# Hardware notes

Things about specific hardware that cost time to work out. Kept out of the README
because they are not install steps.

## Screen size and rack size are different measurements

Three numbers get confused because they all describe "how big":

- **9 inch** — the GeeekPi touchscreen itself, 1280x720.
- **10 inch** — the *mini-rack* standard its bracket is made for.
- **19 inch** — the standard equipment rack, which is what `cad/` adapts it to.

So "a 9-inch screen on a 10-inch mount, adapted to a 19-inch rack" is three
correct numbers, not a contradiction. The README uses the screen size when
talking about the panel and the rack size when talking about the adapter.

## The ILITEK panel reports 2-3 contacts for one finger

A physically one-finger swipe arrives as two, sometimes three, simultaneous
contacts. In v1 this was the single most expensive failure: lisgd detected the
direction correctly every time and then rejected it on
`Cfg(f=1) <=> Evt(f=2)`, which reads as noise unless you know what it means.

`touch.fingers: [1, 2, 3]` accepts all three. `socktop-swipe doctor` now reports
it in English, and the travel is *averaged* across contacts rather than summed —
otherwise a ghost-contact panel looks like it swiped three times as far.

## Phantom display outputs (LattePanda DSI-1)

The LattePanda's onboard DSI header shows up as `DSI-1 connected 1024x600` with
**zero EDID bytes** (`xrandr` reports `0mm x 0mm`), and X happily puts workspace 1
on it. Everything then looks healthy over ssh — the window is fullscreen on the
primary output — while the real panel shows an empty workspace.

```sh
xrandr | grep ' connected'      # a real panel has physical mm; phantoms say 0mm x 0mm
for c in /sys/class/drm/card0-*; do echo "$c $(cat "$c"/status) edid=$(wc -c <"$c"/edid)"; done
```

Fix, adjusting the names:

```sh
sudo tee /etc/X11/xorg.conf.d/20-outputs-socktop-swipe.conf >/dev/null <<'EOF'
Section "Monitor"
    Identifier "DSI-1"
    Option     "Ignore" "true"
EndSection
Section "Monitor"
    Identifier "HDMI-2"
    Option     "Primary" "true"
EndSection
EOF
```

Then set `touch.width`/`touch.height` to the real panel's mode. On the LattePanda
that is **1280x720**, not the 1024x600 the phantom claims.

## `sudo xset` silently does nothing

`xset` talks to the X connection of the user running it, so `sudo xset s off`
targets *root's* X connection and succeeds while changing nothing for your
session. A `sudo bash noblank.sh` wrapper looks like it worked and blanking stays
armed. It must run as the session user.

Also: `xset` is per-session and dies on reboot. The durable fix is the Xorg
`ServerFlags` snippet with all four timeouts at 0 — which also covers the display
manager's greeter — *plus* an `xset` line in the session autostart, because a
session can re-enable the screensaver after X starts. Both, not either.

Check the real state:

```sh
xset q | grep -A1 -E 'Screen Saver|DPMS'   # want timeout 0, prefer blanking no, DPMS Disabled
```

## Panel resolution is not the X screen size

With a second display attached, X reports the combined root window (e.g.
2304x720). `touch.width`/`touch.height` must describe the touch panel alone or
the edge and distance maths is scaled to the wrong thing. v1 hit this because
lisgd asks X when not told; v2 always requires the values in the config.

## LattePanda specifics

Atom x5-Z8350 @ 1.44 GHz, 1.9 GB RAM, Cherry Trail Gen8 graphics, Debian 11,
i3 on X11. Binaries in `~/.cargo/bin`, which is **not** on the PATH that i3 or a
non-login ssh gives you — hence the `binaries:` block in the config.

Memory is the binding constraint. Prefer the lightweight option and count
processes; reach for tmux pane zoom rather than duplicate program instances. A
Wayland compositor with native touch gestures is not an answer here: Hyprland is
not packaged in Debian, so it means a source build on a 1.44 GHz Atom, and it
would not help anyway — libinput emits no gesture events for touchscreens on any
version, so a raw-touch reader is required regardless.

## Wyse 3040

Same silicon as the LattePanda (Atom x5-Z8350, Cherry Trail), so the stack is
already validated. Differences: 8/16 GB soldered eMMC and no M.2, so a minimal
Debian netinst and a careful eye on disk; DisplayPort out, so a DP-to-HDMI
adapter for the panel; roughly 3-4 W idle, 101x101x28 mm, VESA holes.

The eMMC is why the installer checks free space before starting a build: a Rust
toolchain plus a target directory is around 1.8 GB.

## Never log out of a keyboard-less wall display

lightdm autologin fires when a **seat starts**, not after a logout. `i3-msg exit`
therefore drops the display to the greeter and leaves it there — and the rack
panel has no keyboard, so nobody can log back in at the machine. Recovering it
needs `sudo systemctl restart lightdm` or a reboot, and the LattePanda has no
passwordless sudo.

So: **`i3-msg exit` does not test the autostart, it only strands the box.** The
only honest test of the boot path is an actual reboot.

Related trap when handing over a root command: `ssh host 'sudo …'` allocates no
TTY, so sudo has nowhere to prompt and fails. Use `ssh -t`. Chaining with `&&`
then swallows the rest of the line, which is how a recovery command silently did
nothing at all. Use `;` for recovery steps that must run regardless.