Show HN: TinyOS – A minimalist RTOS for Cortex-M written in C - News

make example-blink    # LED blink
make example-shell    # Interactive shell over UART
make example-mqtt     # MQTT publish/subscribe
make example-iot      # Multi-sensor IoT node
make size             # Binary size report

#include "tinyos.h"

void my_task(void *param) {
    while (1) {
        /* work */
        os_task_delay_ms(100);
    }
}

int main(void) {
    tcb_t task;
    os_init();
    os_task_create(&task, "my_task", my_task, NULL, PRIORITY_NORMAL);
    os_start();
}

os_task_create(tcb, name, entry, param, priority)
os_task_delete(task)
os_task_suspend(task) / os_task_resume(task)
os_task_delay(ticks) / os_task_delay_ms(ms)
os_task_set_priority(task, priority)
os_task_get_stats(task, stats)
os_task_get_stats_by_index(index, stats)   /* iterate all tasks by index */
os_task_find_by_name(name)                 /* returns tcb_t*, NULL if not found */
os_get_system_stats(stats)
os_get_memory_stats(&free, &used, &allocs, &frees)

os_mutex_init(mutex) / os_mutex_lock(mutex, timeout) / os_mutex_unlock(mutex)
os_semaphore_init(sem, count) / os_semaphore_wait(sem, timeout) / os_semaphore_post(sem)
os_cond_init(cond) / os_cond_wait(cond, mutex, timeout)
os_cond_signal(cond) / os_cond_broadcast(cond)
os_event_group_set_bits(eg, bits) / os_event_group_wait_bits(eg, bits, opts, out, timeout)
os_queue_init(q, buf, item_size, max) / os_queue_send(q, item, timeout)
os_queue_receive(q, item, timeout) / os_queue_peek(q, item, timeout)

os_timer_create(timer, name, type, period_ms, callback, param)
os_timer_start(timer) / os_timer_stop(timer) / os_timer_reset(timer)
os_timer_change_period(timer, ms) / os_timer_get_remaining_ms(timer)

/* Register custom commands before calling shell_start() */
shell_register_cmd(name, handler_fn, help_text)

/* Provide UART I/O callbacks and start the shell task */
shell_io_t io = { .getc = uart_getc, .puts = uart_puts };
shell_start(&io)

/* Change the prompt at any time */
shell_set_prompt("mydevice> ")

/* Execute a single line programmatically */
shell_exec(line)

static int cmd_led(int argc, char *argv[]) {
    if (argc < 2) return 1;  /* non-zero → prints usage */
    bool on = (strcmp(argv[1], "on") == 0);
    gpio_write(LED_PIN, on);
    return 0;
}

/* In main(), before shell_start(): */
shell_register_cmd("led", cmd_led, "led <on|off>  Toggle LED");

#define SHELL_MAX_COMMANDS   32    /* max registered commands       */
#define SHELL_LINE_MAX       128   /* max input line length (bytes) */
#define SHELL_ARGV_MAX       16    /* max arguments per command     */
#define SHELL_HISTORY_DEPTH  8     /* command history entries       */

net_init(driver, config) / net_start()
net_socket(type) / net_bind(sock, addr) / net_connect(sock, addr, timeout_ms)
net_send(sock, data, len, timeout_ms) / net_recv(sock, buf, len, timeout_ms)
net_sendto(sock, data, len, addr) / net_recvfrom(sock, buf, len, addr)
net_close(sock)
net_ping(dest_ip, timeout_ms, rtt)
net_dns_resolve(hostname, ip, timeout_ms)
net_http_get(url, response, timeout_ms)
net_http_post(url, content_type, body, len, response, timeout_ms)

/* Client (TLS over TCP) */
tls_context_t tls;
tls_config_t  cfg = TLS_CONFIG_DEFAULT_CLIENT;
cfg.ca_cert     = ca_cert_pem;
cfg.ca_cert_len = sizeof(ca_cert_pem);
tls_init(&tls, &cfg);

net_socket_t sock = net_socket(SOCK_STREAM);
net_connect(sock, &broker_addr, 5000);
tls_connect(&tls, sock, "example.com", 5000);

tls_send(&tls, data, len);
tls_recv(&tls, buf, sizeof(buf), 5000);
tls_close(&tls);

