qmk_firmware/docs/eeprom_driver.md

EEPROM Driver Configuration :id=eeprom-driver-configuration

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

Selecting the EEPROM driver is done in your keyboard's rules.mk:

Driver	Description
EEPROM_DRIVER = vendor (default)	Uses the on-chip driver provided by the chip manufacturer. For AVR, this is provided by avr-libc. This is supported on ARM for a subset of chips -- STM32F3xx, STM32F1xx, and STM32F072xB will be emulated by writing to flash. STM32L0xx and STM32L1xx will use the onboard dedicated true EEPROM. Other chips will generally act as "transient" below.
EEPROM_DRIVER = i2c	Supports writing to I2C-based 24xx EEPROM chips. See the driver section below.
EEPROM_DRIVER = spi	Supports writing to SPI-based 25xx EEPROM chips. See the driver section below.
EEPROM_DRIVER = transient	Fake EEPROM driver -- supports reading/writing to RAM, and will be discarded when power is lost.
EEPROM_DRIVER = wear_leveling	Frontend driver for the wear_leveling system, allowing for EEPROM emulation on top of flash -- both in-MCU and external SPI NOR flash.

Vendor Driver Configuration :id=vendor-eeprom-driver-configuration

STM32 L0/L1 Configuration :id=stm32l0l1-eeprom-driver-configuration

!> Resetting EEPROM using an STM32L0/L1 device takes up to 1 second for every 1kB of internal EEPROM used.

config.h override	Description	Default Value
#define STM32_ONBOARD_EEPROM_SIZE	The size of the EEPROM to use, in bytes. Erase times can be high, so it's configurable here, if not using the default value.	Minimum required to cover base eeconfig data, or 1024 if VIA is enabled.

I2C Driver Configuration :id=i2c-eeprom-driver-configuration

Currently QMK supports 24xx-series chips over I2C. As such, requires a working i2c_master driver configuration. You can override the driver configuration via your config.h:

config.h override	Description	Default Value
#define EXTERNAL_EEPROM_I2C_BASE_ADDRESS	Base I2C address for the EEPROM -- shifted left by 1 as per i2c_master requirements	0b10100000
#define EXTERNAL_EEPROM_I2C_ADDRESS(addr)	Calculated I2C address for the EEPROM	(EXTERNAL_EEPROM_I2C_BASE_ADDRESS)
#define EXTERNAL_EEPROM_BYTE_COUNT	Total size of the EEPROM in bytes	8192
#define EXTERNAL_EEPROM_PAGE_SIZE	Page size of the EEPROM in bytes, as specified in the datasheet	32
#define EXTERNAL_EEPROM_ADDRESS_SIZE	The number of bytes to transmit for the memory location within the EEPROM	2
#define EXTERNAL_EEPROM_WRITE_TIME	Write cycle time of the EEPROM, as specified in the datasheet	5
#define EXTERNAL_EEPROM_WP_PIN	If defined the WP pin will be toggled appropriately when writing to the EEPROM.	none

Some I2C EEPROM manufacturers explicitly recommend against hardcoding the WP pin to ground. This is in order to protect the eeprom memory content during power-up/power-down/brown-out conditions at low voltage where the eeprom is still operational, but the i2c master output might be unpredictable. If a WP pin is configured, then having an external pull-up on the WP pin is recommended.

Default values and extended descriptions can be found in drivers/eeprom/eeprom_i2c.h.

Alternatively, there are pre-defined hardware configurations for available chips/modules:

Module	Equivalent #define	Source
CAT24C512 EEPROM	#define EEPROM_I2C_CAT24C512	https://www.sparkfun.com/products/14764
RM24C512C EEPROM	#define EEPROM_I2C_RM24C512C	https://www.sparkfun.com/products/14764
24LC32A EEPROM	#define EEPROM_I2C_24LC32A	https://www.microchip.com/en-us/product/24LC32A
24LC64 EEPROM	#define EEPROM_I2C_24LC64	https://www.microchip.com/en-us/product/24LC64
24LC128 EEPROM	#define EEPROM_I2C_24LC128	https://www.microchip.com/en-us/product/24LC128
24LC256 EEPROM	#define EEPROM_I2C_24LC256	https://www.sparkfun.com/products/525
MB85RC256V FRAM	#define EEPROM_I2C_MB85RC256V	https://www.adafruit.com/product/1895

?> If you find that the EEPROM is not cooperating, ensure you've correctly shifted up your EEPROM address by 1. For example, the datasheet might state the address as 0b01010000 -- the correct value of EXTERNAL_EEPROM_I2C_BASE_ADDRESS needs to be 0b10100000.

SPI Driver Configuration :id=spi-eeprom-driver-configuration

Currently QMK supports 25xx-series 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	Default Value	Description
#define EXTERNAL_EEPROM_SPI_SLAVE_SELECT_PIN	none	SPI Slave select pin in order to inform that the EEPROM is currently being addressed
#define EXTERNAL_EEPROM_SPI_CLOCK_DIVISOR	64	Clock divisor used to divide the peripheral clock to derive the SPI frequency
#define EXTERNAL_EEPROM_BYTE_COUNT	8192	Total size of the EEPROM in bytes
#define EXTERNAL_EEPROM_PAGE_SIZE	32	Page size of the EEPROM in bytes, as specified in the datasheet
#define EXTERNAL_EEPROM_ADDRESS_SIZE	2	The number of bytes to transmit for the memory location within the EEPROM

!> There's no way to determine if there is an SPI EEPROM actually responding. Generally, this will result in reads of nothing but zero.

