AVR SPI Master-Slave Communication (Bare-Metal C)

Problem / Motivation

As part of my university embedded systems coursework, I developed a fully functional SPI communication protocol between two Atmega328P microcontrollers using bare-metal AVR C programming. The goal of the project was to implement real-time full-duplex data exchange at the register level without using Arduino libraries or any external abstraction layers.

This project allowed me to gain hands-on experience with synchronous serial protocols, hardware interrupt design, register configuration, and master-slave synchronization — all of which are critical for real-world embedded communication systems used in industrial, automotive, and IoT devices.

System Architecture

• Microcontrollers: Two Atmega328P boards communicating via SPI in full-duplex mode.
• Master Controller: Generates clock signals, initiates transactions, and sends command/data packets.
• Slave Controller: Fully interrupt-driven SPI slave that responds to incoming master transmissions.
• Register-Level Configuration: Direct manipulation of SPI control/status/data registers (SPCR, SPSR, SPDR) for hardware-level SPI control.
• Full-Duplex Operation: Simultaneous read/write data transfer synchronized to SPI clock.
• Interrupt Service Routines (ISRs): Efficient non-blocking communication using hardware interrupts for both master and slave data exchange.

Key Technical Challenges

• Configuring SPI control registers to correctly handle clock polarity (CPOL), clock phase (CPHA), and clock speed synchronization.
• Managing data exchange timing for full-duplex operation at hardware clock speed.
• Designing robust ISR handlers that safely handle incoming data while avoiding buffer overruns or race conditions.
• Debugging low-level SPI timing issues using logic analyzers, serial output, and oscilloscope traces.
• Writing clean modular embedded firmware that separates hardware abstraction from protocol logic.

Future Work & Expansion

• Extend protocol to handle multi-byte messages with buffering and acknowledgment.
• Implement error detection using CRC or parity checking.
• Expand to multi-slave configurations with dynamic slave addressing.
• Integrate SPI-based peripheral devices (e.g. sensors, displays) for practical embedded system applications.
• Combine with higher-layer protocol design for more complex device-to-device communication frameworks.

Technologies Used

AVR C (bare-metal), Atmega328P, SPI Protocol, Register-Level Programming, Interrupt-Driven Firmware, Real-Time Embedded Systems, Logic Analyzer Debugging

🔗 View the GitHub Repository