/* Server (TLS accept) */
tls_config_t srv_cfg = TLS_CONFIG_DEFAULT_SERVER;
srv_cfg.cert     = server_cert_pem;
srv_cfg.cert_len = sizeof(server_cert_pem);
srv_cfg.key      = server_key_pem;
srv_cfg.key_len  = sizeof(server_key_pem);
tls_init(&tls, &srv_cfg);
tls_accept(&tls, client_sock, 5000);

/* DTLS over UDP */
tls_config_t dtls_cfg = TLS_CONFIG_DEFAULT_DTLS_CLIENT;
net_socket_t usock = net_socket(SOCK_DGRAM);
tls_connect_dtls(&tls, usock, "example.com", 5000);

mqtt_config_t cfg = {
    .broker_host          = "mqtt.example.com",
    .client_id            = "tinyos-01",
    .keepalive_sec        = 60,
    .clean_session        = true,
    .auto_reconnect       = true,
    .reconnect_interval_ms = 3000,   /* base; doubles each attempt (max 60 s) */
};
mqtt_client_t client;
mqtt_client_init(&client, &cfg);
mqtt_set_connection_callback(&client, on_connect, NULL);
mqtt_set_message_callback(&client, on_message, NULL);
mqtt_connect(&client);

/* Publish — QoS1/2 are buffered offline if disconnected */
mqtt_publish(&client, "sensors/temp", "23.5", 4, MQTT_QOS_1, false);

/* Inspect reliability queues */
uint8_t in_flight = mqtt_get_inflight_count(&client);  /* sent, awaiting ACK  */
uint8_t pending   = mqtt_get_pending_count(&client);   /* queued while offline */

mqtt_subscribe(&client, "cmd/#", MQTT_QOS_1);
mqtt_flush_pending(&client);   /* discard offline queue */
mqtt_disconnect(&client);

QoS 0  ─── fire-and-forget; dropped if disconnected
QoS 1  ─── in-flight table tracks each PUBLISH until PUBACK
              ↳ retransmits with DUP=1 every 5 s, up to 5 times
              ↳ if offline → offline queue (up to 8 messages)
QoS 2  ─── full PUBLISH → PUBREC → PUBREL → PUBCOMP handshake
              ↳ each step is retried independently on timeout

Auto-reconnect back-off: 3 s → 6 s → 12 s → … → 60 s (cap)
On reconnect: re-subscribes all topics, flushes offline queue

#define MQTT_MAX_INFLIGHT          8      /* in-flight slots       */
#define MQTT_MAX_PENDING           8      /* offline queue slots   */
#define MQTT_MAX_PAYLOAD_SIZE      512    /* bytes per queued msg  */
#define MQTT_RETRY_INTERVAL_MS     5000   /* retry after (ms)      */
#define MQTT_MAX_RETRY_COUNT       5      /* retries before drop   */
#define MQTT_RECONNECT_BASE_MS     3000   /* first reconnect delay */
#define MQTT_RECONNECT_MAX_MS      60000  /* backoff ceiling       */

coap_init(ctx, config, is_server) / coap_start(ctx) / coap_stop(ctx)
coap_get(ctx, ip, port, path, response, timeout_ms)
coap_post(ctx, ip, port, path, format, payload, len, response, timeout_ms)
coap_resource_create(ctx, path, handler, user_data)
coap_process(ctx, timeout_ms)

ota_init(config)
ota_start_update(url, callback, user_data)
ota_write_chunk(data, size, offset) / ota_finalize_update()
ota_confirm_boot() / ota_rollback()
ota_verify_partition(type)

fs_format(device) / fs_mount(device) / fs_unmount()
fs_open(path, flags) / fs_close(fd)
fs_read(fd, buf, size) / fs_write(fd, buf, size)
fs_seek(fd, offset, whence) / fs_tell(fd)
fs_mkdir(path) / fs_remove(path) / fs_rmdir(path)
fs_stat(path, stat)
fs_opendir(path) / fs_readdir(dir, entry) / fs_closedir(dir)
fs_get_stats(stats) / fs_get_free_space() / fs_is_mounted()

os_power_init()
os_power_set_mode(mode)          /* ACTIVE / IDLE / SLEEP / DEEP_SLEEP */
os_power_get_mode()
os_power_enter_sleep(duration_ms)
os_power_enter_deep_sleep(duration_ms)
os_power_enable_tickless_idle(enable)
os_power_set_cpu_frequency(freq_hz)
os_power_configure_wakeup(source, enable)
os_power_get_stats(stats)
os_power_get_consumption_mw()
os_power_estimate_battery_life_hours()

wdt_init(config) / wdt_start() / wdt_stop()
wdt_feed() / wdt_set_timeout(ms)
wdt_register_task(task, timeout_ms) / wdt_feed_task(task)

