file: spiflash.h

#ifndef __spiflash_h
#define __spiflash_h
#include "mbed.h"
class spiflash {
public:
    spiflash(SPI &Spi, DigitalOut & NSS);
    void powerUp();
    void eraseAll();
    void eraseSector(uint32_t Address);
    void enableWrite();
    void disableWrite();
    void readDataBytes(uint32_t Address, uint8_t *ByteArray, uint32_t Length);
    void writeDataBytes(uint32_t Address, uint8_t *ByteArray, uint32_t Length);
    uint32_t readDeviceIdentifier();

private:
    static const uint32_t FlashMemorySize=4194304; // Capacity of W25Q32BV
    static const uint32_t SectorSize=4096; // Erase sector size
    static const uint32_t PageSize=256; // Number of bytes that can be programmed at one time
    SPI & spi;
    DigitalOut &nSS;    
    uint32_t readStatusRegister1();
};
#endif

file: spiflash.cpp

#include "spiflash.h"
spiflash::spiflash(SPI &Spi, DigitalOut & NSS) : spi(Spi), nSS(NSS)
{
   
}
void spiflash::powerUp()
{
    char TxBuffer[4];  // Transmit buffer
    char RxBuffer[4];  // Receive buffer
    TxBuffer[0]=0xAB;  // Command 0xAB = "Release from power down"
    nSS = 0;           // Drive nCS low to connect slave to the bus
    spi.write(TxBuffer,1,RxBuffer,1); // Write 1 byte and read 1 byte
    nSS = 1;           // Drive nCS high to disconnect slave from the bus
}
void spiflash::eraseAll()
{
    enableWrite();
    // Use sparingly!!! Limited number of cycles available
    char TxBuffer[4];  // Transmit buffer
    char RxBuffer[4];  // Receive buffer
    TxBuffer[0]=0xc7;  // Command 0xc7 = "Bulk Erase"
    nSS = 0;           // Drive nCS low to connect slave to the bus
    spi.write(TxBuffer,1,RxBuffer,1); // Write 1 byte and read 1 byte
    nSS = 1;           // Drive nCS high to disconnect slave from the bus
    while (readStatusRegister1() & 1)
    { // Wait for device erase to complete       
    }
}
void spiflash::eraseSector(uint32_t Address)
{
    enableWrite();
    // Mask off the lower bits of the Sector Address (redundant?)
    //Address = Address & 0xfffc00; //0b1111 1111 1111 1100 0000 0000
    // Use sparingly!!! Limited number of cycles available
    char TxBuffer[4];  // Transmit buffer
    char RxBuffer[4];  // Receive buffer
    
    TxBuffer[0]=0x20;  // Command 0x20 = "Sector Erase"
    TxBuffer[1] = (Address >> 16) & 0xff;
    TxBuffer[2] = (Address >> 8) & 0xff;
    TxBuffer[3] = (Address & 0xff);
    nSS = 0;           // Drive nCS low to connect slave to the bus
    spi.write(TxBuffer,4,RxBuffer,1); // Write 1 byte and read 1 byte
    nSS = 1;           // Drive nCS high to disconnect slave from the bus
    while (readStatusRegister1() & 1)
    {
        // Wait for sector erase to complete
    }
}
void spiflash::enableWrite()
{
    char TxBuffer[4];  // Transmit buffer
    char RxBuffer[4];  // Receive buffer
    TxBuffer[0]=0x06;  // Command 0x06 = "Enable writes"
    nSS = 0;           // Drive nCS low to connect slave to the bus
    spi.write(TxBuffer,1,RxBuffer,1); // Write 1 byte and read 1 byte
    nSS = 1;           // Drive nSS high to disconnect slave from the bus
}
void spiflash::disableWrite()
{
    char TxBuffer[4];  // Transmit buffer
    char RxBuffer[4];  // Receive buffer
    TxBuffer[0]=0x06;  // Command 0x06 = "Disable writes"
    nSS = 0;           // Drive nCS low to connect slave to the bus
    spi.write(TxBuffer,1,RxBuffer,1); // Write 1 byte and read 1 byte
    nSS = 1;           // Drive nSS high to disconnect slave from the bus
}
void spiflash::readDataBytes(uint32_t Address, uint8_t *ByteArray, uint32_t Length)
{    
    // Read Length bytes starting at Address and return in ByteArray
    char TxBuffer[4];   // Transmit buffer
    TxBuffer[0]=0x03;   // Command 0x03 = "Read bytes"
    nSS = 0;
    TxBuffer[1] = (Address >> 16) & 0xff;
    TxBuffer[2] = (Address >> 8) & 0xff;
    TxBuffer[3] = (Address) & 0xff;
    spi.write(TxBuffer,4,0,0); // Send command and Address of interest
    spi.write(0,0,(char *)ByteArray,Length); // Send command and Address of interest
    nSS = 1;
}
void spiflash::writeDataBytes(uint32_t Address, uint8_t *ByteArray, uint32_t Length)
{
    enableWrite();
    char TxBuffer[4];   // Transmit buffer
    
    TxBuffer[0]=0x02;   // Command 0x02 = "Write bytes"
    TxBuffer[1] = (Address >> 16) & 0xff;
    TxBuffer[2] = (Address >> 8) & 0xff;
    TxBuffer[3] = (Address) & 0xff;
    nSS = 0;
    spi.write(TxBuffer,4,0,0); // Send command and Address of interest
    spi.write((char *)ByteArray, Length, 0,0); // Send command and Address of interest
    nSS = 1;
    while (readStatusRegister1() & 1)
    {
        // Wait for write data to complete
    }
}
uint32_t spiflash::readDeviceIdentifier()
{
    // If the chip conforms with JEDEC norms, the last byte of the ID should 
    // indicate the capacity.  The last byte is the size of the chip express
    // in powers of 2.  For example if you read 0x16 (22 decimal) then the
    // chip should have a capacity of 2^22 = 4MiB.
    char TxBuffer[4];  // Transmit buffer
    char RxBuffer[4];  // Receive buffer
    TxBuffer[0]=0x9f;  // Command 0x9f = "Read status Device ID"
    nSS = 0;           // Drive nCS low to connect slave to the bus
    spi.write(TxBuffer,1,RxBuffer,4); // Write 1 byte and read 4 bytes
    nSS = 1;           // Drive nCS high to disconnect slave from the bus
    uint32_t ID=RxBuffer[1];
    ID = ID << 8;
    ID += RxBuffer[2];
    ID = ID << 8;
    ID += RxBuffer[3];
    return ID; // return the status register contents     
}
uint32_t spiflash::readStatusRegister1()
{
    char TxBuffer[4];  // Transmit buffer
    char RxBuffer[4];  // Receive buffer
    TxBuffer[0]=0x05;  // Command 0x9f = "Read Status register 1"
    nSS = 0;           // Drive nCS low to connect slave to the bus
    spi.write(TxBuffer,1,RxBuffer,2); // Write 1 byte and read 1 byte
    nSS = 1;           // Drive nCS high to disconnect slave from the bus
    return RxBuffer[1]; // return the status register contents 
    
}