Adding QSPI Flash to STM32F4: W25Q128 Driver and Example Code

Introduction

The STM32F4CEU6 microcontroller provides 512KB of internal flash, which is sufficient for firmware but limited for data-heavy applications. When storing sensor logs, configuration files, audio data, or display assets, external flash becomes essential.

The W25Q128JV is a 16MB SPI NOR flash chip from Winbond, widely used in embedded systems due to its reliability, speed, and low cost. The NVX-F4 Flash board integrates this chip pre-wired and ready for immediate use.

This guide explains how to interface the W25Q128JV with STM32F4 using SPI, configure it in STM32CubeMX, and build a complete driver for read, write, and erase operations.

W25Q128JV Specifications

• Capacity: 128Mbit (16MB)
• Interface: SPI / Dual SPI / Quad SPI
• Max Clock: 133MHz
• Page Size: 256 bytes
• Sector Size: 4KB
• Block Size: 64KB
• Voltage: 2.7V – 3.6V
• JEDEC ID: 0xEF4018

STM32F4 SPI Flash Wiring

The NVX-F4 board already connects the flash to SPI1. For custom setups:

CubeMX Configuration

Configure SPI1 as follows:

• Mode: Full-Duplex Master
• Data Size: 8-bit
• Clock Polarity: Low
• Clock Phase: 1 Edge (SPI Mode 0)
• Baud Rate: Start around 10MHz
• GPIO: PA4 as Output (FLASH_CS)

Generate project code after configuration.

Full SPI Flash Driver

Initialization

void W25Q128_Init(SPI_HandleTypeDef *hspi) {
 _hspi = hspi;
 FLASH_CS_HIGH();
}

Read Device ID

uint32_t W25Q128_ReadID(void) {
 uint32_t id = 0;
 
 FLASH_CS_LOW();
 SPI_Transfer(0x9F);
 
 id = (uint32_t)SPI_Transfer(0xFF) << 16;
 id |= (uint32_t)SPI_Transfer(0xFF) << 8;
 id |= SPI_Transfer(0xFF);
 
 FLASH_CS_HIGH();
 return id;
}

Read Data

void W25Q128_Read(uint32_t addr, uint8_t *buf, uint16_t len) {
 FLASH_CS_LOW();
 SPI_Transfer(0x03);
 
 SPI_Transfer((addr >> 16) & 0xFF);
 SPI_Transfer((addr >> 8) & 0xFF);
 SPI_Transfer(addr & 0xFF);
 
 for (uint16_t i = 0; i < len; i++)
 buf[i] = SPI_Transfer(0xFF);
 
 FLASH_CS_HIGH();
}

Page Write

void W25Q128_WritePage(uint32_t addr, uint8_t *buf, uint16_t len) {
 FLASH_CS_LOW();
 SPI_Transfer(0x06); // Write enable
 FLASH_CS_HIGH();
 
 FLASH_CS_LOW();
 SPI_Transfer(0x02);
 
 SPI_Transfer((addr >> 16) & 0xFF);
 SPI_Transfer((addr >> 8) & 0xFF);
 SPI_Transfer(addr & 0xFF);
 
 for (uint16_t i = 0; i < len; i++)
 SPI_Transfer(buf[i]);
 
 FLASH_CS_HIGH();
 W25Q128_WaitBusy();
}

Sector Erase

void W25Q128_EraseSector(uint32_t addr) {
 FLASH_CS_LOW();
 SPI_Transfer(0x06);
 FLASH_CS_HIGH();
 
 FLASH_CS_LOW();
 SPI_Transfer(0x20);
 
 SPI_Transfer((addr >> 16) & 0xFF);
 SPI_Transfer((addr >> 8) & 0xFF);
 SPI_Transfer(addr & 0xFF);
 
 FLASH_CS_HIGH();
 W25Q128_WaitBusy();
}

Example Usage

W25Q128_Init(&hspi1);
 
uint32_t id = W25Q128_ReadID();
 
W25Q128_EraseSector(0x000000);
 
uint8_t write_buf[16] = "NVX-F4 TEST DATA";
W25Q128_WritePage(0x000000, write_buf, 16);
 
uint8_t read_buf[16] = {0};
W25Q128_Read(0x000000, read_buf, 16);

Important Notes

• Flash must be erased before writing
• Writes cannot cross 256-byte page boundaries
• Each sector supports ~100,000 erase cycles
• Always wait for BUSY flag after write/erase operations

Conclusion

The W25Q128JV makes it easy to extend STM32F4 storage far beyond internal flash limits. With SPI1 integration on the NVX-F4 board, no external wiring is required, making it ideal for data logging, firmware storage, and embedded applications.