Add customisable EEPROM driver selection (#7274)

- uprintf -> dprintf
- Fix atsam "vendor" eeprom.
- Bump Kinetis K20x to 64 bytes, too.
- Rollback Kinetis to 32 bytes as partitioning can only be done once. Add warning about changing the value.
- Change RAM-backed "fake" EEPROM implementations to match eeconfig's current usage.
- Add 24LC128 by request.

20 files changed, 616 insertions, 52 deletions

diff --git a/common_features.mk b/common_features.mk
index 6c3646db9..900b27c46 100644
--- a/common_features.mk
+++ b/common_features.mk
@@ -102,6 +102,57 @@ ifeq ($(strip $(UNICODE_COMMON)), yes)
     SRC += $(QUANTUM_DIR)/process_keycode/process_unicode_common.c
 endif
 
+VALID_EEPROM_DRIVER_TYPES := vendor custom transient i2c
+EEPROM_DRIVER ?= vendor
+ifeq ($(filter $(EEPROM_DRIVER),$(VALID_EEPROM_DRIVER_TYPES)),)
+  $(error EEPROM_DRIVER="$(EEPROM_DRIVER)" is not a valid EEPROM driver)
+else
+  OPT_DEFS += -DEEPROM_ENABLE
+  ifeq ($(strip $(EEPROM_DRIVER)), custom)
+    OPT_DEFS += -DEEPROM_DRIVER -DEEPROM_CUSTOM
+    COMMON_VPATH += $(DRIVER_PATH)/eeprom
+    SRC += eeprom_driver.c
+  else ifeq ($(strip $(EEPROM_DRIVER)), i2c)
+    OPT_DEFS += -DEEPROM_DRIVER -DEEPROM_I2C
+    COMMON_VPATH += $(DRIVER_PATH)/eeprom
+    QUANTUM_LIB_SRC += i2c_master.c
+    SRC += eeprom_driver.c eeprom_i2c.c
+  else ifeq ($(strip $(EEPROM_DRIVER)), transient)
+    OPT_DEFS += -DEEPROM_DRIVER -DEEPROM_TRANSIENT
+    COMMON_VPATH += $(DRIVER_PATH)/eeprom
+    SRC += eeprom_driver.c eeprom_transient.c
+  else ifeq ($(strip $(EEPROM_DRIVER)), vendor)
+    OPT_DEFS += -DEEPROM_VENDOR
+    ifeq ($(PLATFORM),AVR)
+      # Automatically provided by avr-libc, nothing required
+    else ifeq ($(PLATFORM),CHIBIOS)
+      ifeq ($(MCU_SERIES), STM32F3xx)
+        SRC += $(PLATFORM_COMMON_DIR)/eeprom_stm32.c
+        SRC += $(PLATFORM_COMMON_DIR)/flash_stm32.c
+        OPT_DEFS += -DEEPROM_EMU_STM32F303xC
+        OPT_DEFS += -DSTM32_EEPROM_ENABLE
+      else ifeq ($(MCU_SERIES), STM32F1xx)
+        SRC += $(PLATFORM_COMMON_DIR)/eeprom_stm32.c
+        SRC += $(PLATFORM_COMMON_DIR)/flash_stm32.c
+        OPT_DEFS += -DEEPROM_EMU_STM32F103xB
+        OPT_DEFS += -DSTM32_EEPROM_ENABLE
+      else ifeq ($(MCU_SERIES)_$(MCU_LDSCRIPT), STM32F0xx_STM32F072xB)
+        SRC += $(PLATFORM_COMMON_DIR)/eeprom_stm32.c
+        SRC += $(PLATFORM_COMMON_DIR)/flash_stm32.c
+        OPT_DEFS += -DEEPROM_EMU_STM32F072xB
+        OPT_DEFS += -DSTM32_EEPROM_ENABLE
+      else
+        # This will effectively work the same as "transient" if not supported by the chip
+        SRC += $(PLATFORM_COMMON_DIR)/eeprom_teensy.c
+      endif
+    else ifeq ($(PLATFORM),ARM_ATSAM)
+      SRC += $(PLATFORM_COMMON_DIR)/eeprom.c
+    else ifeq ($(PLATFORM),TEST)
+      SRC += $(PLATFORM_COMMON_DIR)/eeprom.c
+    endif
+  endif
+endif
+
