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opensteno_qmk/docs/eeprom_driver.md
Nick Brassel f2f2afe13b
Add support for STM32L0/L1 onboard EEPROM. (#8002) 
* Add support for STM32L0/L1 onboard EEPROM.

* Update docs/eeprom_driver.md

Co-Authored-By: Joel Challis <git@zvecr.com>

Co-authored-by: Joel Challis <git@zvecr.com>
2020-03-12 12:59:55 +11:00

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EEPROM Driver Configuration

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

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 = transient Fake EEPROM driver -- supports reading/writing to RAM, and will be discarded when power is lost.

Vendor Driver Configuration

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

No configurable options are available.

I2C 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

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
24LC128 EEPROM #define EEPROM_I2C_24LC128 https://www.microchip.com/wwwproducts/en/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.

Transient 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.