# FLASH Driver Configuration | QMK Firmware
Documentation for QMK Firmware

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# FLASH Driver Configuration ​

The FLASH driver can be swapped out depending on the needs of the keyboard, or whether extra hardware is present.

Driver | Description
--- | ---
`FLASH_DRIVER = spi` | Supports writing to almost all NOR Flash chips. See the driver section below.

## SPI FLASH Driver Configuration ​

Currently QMK supports almost all NOR Flash chips over SPI. As such, requires a working spi_master driver configuration. You can override the driver configuration via your config.h:

`config.h` override | Description | Default Value
--- | --- | ---
`#define EXTERNAL_FLASH_SPI_SLAVE_SELECT_PIN` | SPI Slave select pin in order to inform that the FLASH is currently being addressed | none
`#define EXTERNAL_FLASH_SPI_CLOCK_DIVISOR` | Clock divisor used to divide the peripheral clock to derive the SPI frequency | `8`
`#define EXTERNAL_FLASH_PAGE_SIZE` | The Page size of the FLASH in bytes, as specified in the datasheet | `256`
`#define EXTERNAL_FLASH_SECTOR_SIZE` | The sector size of the FLASH in bytes, as specified in the datasheet | `(4 * 1024)`
`#define EXTERNAL_FLASH_BLOCK_SIZE` | The block size of the FLASH in bytes, as specified in the datasheet | `(64 * 1024)`
`#define EXTERNAL_FLASH_SIZE` | The total size of the FLASH in bytes, as specified in the datasheet | `(512 * 1024)`
`#define EXTERNAL_FLASH_ADDRESS_SIZE` | The Flash address size in bytes, as specified in datasheet | `3`

WARNING

All the above default configurations are based on MX25L4006E NOR Flash.