 ifeq ($(strip $(RGBLIGHT_ENABLE)), yes)
     POST_CONFIG_H += $(QUANTUM_DIR)/rgblight_post_config.h
     OPT_DEFS += -DRGBLIGHT_ENABLE
diff --git a/docs/_summary.md b/docs/_summary.md
index de8148138..08ccdca22 100644
--- a/docs/_summary.md
+++ b/docs/_summary.md
@@ -104,6 +104,7 @@
   * [ADC Driver](adc_driver.md)
   * [I2C Driver](i2c_driver.md)
   * [WS2812 Driver](ws2812_driver.md)
+  * [EEPROM Driver](eeprom_driver.md)
   * [GPIO Controls](internals_gpio_control.md)
   * [Custom Matrix](custom_matrix.md)
   * [Proton C Conversion](proton_c_conversion.md)
diff --git a/docs/eeprom_driver.md b/docs/eeprom_driver.md
new file mode 100644
index 000000000..dd12d8ec7
--- /dev/null
+++ b/docs/eeprom_driver.md
@@ -0,0 +1,50 @@
+# 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`    | 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. 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
+
+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`.
diff --git a/docs/hardware_drivers.md b/docs/hardware_drivers.md
index 165187795..7e89c0d2b 100644
--- a/docs/hardware_drivers.md
+++ b/docs/hardware_drivers.md
@@ -33,3 +33,7 @@ Support for up to 2 drivers. Each driver impliments 2 charlieplex matrices to in
 ## IS31FL3733
 
 Support for up to a single driver with room for expansion. Each driver can control 192 individual LEDs or 64 RGB LEDs. For more information on how to setup the driver see the [RGB Matrix](feature_rgb_matrix.md) page.
+
+## 24xx series external I2C EEPROM
+
+Support for an external I2C-based EEPROM instead of using the on-chip EEPROM. For more information on how to setup the driver see the [EEPROM Driver](eeprom_driver.md) page.
diff --git a/drivers/eeprom/eeprom_custom.c-template b/drivers/eeprom/eeprom_custom.c-template
new file mode 100644
index 000000000..5f915f7fa
--- /dev/null
+++ b/drivers/eeprom/eeprom_custom.c-template
@@ -0,0 +1,46 @@
+/* Copyright 2019 Nick Brassel (tzarc)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdint.h>
+#include <string.h>
+
+#include "eeprom_driver.h"
+
+void eeprom_driver_init(void) {
+    /* Any initialisation code */
+ }
+
+void eeprom_driver_erase(void) {
+    /* Wipe out the EEPROM, setting values to zero */
+}
+
+void eeprom_read_block(void *buf, const void *addr, size_t len) {
+    /*
+        Read a block of data:
+            buf: target buffer
+            addr: 0-based offset within the EEPROM
+            len: length to read
+     */
+}
+
+void eeprom_write_block(const void *buf, void *addr, size_t len) {
+    /*
+        Write a block of data:
+            buf: target buffer
+            addr: 0-based offset within the EEPROM
+            len: length to write
+     */
+}
diff --git a/drivers/eeprom/eeprom_driver.c b/drivers/eeprom/eeprom_driver.c
new file mode 100644
index 000000000..3835e5e9d
--- /dev/null
+++ b/drivers/eeprom/eeprom_driver.c
