[STM32F4] C++ Project Tutorial - Step 5

Using the SPI Peripheral in C++

The SPI (Serial Peripheral Interface) is a widely used communication interface in embedded systems for high-speed data exchange with sensors, external memory devices, displays, and more. Unlike UART, SPI follows a master/slave architecture and operates with four main signals: SCLK, MOSI, MISO, and CS (Chip Select).

In this step, we’ll explore how to design SPI communication using a class-based structure in C++. Unlike UART—where interrupt or DMA-based extensions are common—SPI protocols often vary by device, so it’s typical to derive device-specific subclasses from a shared base class, rather than creating generalized extensions.

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BaseSPI: The Core Class

The BaseSPI class provides a common foundation for SPI communication. Its key features include:

• Transmit/Receive Functions
  Supports both single-byte and multi-byte transfers.
• Communication Properties
  Manages SPI settings such as: Clock Prescaler, Clock Polarity and Phase (CPOL/CPHA), Bit Order (MSB/LSB first), Data Frame Length
• Chip Select (CS) Control
  Controls the CS pin to initiate and terminate communication with slave devices.

This class handles only general SPI operations, while device-specific command sets and protocols are implemented in derived classes.

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Device-Specific Extension Classes

Since each SPI device follows its own protocol, it’s efficient to create dedicated subclasses that inherit from BaseSPI. Examples include:

• AT25 Series EEPROMs → Require specific read/write command sets.
• External ADC/DACs → Use sampling start/stop commands and register access sequences.
• Display Controllers (e.g., ST7735, ILI9341) → Require distinguishing between command and data transmissions.

Therefore, it is most efficient to implement dedicated device-specific classes that inherit from BaseSPI.

Each device class utilizes the transfer functions of BaseSPI while implementing its own instruction set and communication protocol.

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Code Examples

Example 1 – SPI-Based EEPROM Class

1. Include Header and Declare Object

#include "BaseSPI.h"

BaseSPI tmpSPI;

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Troubleshooting & Tips

1. Corrupted data
   • Clock polarity (CPOL) or phase (CPHA) mismatch
   • Configure SPI mode (Mode 0–3) according to the device datasheet
2. No response from slave
   • CS pin not properly controlled
   • Ensure CS is driven low before and high after communication
3. Speed issues
   • Prescaler too high or too low
   • Adjust SPI clock according to device specifications
4. Protocol mismatch
   • Incorrect command/data sequence
   • Implement a dedicated device class to handle protocol details

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Conclusion

In this step, we introduced a class-based structure for implementing SPI communication:

• BaseSPI – Provides core features such as transmit/receive, CS control, and configuration management.
• Device-Specific Classes – Implement device protocols for EEPROMs, sensors, and display controllers.
• Application Layer – Simply calls the device class APIs without worrying about low-level SPI details.

In the next step, we’ll select one SPI-based device and demonstrate the actual data transfer and receive flow as a practical example.