

The producer reproduces the host's tiling exactly: 18 wraps, 14.7 KB mean hole,
pixel-exact, a third independent implementation of the same policy.

What it exposed is bigger than the item. A channel only moves bytes while it has
a request and only the CPU can issue one, so the disc stands still between
records by an amount the PLAYER sets, not the medium -- and no host-filled run
could see it. At 488 KB/s in a 256 KB ring a one-deep request queue gives away
6.8% of the pipe and underruns 59 of 120 frames; two-deep gives away 3.4% and
underruns none. The container's whole surplus over the wire is 8.7%, so the
player's own loop was spending most of the slack a branch point saves up.
Prefill is the weaker lever: six records of it still leaves 24 underruns.

Three silent bugs are recorded in FINDINGS 55.7 -- all produced wrong pixels or
a desync rather than a fault -- plus a rig one: MAME renders a screen line by
line, so snapshotting the frame the decoder finished in captures a tear that
reads exactly like a decoder bug.

check.sh gains the machine-owned ring and a seek with the decode after it.
decode.bin is unchanged at 1,296 B and a host-filled run executes none of the
new code, so every FINDINGS 49/51 figure stands. ALL GREEN before and after.

Claude-Session: https://claude.ai/code/session_01194oWYW8DQXK1SZ2DnChW6
This commit is contained in:
prosolis
2026-08-24 21:45:05 -07:00
parent c419251266
commit 2676f3b835
16 changed files with 1880 additions and 38 deletions
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tools/bench/pace_run.sh
+25 -1
View File
@@ -16,6 +16,18 @@
# kbps 0 = unlimited pipe. There is no default rate anywhere in this tree
# (FINDINGS 50) and there is none here either.
#
# DLX_RINGOWN=1 hands the RING to the 68000 as well (ROADMAP P5,
# src/player/ring.i): this script's Lua stops placing records and becomes a
# transport that answers one request at a time. DLX_PREFILL_FR is then the
# prefill policy, in whole records. It needs a DLX4 container, because the
# machine cannot learn a record's length by walking a stream it has not fetched.
#
# DLX_ITER=2 runs the scene TWICE, which under DLX_RINGOWN means a real seek
# between the passes: the channel goes quiet, the ring is declared empty and the
# whole accumulated lookahead is thrown away and rebuilt from the prefill. It
# needs DLX_PACE=2, because rebasing the frame clock across a pass is the
# machine's to do and a host-written tick would carry on counting.
#
# DLX_PACE selects WHO KEEPS THE TIME: 1 (default) is the host writing the tick,
# 2 is the 68000 writing it off the CRTC's V-DISP (ROADMAP P3, FINDINGS 54).
# Everything else about the run is identical, which is the whole point -- the
@@ -27,11 +39,21 @@ RING=${1:?ring KB}; KBPS=${2:?pipe KB/s, or 0 for unlimited}
CUT_AT=$3; CUT_FR=${4:-1}
DLX=${DLX:-tmp/rc_fr_singe_scsi_span.dlx}
PACE=${DLX_PACE:-1}
OWN=${DLX_RINGOWN:-0}
ITERS=${DLX_ITER:-1}
if [ "$OWN" = 1 ] && [ "$ITERS" != 1 ] && [ "$PACE" != 2 ]; then
echo "DLX_ITER>1 needs DLX_PACE=2: the frame clock is rebased per pass by"
echo "src/player/stream.s, and a host-written tick would go on counting"
echo "through the seek and open every slot of the second pass at once."
exit 2
fi
TAG="r${RING}_k${KBPS}${CUT_AT:+_cut${CUT_AT}x${CUT_FR}}"
# The default tag is left ALONE when the host keeps the time: tools/bench/
# pace_sweep.sh reads tmp/pace_r<ring>_k<kbps>.log by name, and renaming the
# host-paced logs would break a sweep that has nothing to do with this option.
if [ "$PACE" != 1 ]; then TAG="${TAG}_p$PACE"; fi
if [ "$OWN" = 1 ]; then TAG="${TAG}_own"; fi
if [ "$ITERS" != 1 ]; then TAG="${TAG}_x$ITERS"; fi
tools/vasm/vasmm68k_mot -Fbin -o tmp/stream.bin src/player/stream.s > /dev/null
[ -f tmp/stream_disk.bin ] || python3 tools/bench/prep_stream.py "$DLX" > tmp/prep_stream.log
@@ -41,6 +63,8 @@ mkdir -p "tmp/snap_pace_$TAG"; rm -f "tmp/snap_pace_$TAG/x68000"/*.png
# command and the run dies with "SDL_VIDEODRIVER=dummy: command not found".
CUTENV=(); [ -n "$CUT_AT" ] && CUTENV=(DLX_CUT_AT="$CUT_AT" DLX_CUT_FR="$CUT_FR")
( cd tmp && env DLX_PACE=$PACE DLX_RING_KB=$RING DLX_STREAM_KBPS=$KBPS \
DLX_RINGOWN=$OWN DLX_ITER=$ITERS \
${DLX_PREFILL_FR:+DLX_PREFILL_FR=$DLX_PREFILL_FR} \
"${CUTENV[@]}" DLX_SLACK_CSV="slack_$TAG.csv" \
SDL_VIDEODRIVER=dummy stdbuf -oL timeout -k 5 900 \
mame x68000 -bios ipl10 -ramsize 2M -video soft -window -sound none \
@@ -53,6 +77,6 @@ grep -q "snapshot taken" "tmp/pace_$TAG.log" || {
echo "FAIL($TAG): no snapshot marker -- the pass did not complete."
tail -6 "tmp/pace_$TAG.log"; exit 1; }
echo "=== $TAG"
grep -aE "decoder (SELF-PACED|PACED|FREE)|FRAME CLOCK|ring: |UNDERRUNS|NO IDLE|SEEK SLACK|RING-BOUND|RATE-BOUND|BUILD TIME|PIPE CUT|DEADLINE|REQUIRED" \
grep -aE "decoder (SELF-PACED|PACED|FREE)|FRAME CLOCK|ring: |UNDERRUNS|NO IDLE|SEEK SLACK|RING-BOUND|RATE-BOUND|BUILD TIME|PIPE CUT|DEADLINE|REQUIRED|MACHINE-OWNED|PREFILL:|CHANNEL IDLE|MISPLACED|SEEK PASS" \
"tmp/pace_$TAG.log" | sed "s/\[STR\] / /"
python3 tools/bench/verify_decode.py "$DLX" --snap "tmp/snap_pace_$TAG" | tail -2