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# FLASH Driver Configuration {#flash-driver-configuration}
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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.
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## SPI FLASH Driver Configuration {#spi-flash-driver-configuration}
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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`
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::: warning
All the above default configurations are based on MX25L4006E NOR Flash.
:::
