Embedded Systems & IoT
Microcontroller Platforms
| Platform | Best For | Language | IDE |
|---|
| ESP32 | WiFi/BLE IoT devices | C/C++, MicroPython | PlatformIO, Arduino IDE |
| STM32 | Industrial, real-time | C/C++ | STM32CubeIDE, PlatformIO |
| Arduino | Prototyping, learning | C++ (Arduino) | Arduino IDE, PlatformIO |
| Raspberry Pi Pico | RP2040, dual-core | C/C++, MicroPython | Thonny, VS Code |
| nRF52 | BLE-focused IoT | C, Zephyr | nRF Connect SDK |
Firmware Patterns
GPIO & Peripherals
// ESP-IDF GPIO example
gpio_config_t io_conf = {
.pin_bit_mask = (1ULL << GPIO_NUM_2),
.mode = GPIO_MODE_OUTPUT,
.pull_up_en = GPIO_PULLUP_DISABLE,
.pull_down_en = GPIO_PULLDOWN_DISABLE,
.intr_type = GPIO_INTR_DISABLE,
};
gpio_config(&io_conf);
gpio_set_level(GPIO_NUM_2, 1);
I2C Communication
// Read sensor via I2C
i2c_cmd_handle_t cmd = i2c_cmd_link_create();
i2c_master_start(cmd);
i2c_master_write_byte(cmd, (SENSOR_ADDR << 1) | I2C_MASTER_WRITE, true);
i2c_master_write_byte(cmd, REG_TEMP, true);
i2c_master_start(cmd);
i2c_master_write_byte(cmd, (SENSOR_ADDR << 1) | I2C_MASTER_READ, true);
i2c_master_read(cmd, data, 2, I2C_MASTER_LAST_NACK);
i2c_master_stop(cmd);
i2c_master_cmd_begin(I2C_NUM_0, cmd, pdMS_TO_TICKS(1000));
i2c_cmd_link_delete(cmd);
RTOS (FreeRTOS)
// Task creation
void sensor_task(void *pvParameters) {
while (1) {
float temp = read_temperature();
xQueueSend(data_queue, &temp, portMAX_DELAY);
vTaskDelay(pdMS_TO_TICKS(1000));
}
}
xTaskCreate(sensor_task, "sensor", 4096, NULL, 5, NULL);
// Mutex for shared resources
SemaphoreHandle_t spi_mutex = xSemaphoreCreateMutex();
if (xSemaphoreTake(spi_mutex, pdMS_TO_TICKS(100)) == pdTRUE) {
spi_transfer(data);
xSemaphoreGive(spi_mutex);
}
IoT Protocols
MQTT
// ESP-IDF MQTT client
esp_mqtt_client_config_t mqtt_cfg = {
.broker.address.uri = "mqtt://broker.hivemq.com",
};
esp_mqtt_client_handle_t client = esp_mqtt_client_init(&mqtt_cfg);
esp_mqtt_client_start(client);
esp_mqtt_client_publish(client, "/sensors/temp", "23.5", 0, 1, 0);
Key IoT Protocols
| Protocol | Transport | Use Case |
|---|
| MQTT | TCP/TLS | Pub/sub messaging, telemetry |
| CoAP | UDP/DTLS | Constrained devices, REST-like |
| BLE | Radio | Short-range, low power |
| LoRaWAN | Radio | Long-range, low data rate |
| Matter | IP | Smart home interoperability |
Best Practices
- Power management: Deep sleep modes, wake-on-interrupt, duty cycling
- Watchdog timers: Always enable, reset periodically, catch firmware hangs
- OTA updates: Dual partition scheme, rollback on boot failure, signature verification
- Memory: Static allocation preferred, avoid heap fragmentation, use memory pools
- Testing: Hardware-in-the-loop (HIL), mock hardware interfaces for unit tests
