pympacds-gpio

GPIO server service for pympacds. Monitors GPIO line state and edge events and exposes reads, writes, and change notifications over D-Bus.

Features

• Reads (get_value, get_lines) and writes (set_value) of GPIO lines over D-Bus, with per-output-line default (reset) values (get_default_value / set_default_value).
• Edge-event watching (line_changed signal) driven by the kernel gpiod edge-event API, polled asynchronously with a short timeout so the event loop is never stalled.
• Kernel-side debounce via debounce_us (passed to libgpiod), and active_low inversion for watched lines. No software debounce.
• A configurable line-name mapping ([gpio.linemap]) so lines can be referenced by human-readable name or numeric offset on the D-Bus API.
• Runtime configuration: [gpio] keys are writable via the framework ConfigContract.
• Exports the framework HealthContract (always) and ConfigContract (opt-in via [dbus] contract_config = true) alongside the GPIO contract.

Why gpiod

The service uses the gpiod Python bindings (libgpiod v2 API) because it is the reference userspace interface to the kernel GPIO character-device subsystem: line requests, edge events, and debounce are all handled in the kernel. It is isolated in this service's own package, so the core pympacds framework keeps its zero-dependency property.

Installation

pip install pympacds-gpio

Configuration

The service reads its parameters from the [gpio] INI section and the optional [gpio.linemap] section (see config/gpio.ini.example):

The [gpio.linemap] section maps human-readable names to offsets (btn = 0). Names must not begin with a digit.

Run with:

pympacds-gpio -c /etc/pympacds/gpio.ini

Device access (permissions)

The service does not require root. Access to /dev/gpiochip* is granted via a udev rule (shipped by the Debian package) that assigns the device to the gpio group with mode 0660; add the service user to the gpio group:

sudo usermod -aG gpio <service-user>

D-Bus API

Interface org.pympacds.GPIO at object path /org/pympacds/gpio:

A line argument is a decimal offset or a [gpio.linemap] name, resolved number-first-then-name. An unresolvable line produces a D-Bus error reply.

The framework HealthContract (at .../health) and ConfigContract ([dbus] contract_config = true) are also exported.