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fix(nfc): auto-recover a wedged CCID reader via USB power-cycle

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The Feitian R502-CL (and cheap CCID readers generally) can wedge: it keeps
detecting a card but every APDU returns "card absent or mute", and ONLY a
USB power-cycle clears it — restarting pcscd or the app does not (confirmed
on-device). Until now that left cash-out/cash-in taps dead until a manual
replug.

- nfc-service.ts: count consecutive read failures; after 3 (gated by a 30s
  cooldown so a still-wedged reader can't reset-loop) trigger
  nfc-reader-reset.service. nfc-pcsc then re-detects the reader on USB
  hotplug with no app restart (verified live).
- batm3.nix: nfc-reader-reset.service (oneshot, root) re-binds the reader's
  USB device (a software replug); reader-agnostic via the CCID interface
  class (0x0B) so it also covers a future ACR1252U. A polkit rule lets the
  unprivileged `bitspire` app start just that one unit.

Hardware track (separate): the durable fix is a better reader (ACR1252U —
large antenna for behind-panel, firmware-upgradable). This change makes any
reader's wedge a ~2s self-heal in the meantime.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
This commit is contained in:
Patrick Mulligan 2026-08-06 19:51:39 +02:00
commit ffbacafe39
2 changed files with 96 additions and 4 deletions
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42
deploy/nixos/hardware/batm3.nix
View file

@ -94,7 +94,8 @@
# pcscd gates client access via polkit; without a rule the sandboxed
# `bitspire` service user is "Rejected unauthorized PC/SC client". Authorize
# it to talk to the daemon and the card.
# it to talk to the daemon and the card. The second rule lets the app trigger
# the NFC reader wedge-recovery service (see nfc-reader-reset below).
security.polkit.extraConfig = ''
polkit.addRule(function(action, subject) {
if ((action.id == "org.debian.pcsc-lite.access_pcsc" ||
@ -103,8 +104,47 @@
return polkit.Result.YES;
}
});
polkit.addRule(function(action, subject) {
if (action.id == "org.freedesktop.systemd1.manage-units" &&
action.lookup("unit") == "nfc-reader-reset.service" &&
subject.user == "bitspire") {
return polkit.Result.YES;
}
});
'';
# NFC reader wedge-recovery. The Feitian R502-CL CCID reader (and, less often,
# any CCID reader) can wedge: it keeps detecting a card but every APDU returns
# "card absent or mute", and ONLY a USB power-cycle clears it — restarting
# pcscd or the app does not. This oneshot re-binds the reader's USB device (a
# software replug); pcscd + nfc-pcsc then re-detect it on hotplug with no app
# restart (verified on-device). The app (unprivileged `bitspire`) starts it via
# the polkit rule above when it sees repeated read failures. Reader-agnostic:
# it matches the USB CCID interface class (0x0B), so it also covers a future
# ACR1252U swap without a config change.
systemd.services.nfc-reader-reset = {
description = "Power-cycle a wedged CCID NFC reader (USB re-bind)";
serviceConfig = {
Type = "oneshot";
ExecStart = pkgs.writeShellScript "reset-nfc-reader" ''
set -u
found=0
for iface in /sys/bus/usb/devices/*:*/bInterfaceClass; do
[ -f "$iface" ] || continue
[ "$(${pkgs.coreutils}/bin/cat "$iface" 2>/dev/null)" = "0b" ] || continue
ifname=$(${pkgs.coreutils}/bin/basename "$(${pkgs.coreutils}/bin/dirname "$iface")")
dev=''${ifname%%:*}
echo "reset-nfc-reader: power-cycling CCID reader USB device $dev" >&2
echo -n "$dev" > /sys/bus/usb/drivers/usb/unbind 2>/dev/null || true
${pkgs.coreutils}/bin/sleep 2
echo -n "$dev" > /sys/bus/usb/drivers/usb/bind 2>/dev/null || true
found=1
done
[ "$found" = 1 ] || { echo "reset-nfc-reader: no CCID reader found" >&2; exit 1; }
'';
};
};
# Disable suspend/hibernate for kiosk
systemd.targets = {
sleep.enable = false;