Event pub/sub bus for embedded systems.

C99 | Zero dependencies | Zero allocations | ISR-safe queue | Portable

Without an event bus, modules call each other directly:

mfsm_dispatch(&fsm, EV_TEMP_HIGH);
MLOG_WARN("SENSOR", "overtemp");
iotspool_enqueue("alerts", cbor_buf, n);
mhealth_check_now(&hm);

With microbus, modules are decoupled:

mbus_publish(&bus, MBUS_TOPIC_SENSOR, &temp, sizeof(temp));

mbus_subscribe(&bus, MBUS_TOPIC_SENSOR, log_handler, NULL);
mbus_subscribe(&bus, MBUS_TOPIC_SENSOR, health_handler, &hm);
mbus_subscribe(&bus, MBUS_TOPIC_ANY, monitor_handler, NULL);

• Topic-based pub/sub with uint8_t topics
• Wildcard subscriber support (MBUS_TOPIC_ANY)
• Fixed-size payload (default: 32 bytes, configurable)
• Synchronous publish (mbus_publish)
• Deferred ISR-safe queue (mbus_queue + mbus_dispatch)
• Signal events (mbus_signal, mbus_queue_signal)
• Unsubscribe by index and by topic
• Slot reuse after unsubscribe
• Built-in counters (publish, deliver, drop)

#include "mbus.h"

void on_sensor(const mbus_event_t *e, void *ctx) {
    (void)ctx;
    float temp;
    memcpy(&temp, e->payload, sizeof(temp));
}

mbus_t bus;
mbus_init(&bus, HAL_GetTick);
mbus_subscribe(&bus, MBUS_TOPIC_SENSOR, on_sensor, NULL);

float temp = 23.5f;
mbus_publish(&bus, MBUS_TOPIC_SENSOR, &temp, sizeof(temp));

Requirements:

• GCC (or compatible C99 compiler)
• make
• microtest header in ../../microtest/include/mtest.h relative to tests/

Run tests:

cd tests
make

• include/mbus.h - public API
• src/mbus.c - implementation
• tests/test_all.c - unit tests
• docs/DESIGN.md - design rationale
• CHANGELOG.md - release notes
• CONTRIBUTING.md - contribution rules

MIT, see LICENSE.