While copying, ft-eyegrab woke every 300 us (about 1,500 to 3,000 times a second) and
fingerprinted all eight slots each time: 8 x 256 strided reads from DMA-BUF memory.
- Each look now checks only the slot each camera writes next. The order is known (camera 0
3,0,1,2; camera 1 7,5,4,6,5,7,6,4), and the next slot follows from the last two; the table
starts from those orders and learns from every frame, so a SteamVR update that changes
them costs a few seconds of full scans, not frames.
- A camera with nothing in its expected slot 1.5 frames after its last one, or with no
order yet, gets all four slots checked, as before. A frame that turns up in an unexpected
slot means full scans for that camera for 2 s.
- A slot's fingerprint is taken again when it stops being one of the two in use, so a later
check sees only a new frame. A frame is still passed on when its camera starts the frame
after next.
- Between frames it sleeps until 2.5 ms before the next is due, then looks every 1 ms, with
0.5 ms of timer slack (PR_SET_TIMERSLACK, --share only). With no frames from either
camera for 0.5 s (headset off) it looks every 4 ms.
- --rec keeps its 0.3 ms polls (and the expected-slot checks), for its timestamps.
Tested offline by building poll_frames against simulated cameras that write each frame in
four bursts, the last after the next frame starts (6 s, both cameras): 1,076 frames passed
on, none torn or skipped, with the known orders and with camera 1 in a different order.
Wakeups 1,486/s -> 207/s, the poller's CPU 3.6% -> 0.8% of a core (in plain memory; the real
DMA-BUF reads cost more), and a frame's start is seen 1.35 ms after it begins on average
instead of 0.76. With a camera stalling 15 ms every 2 s, the old poller passed on 22 torn
frames and the new one 8 or fewer.
Built (glibc 2.38 symbols at most, the host has 2.39), not installed: it runs as root from
/etc/frametop, so it takes effect only after gaze/tracker/install.sh (sudo).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
frame-eyes, a separate project until now, becomes gaze/tracker:
- ft-eyegrab (was fe-bufprobe) copies the eye-camera frames, read-only, out of
SteamVR's eyetracking process. It runs as the system service
frametop-eyegrab.service, which gaze/tracker/install.sh installs to
/etc/frametop with sudo. It keeps only CAP_SYS_PTRACE, CAP_DAC_READ_SEARCH, and
CAP_CHOWN, and copies frames only while /dev/shm/frametop-eyes-want is fresh,
holding none of the tracker's buffers otherwise.
- ft-eyes (was fe-trackd) runs under ft-gazed in the dev container, with
build/venv's pinned numpy and OpenCV: while Eye tracker is Own tracker, or on
the probe's lease ("eyes SECONDS"). No sudo password or fe-live script at
run time any more.
- lab/ holds the research tools (ft-eyes-score, -e2e, -record, -replay,
-session) and findings.md. Recordings live outside the repo, in
~/.local/share/frametop/eyes/captures; .gitignore catches stray frame dumps.
Its socket is now @ft_eyes, its output /dev/shm/frametop-eyes-gaze, and its state
~/.local/state/frametop/gaze/eyes. On practice1 -> practice2 the whole live path
(ft-eyes-e2e) gives 1.30 deg median and 3.18 for the worst tenth, as before the
move (1.30, 3.21).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