@@ -0,0 +1,73 @@
+/* Copyright 2019 Nick Brassel (tzarc)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdint.h>
+#include <string.h>
+
+#include "eeprom_driver.h"
+
+uint8_t eeprom_read_byte(const uint8_t *addr) {
+    uint8_t ret;
+    eeprom_read_block(&ret, addr, 1);
+    return ret;
+}
+
+uint16_t eeprom_read_word(const uint16_t *addr) {
+    uint16_t ret;
+    eeprom_read_block(&ret, addr, 2);
+    return ret;
+}
+
+uint32_t eeprom_read_dword(const uint32_t *addr) {
+    uint32_t ret;
+    eeprom_read_block(&ret, addr, 4);
+    return ret;
+}
+
+void eeprom_write_byte(uint8_t *addr, uint8_t value) { eeprom_write_block(&value, addr, 1); }
+
+void eeprom_write_word(uint16_t *addr, uint16_t value) { eeprom_write_block(&value, addr, 2); }
+
+void eeprom_write_dword(uint32_t *addr, uint32_t value) { eeprom_write_block(&value, addr, 4); }
+
+void eeprom_update_block(const void *buf, void *addr, size_t len) {
+    uint8_t read_buf[len];
+    eeprom_read_block(read_buf, addr, len);
+    if (memcmp(buf, read_buf, len) != 0) {
+        eeprom_write_block(buf, addr, len);
+    }
+}
+
+void eeprom_update_byte(uint8_t *addr, uint8_t value) {
+    uint8_t orig = eeprom_read_byte(addr);
+    if (orig != value) {
+        eeprom_write_byte(addr, value);
+    }
+}
+
+void eeprom_update_word(uint16_t *addr, uint16_t value) {
+    uint16_t orig = eeprom_read_word(addr);
+    if (orig != value) {
+        eeprom_write_word(addr, value);
+    }
+}
+
+void eeprom_update_dword(uint32_t *addr, uint32_t value) {
+    uint32_t orig = eeprom_read_dword(addr);
+    if (orig != value) {
+        eeprom_write_dword(addr, value);
+    }
+}
diff --git a/drivers/eeprom/eeprom_driver.h b/drivers/eeprom/eeprom_driver.h
new file mode 100644
index 000000000..74592bc8f
--- /dev/null
+++ b/drivers/eeprom/eeprom_driver.h
@@ -0,0 +1,22 @@
+/* Copyright 2019 Nick Brassel (tzarc)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include "eeprom.h"
+
+void eeprom_driver_init(void);
+void eeprom_driver_erase(void);
diff --git a/drivers/eeprom/eeprom_i2c.c b/drivers/eeprom/eeprom_i2c.c
new file mode 100644
index 000000000..03dbc5e51
--- /dev/null
+++ b/drivers/eeprom/eeprom_i2c.c
@@ -0,0 +1,120 @@
+/* Copyright 2019 Nick Brassel (tzarc)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdint.h>
+#include <string.h>
+
+/*
+    Note that the implementations of eeprom_XXXX_YYYY on AVR are normally
+    provided by avr-libc. The same functions are reimplemented below and are
+    rerouted to the external i2c equivalent.
+
+    Seemingly, as this is compiled from within QMK, the object file generated
+    during the build overrides the avr-libc implementation during the linking
+    stage.
+
+    On other platforms such as ARM, there are no provided implementations, so
+    there is nothing to override during linkage.
