tags: - cocubes - technical - embedded-systems
Basic Embedded Systems
Definition
An embedded system is a dedicated computer inside a larger product, designed for one or a limited set of tasks. Examples: washing-machine controller, digital camera, vehicle ECU and thermostat.
Microprocessor versus microcontroller
| Microprocessor | Microcontroller |
|---|---|
| CPU usually needs external RAM, storage and peripherals | CPU, memory and I/O peripherals integrated on one chip |
| general-purpose computing | dedicated control applications |
| higher external hardware complexity | lower-cost, compact embedded design |
Core components
- CPU: executes instructions.
- Flash/ROM: non-volatile program storage.
- RAM: volatile temporary data storage.
- GPIO: general-purpose input/output pins.
- Timer/counter: measures time or counts events.
- ADC: converts analog sensor voltage to digital value.
- DAC: converts digital value to analog signal.
- PWM: simulates variable analog output using duty cycle.
- Watchdog timer: resets/reports when software hangs.
Interrupt versus polling
| Interrupt | Polling |
|---|---|
| hardware/event notifies CPU | CPU repeatedly checks device/status |
| efficient for infrequent events | simple, but can waste CPU time |
| ISR must be short and safe | response depends on polling frequency |
An interrupt service routine should save necessary state, do minimum urgent work, clear/acknowledge the event, and return quickly.
Communication interfaces
| Protocol | Wires/basic model | Main trait |
|---|---|---|
| UART | TX, RX; asynchronous | simple serial communication, no shared clock |
| SPI | clock plus data/select lines | synchronous, fast, full duplex, master-peripheral |
| I2C | SDA and SCL | two-wire addressed bus, multiple devices |
| CAN | differential bus | robust, priority-based vehicle/industrial network |
Real-time systems
Correctness depends on result and timing.
- Hard real-time: missing deadline can cause serious failure; example safety controller.
- Soft real-time: late result reduces quality but may be tolerated; example multimedia.
- RTOS: operating system designed for predictable timing/scheduling.
Embedded design answer pattern
For a sensor-controller MCQ, map:
sensor → ADC/input → microcontroller/firmware → output/actuator.
If the system may hang unattended, choose watchdog. If an urgent external event arrives, choose interrupt. If analog data must be read, choose ADC.
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