[kammce]

Closes #109. Depends on libhal/libhal#252, which adds hal::can_receive_filter to can_interrupt::on_receive(). This PR's CI needs libhal/5.0.0-alpha.5, which #252 cuts when it merges.

hal::can_interrupt_dispatcher<N> lets several subscribers share one hal::can_interrupt, which in libhal v5 accepts a single subscriber. Each subscriber passes its own filter when it subscribes, the same as with a real interrupt, so whoever wires up the dispatcher doesn't need to know any driver's IDs.

hal::can_interrupt_dispatcher<2> dispatcher(can_interrupt);
motor_controller motor(dispatcher[0]);  // subscribes with { .id = 0x120, .mask = 0x1FFF'FFFF }
bus_logger logger(dispatcher[1]);       // subscribes for every message

Behavior

• Subscribes once to the real interrupt, for every message.
• Each slot is a full hal::can_interrupt with one subscriber. A second subscriber throws hal::subscription_busy.
• Every dispatcher size uses one slot type, hal::can_interrupt_slot, so dispatcher<2> and dispatcher<7> don't each instantiate their own slot class and vtable. Its constructor is private: only a dispatcher creates slots.
• Filtering: each slot stores the hal::can_receive_filter its subscriber passed to on_receive(). The filter is { id, mask } from libhal.
  • A message passes when (message.id & mask) == (id & mask). It compares IDs only, so one filter works for standard and extended messages.
  • The default (mask 0) passes every message.
  • A new subscriber brings its own filter, replacing the previous subscriber's.
• On each received message, calls every subscribed slot whose filter passes it, in slot order, in interrupt context: O(N) per message.
• A compiler-only fence (std::atomic_signal_fence) keeps the filter written before the callback that makes the slot live, since the interrupt reads them in that order. It emits no instructions and isn't std::atomic.
• This filters in software, after any hardware filter, so it only sees messages the hardware already accepted.
• Same structure and lifetime rules as edge_triggered_interrupt_dispatcher (✨ v6: Add edge_triggered_interrupt_dispatcher #110):
  • lifetimebound constructor parameter and operator[], with operator[] deleted on a temporary;
  • not copyable or movable;
  • the subscription to the real interrupt is declared last.

Tests

• tests/can.test.cpp:
  • subscribing and unsubscribing, and subscription_busy on a taken interrupt;
  • delivery to every subscribed slot, and one subscriber per slot;
  • out_of_range;
  • the dispatcher subscribing to the real interrupt for every message;
  • subscriber filters (a block of IDs, an exact ID, the default);
  • one filter across standard and extended IDs;
  • a new subscriber replacing the previous filter.
• Compile checks, added to the files from ✨ v6: Add edge_triggered_interrupt_dispatcher #110: the same rejected and lifetime-analysis cases as the edge-triggered dispatcher.

Testing

macOS, LLVM 23, against libhal built locally from libhal/libhal#252 (as libhal/latest, via replace_requires): all 16 test suites pass, and both compile-check files pass.

[kammce]

lgtm