Transient Driver configuration :id=transient-eeprom-driver-configuration

The only configurable item for the transient EEPROM driver is its size:

config.h override	Description	Default Value
#define TRANSIENT_EEPROM_SIZE	Total size of the EEPROM storage in bytes	64

Default values and extended descriptions can be found in drivers/eeprom/eeprom_transient.h.

Wear-leveling Driver Configuration :id=wear_leveling-eeprom-driver-configuration

The wear-leveling driver uses an algorithm to minimise the number of erase cycles on the underlying MCU flash memory.

There is no specific configuration for this driver, but the wear-leveling system used by this driver may need configuration. See the wear-leveling configuration section for more information.

Wear-leveling Configuration :id=wear_leveling-configuration

The wear-leveling driver has a few possible backing stores that may be used by adding to your keyboard's rules.mk file:

Driver	Description
WEAR_LEVELING_DRIVER = embedded_flash	This driver is used for emulating EEPROM by writing to embedded flash on the MCU.
WEAR_LEVELING_DRIVER = spi_flash	This driver is used to address external SPI NOR Flash peripherals.
WEAR_LEVELING_DRIVER = legacy	This driver is the "legacy" emulated EEPROM provided in historical revisions of QMK. Currently used for STM32F0xx and STM32F4x1, but slated for deprecation and removal once embedded_flash support for those MCU families is complete.

!> All wear-leveling drivers require an amount of RAM equivalent to the selected logical EEPROM size. Increasing the size to 32kB of EEPROM requires 32kB of RAM, which a significant number of MCUs simply do not have.

Wear-leveling Embedded Flash Driver Configuration :id=wear_leveling-efl-driver-configuration

This driver performs writes to the embedded flash storage embedded in the MCU. In most circumstances, the last few of sectors of flash are used in order to minimise the likelihood of collision with program code.

Configurable options in your keyboard's config.h:

config.h override	Default	Description
#define WEAR_LEVELING_EFL_FIRST_SECTOR	unset	The first sector on the MCU to use. By default this is not defined and calculated at runtime based on the MCU. However, different flash sizes on MCUs may require custom configuration.
#define WEAR_LEVELING_EFL_FLASH_SIZE	unset	Allows overriding the flash size available for use for wear-leveling. Under normal circumstances this is automatically calculated and should not need to be overridden. Specifying a size larger than the amount actually available in flash will usually prevent the MCU from booting.
#define WEAR_LEVELING_LOGICAL_SIZE	1024	Number of bytes "exposed" to the rest of QMK and denotes the size of the usable EEPROM.
#define WEAR_LEVELING_BACKING_SIZE	2048	Number of bytes used by the wear-leveling algorithm for its underlying storage, and needs to be a multiple of the logical size.
#define BACKING_STORE_WRITE_SIZE	automatic	The byte width of the underlying write used on the MCU, and is usually automatically determined from the selected MCU family. If an error occurs in the auto-detection, you'll need to consult the MCU's datasheet and determine this value, specifying it directly.

!> If your MCU does not boot after swapping to the EFL wear-leveling driver, it's likely that the flash size is incorrectly detected, usually as an MCU with larger flash and may require overriding.

Wear-leveling SPI Flash Driver Configuration :id=wear_leveling-flash_spi-driver-configuration

This driver performs writes to an external SPI NOR Flash peripheral. It also requires a working configuration for the SPI NOR Flash peripheral -- see the flash driver documentation for more information.

Configurable options in your keyboard's config.h:

config.h override	Default	Description
#define WEAR_LEVELING_EXTERNAL_FLASH_BLOCK_COUNT	1	Number of blocks in the external flash used by the wear-leveling algorithm.
#define WEAR_LEVELING_EXTERNAL_FLASH_BLOCK_OFFSET	0	The index first block in the external flash used by the wear-leveling algorithm.
#define WEAR_LEVELING_LOGICAL_SIZE	((block_count*block_size)/2)	Number of bytes "exposed" to the rest of QMK and denotes the size of the usable EEPROM. Result must be <= 64kB.
#define WEAR_LEVELING_BACKING_SIZE	(block_count*block_size)	Number of bytes used by the wear-leveling algorithm for its underlying storage, and needs to be a multiple of the logical size.
#define BACKING_STORE_WRITE_SIZE	8	The write width used whenever a write is performed on the external flash peripheral.

!> There is currently a limit of 64kB for the EEPROM subsystem within QMK, so using a larger flash is not going to be beneficial as the logical size cannot be increased beyond 65536. The backing size may be increased to a larger value, but erase timing may suffer as a result.

Wear-leveling Legacy EEPROM Emulation Driver Configuration :id=wear_leveling-legacy-driver-configuration

This driver performs writes to the embedded flash storage embedded in the MCU much like the normal Embedded Flash Driver, and is only for use with STM32F0xx and STM32F4x1 devices. This flash implementation is still currently provided as the EFL driver is currently non-functional for the previously mentioned families.

By default, 1024 bytes of emulated EEPROM is provided:

MCU	EEPROM Provided	Flash Used
STM32F042	1024 bytes	2048 bytes
STM32F070	1024 bytes	2048 bytes
STM32F072	1024 bytes	2048 bytes
STM32F401	1024 bytes	16384 bytes
STM32F411	1024 bytes	16384 bytes

Under normal circumstances configuration of this driver requires intimate knowledge of the MCU's flash structure -- reconfiguration is at your own risk and will require referring to the code.