+*/
+
+#include "wait.h"
+#include "i2c_master.h"
+#include "eeprom.h"
+#include "eeprom_i2c.h"
+
+// #define DEBUG_EEPROM_OUTPUT
+
+#ifdef DEBUG_EEPROM_OUTPUT
+#    include "print.h"
+#endif  // DEBUG_EEPROM_OUTPUT
+
+static inline void init_i2c_if_required(void) {
+    static int done = 0;
+    if (!done) {
+        i2c_init();
+        done = 1;
+    }
+}
+
+static inline void fill_target_address(uint8_t *buffer, const void *addr) {
+    intptr_t p = (intptr_t)addr;
+    for (int i = 0; i < EXTERNAL_EEPROM_ADDRESS_SIZE; ++i) {
+        buffer[EXTERNAL_EEPROM_ADDRESS_SIZE - 1 - i] = p & 0xFF;
+        p >>= 8;
+    }
+}
+
+void eeprom_driver_init(void) {}
+
+void eeprom_driver_erase(void) {
+    uint8_t buf[EXTERNAL_EEPROM_PAGE_SIZE];
+    memset(buf, 0x00, EXTERNAL_EEPROM_PAGE_SIZE);
+    for (intptr_t addr = 0; addr < EXTERNAL_EEPROM_BYTE_COUNT; addr += EXTERNAL_EEPROM_PAGE_SIZE) {
+        eeprom_write_block(buf, (void *)addr, EXTERNAL_EEPROM_PAGE_SIZE);
+    }
+}
+
+void eeprom_read_block(void *buf, const void *addr, size_t len) {
+    uint8_t complete_packet[EXTERNAL_EEPROM_ADDRESS_SIZE];
+    fill_target_address(complete_packet, addr);
+
+    init_i2c_if_required();
+    i2c_transmit(EXTERNAL_EEPROM_I2C_ADDRESS((intptr_t)addr), complete_packet, EXTERNAL_EEPROM_ADDRESS_SIZE, 100);
+    i2c_receive(EXTERNAL_EEPROM_I2C_ADDRESS((intptr_t)addr), buf, len, 100);
+
+#ifdef DEBUG_EEPROM_OUTPUT
+    dprintf("[EEPROM R] 0x%04X: ", ((int)addr));
+    for (size_t i = 0; i < len; ++i) {
+        dprintf(" %02X", (int)(((uint8_t *)buf)[i]));
+    }
+    dprintf("\n");
+#endif  // DEBUG_EEPROM_OUTPUT
+}
+
+void eeprom_write_block(const void *buf, void *addr, size_t len) {
+    uint8_t  complete_packet[EXTERNAL_EEPROM_ADDRESS_SIZE + EXTERNAL_EEPROM_PAGE_SIZE];
+    uint8_t *read_buf    = (uint8_t *)buf;
+    intptr_t target_addr = (intptr_t)addr;
+
+    init_i2c_if_required();
+    while (len > 0) {
+        intptr_t page_offset  = target_addr % EXTERNAL_EEPROM_PAGE_SIZE;
+        int      write_length = EXTERNAL_EEPROM_PAGE_SIZE - page_offset;
+        if (write_length > len) {
+            write_length = len;
+        }
+
+        fill_target_address(complete_packet, (const void *)target_addr);
+        for (uint8_t i = 0; i < write_length; i++) {
+            complete_packet[EXTERNAL_EEPROM_ADDRESS_SIZE + i] = read_buf[i];
+        }
+
+#ifdef DEBUG_EEPROM_OUTPUT
+        dprintf("[EEPROM W] 0x%04X: ", ((int)target_addr));
+        for (uint8_t i = 0; i < write_length; i++) {
+            dprintf(" %02X", (int)(read_buf[i]));
+        }
+        dprintf("\n");
+#endif  // DEBUG_EEPROM_OUTPUT
+
+        i2c_transmit(EXTERNAL_EEPROM_I2C_ADDRESS((intptr_t)addr), complete_packet, EXTERNAL_EEPROM_ADDRESS_SIZE + write_length, 100);
+        wait_ms(EXTERNAL_EEPROM_WRITE_TIME);
+
+        read_buf += write_length;
+        target_addr += write_length;
+        len -= write_length;
+    }
+}
diff --git a/drivers/eeprom/eeprom_i2c.h b/drivers/eeprom/eeprom_i2c.h
new file mode 100644
index 000000000..51bce825b
--- /dev/null
+++ b/drivers/eeprom/eeprom_i2c.h
@@ -0,0 +1,115 @@
