microtimer is a fixed-capacity software timer manager for C99 projects.

It targets serialized access to one manager from one execution context by default. It does not provide heap allocation, hidden locks, persistence, or general ISR/thread safety.

• C99 and C11 consumers
• C++ header consumption
• GCC, Clang, and MSVC builds
• Main-loop usage
• ISR-owned usage with strict limits
• External synchronization around shared access
• ARM Cortex-M compile-only verification
• CMake find_package() and add_subdirectory() consumers

#include "mtimer.h"

static uint32_t app_clock_ms(void) { return platform_millis(); }

static void blink_cb(uint8_t id, void *ctx)
{
    (void)id;
    *(volatile int *)ctx = 1;
}

int main(void)
{
    mtimer_t tm;
    volatile int blink_due = 0;
    int timer_id;

    if (mtimer_init(&tm, app_clock_ms) != MTIMER_OK) {
        return 1;
    }

    timer_id = mtimer_create(&tm, "blink", 500u, MTIMER_PERIODIC, blink_cb, (void *)&blink_due);
    if (timer_id < 0) {
        return 1;
    }

    if (mtimer_start(&tm, (uint8_t)timer_id) != MTIMER_OK) {
        return 1;
    }

    for (;;) {
        int tick_rc = mtimer_tick(&tm);
        if (tick_rc < 0) {
            return 1;
        }
        if (blink_due) {
            blink_due = 0;
            toggle_led();
        }
    }
}

• Clock units are milliseconds on an unsigned 32-bit modulo counter.
• Natural uint32_t wraparound is supported if the clock is not reset while timers are active.
• mtimer_tick() fires each running timer at most once per successful call.
• Missed periodic intervals are skipped without callback bursts; phase is retained when only one interval is due.
• Timer names are optional and caller-owned. Non-NULL names must remain valid, immutable, and unique per manager.
• Timer IDs are slot indexes. Destroying a timer invalidates its ID, and later creates may reuse that slot.
• Same-manager mutation during callbacks returns MTIMER_ERR_BUSY.

cmake -S . -B build -DMICROTIMER_BUILD_TESTS=ON
cmake --build build
ctest --test-dir build --output-on-failure

make

Caller-provided CC, CPPFLAGS, CFLAGS, and LDFLAGS are honored by the Makefiles.

• API reference
• Cookbook
• Design notes
• Issues and troubleshooting
• Porting guide
• Verification status
• Contributing
• Security reporting
• Changelog

Releases are tag-driven through .github/workflows/release.yml and are only published from pushed v* tags.