#define MAX_TASKS        8      /* max concurrent tasks           */
#define STACK_SIZE       256    /* stack size per task (words)    */
#define TICK_RATE_HZ     1000   /* scheduler tick frequency (Hz)  */
#define TIME_SLICE_MS    10     /* round-robin time slice (ms)    */

#define SHELL_MAX_COMMANDS   32   /* max registered commands         */
#define SHELL_LINE_MAX       128  /* max input line length (bytes)   */
#define SHELL_ARGV_MAX       16   /* max arguments per command       */
#define SHELL_HISTORY_DEPTH  8    /* command history ring buffer     */

#define MQTT_MAX_INFLIGHT        8      /* in-flight QoS1/2 slots    */
#define MQTT_MAX_PENDING         8      /* offline queue slots       */
#define MQTT_MAX_PAYLOAD_SIZE    512    /* max queued payload bytes  */
#define MQTT_RETRY_INTERVAL_MS   5000   /* unACKed retry interval    */
#define MQTT_MAX_RETRY_COUNT     5      /* retries before discard    */
#define MQTT_RECONNECT_BASE_MS   3000   /* initial reconnect delay   */
#define MQTT_RECONNECT_MAX_MS    60000  /* back-off ceiling          */

CFLAGS += -DTINYOS_TLS_ENABLE
LDFLAGS += -lmbedtls -lmbedcrypto -lmbedx509

tinyos-rtos/
├── include/
│   ├── tinyos.h              # Core API (tasks, sync, timers, memory, FS, power)
│   └── tinyos/
│       ├── shell.h           # Interactive shell API & configuration
│       ├── net.h             # Network stack
│       ├── tls.h             # TLS 1.2/1.3 + DTLS 1.2 (mbedTLS)
│       ├── mqtt.h            # MQTT 3.1.1 client
│       ├── coap.h            # CoAP RFC 7252
│       ├── ota.h             # OTA firmware updates
│       └── watchdog.h        # Watchdog timer
├── src/
│   ├── kernel.c              # Preemptive scheduler & task management
│   ├── sync.c                # Mutex, semaphore, queue, condition var, event groups
│   ├── timer.c               # Software timers
│   ├── memory.c              # Heap allocator
│   ├── shell.c               # Interactive shell (VT100, history, tab completion)
│   ├── filesystem.c          # Block-device file system
│   ├── security.c            # MPU memory protection
│   ├── power.c               # Power management & CPU frequency scaling
│   ├── watchdog.c            # Watchdog (HW + SW, per-task monitoring)
│   ├── bootloader.c          # Secure bootloader
│   ├── ota.c                 # OTA A/B partition updates
│   ├── mqtt.c                # MQTT client (in-flight table, offline queue)
│   ├── coap.c                # CoAP client/server
│   └── net/
│       ├── network.c         # Core & buffer management
│       ├── ethernet.c        # Ethernet / ARP
│       ├── ip.c              # IPv4 / ICMP
│       ├── socket.c          # UDP / TCP socket API
│       ├── http_dns.c        # HTTP client & DNS resolver
│       └── tls.c             # TLS/DTLS (mbedTLS wrapper)
├── drivers/
│   ├── flash.c / flash.h     # Flash memory driver
│   ├── ramdisk.c / ramdisk.h # RAM disk (testing)
│   └── loopback_net.c        # Loopback network driver (testing)
└── examples/
    ├── blink_led.c           # GPIO blink
    ├── iot_sensor.c          # Multi-task sensor node
    ├── shell_demo.c          # Custom shell commands over UART
    ├── network_demo.c        # TCP/UDP/HTTP/ping
    ├── tls_demo.c            # TLS client/server
    ├── mqtt_demo.c           # MQTT publish/subscribe (QoS 1/2)
    ├── coap_demo.c           # CoAP client/server
    ├── ota_demo.c            # Firmware update flow
    ├── filesystem_demo.c     # File I/O
    ├── watchdog_demo.c       # Watchdog configuration
    ├── low_power.c           # Power mode transitions
    ├── software_timers.c     # Timer creation and callbacks
    ├── event_groups.c        # Event synchronisation
    ├── condition_variable.c  # Producer/consumer
    ├── priority_adjustment.c # Dynamic priority
    └── task_statistics.c     # CPU and stack monitoring