+/* Copyright 2019 Nick Brassel (tzarc)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+/*
+    Default device configurations:
+
+    For the Sparkfun Qwiic I2C EEPROM module: https://www.sparkfun.com/products/14764
+        #define EEPROM_I2C_CAT24C512 // (part number 24512A)
+        #define EEPROM_I2C_RM24C512C // (part number 24512C)
+
+    For the Sparkfun I2C EEPROM chip: https://www.sparkfun.com/products/525
+        #define EEPROM_I2C_24LC256
+
+    For the Adafruit I2C FRAM chip: https://www.adafruit.com/product/1895
+        #define EEPROM_I2C_MB85RC256V
+*/
+#if defined(EEPROM_I2C_CAT24C512)
+#    define EXTERNAL_EEPROM_BYTE_COUNT 65536
+#    define EXTERNAL_EEPROM_PAGE_SIZE 128
+#    define EXTERNAL_EEPROM_ADDRESS_SIZE 2
+#    define EXTERNAL_EEPROM_WRITE_TIME 5
+#elif defined(EEPROM_I2C_RM24C512C)
+#    define EXTERNAL_EEPROM_BYTE_COUNT 65536
+#    define EXTERNAL_EEPROM_PAGE_SIZE 128
+#    define EXTERNAL_EEPROM_ADDRESS_SIZE 2
+#    define EXTERNAL_EEPROM_WRITE_TIME 3
+#elif defined(EEPROM_I2C_24LC256)
+#    define EXTERNAL_EEPROM_BYTE_COUNT 32768
+#    define EXTERNAL_EEPROM_PAGE_SIZE 64
+#    define EXTERNAL_EEPROM_ADDRESS_SIZE 2
+#    define EXTERNAL_EEPROM_WRITE_TIME 5
+#elif defined(EEPROM_I2C_24LC128)
+#    define EXTERNAL_EEPROM_BYTE_COUNT 16384
+#    define EXTERNAL_EEPROM_PAGE_SIZE 64
+#    define EXTERNAL_EEPROM_ADDRESS_SIZE 2
+#    define EXTERNAL_EEPROM_WRITE_TIME 5
+#elif defined(EEPROM_I2C_MB85RC256V)
+#    define EXTERNAL_EEPROM_BYTE_COUNT 32768
+#    define EXTERNAL_EEPROM_PAGE_SIZE 128
+#    define EXTERNAL_EEPROM_ADDRESS_SIZE 2
+#    define EXTERNAL_EEPROM_WRITE_TIME 0
+#endif
+
+/*
+    The base I2C address of the EEPROM.
+    This needs to be shifted up by 1, to match i2c_master requirements.
+*/
+#ifndef EXTERNAL_EEPROM_I2C_BASE_ADDRESS
+#    define EXTERNAL_EEPROM_I2C_BASE_ADDRESS 0b10100000
+#endif
+
+/*
+    The calculated I2C address based on the input memory location.
+
+    For EEPROM chips that embed part of the memory location in the I2C address
+    such as AT24M02 you can use something similar to the following (ensuring the
+    result is shifted by left by 1):
+
+    #define EXTERNAL_EEPROM_I2C_ADDRESS(loc) \
+        (EXTERNAL_EEPROM_I2C_BASE_ADDRESS | ((((loc) >> 16) & 0x07) << 1))
+
+*/
+#ifndef EXTERNAL_EEPROM_I2C_ADDRESS
+#    define EXTERNAL_EEPROM_I2C_ADDRESS(loc) (EXTERNAL_EEPROM_I2C_BASE_ADDRESS)
+#endif
+
+/*
+    The total size of the EEPROM, in bytes. The EEPROM datasheet will usually
+    specify this value in kbits, and will require conversion to bytes.
+*/
+#ifndef EXTERNAL_EEPROM_BYTE_COUNT
+#    define EXTERNAL_EEPROM_BYTE_COUNT 8192
+#endif
+
+/*
+    The page size in bytes of the EEPROM, as specified in the datasheet.
+*/
+#ifndef EXTERNAL_EEPROM_PAGE_SIZE
+#    define EXTERNAL_EEPROM_PAGE_SIZE 32
+#endif
+
+/*
+    The address size in bytes of the EEPROM. For EEPROMs with <=256 bytes, this
+    will likely be 1. For EEPROMs >256 and <=65536, this will be 2. For EEPROMs
+    >65536, this will likely need to be 2 with the modified variant of
+    EXTERNAL_EEPROM_I2C_ADDRESS above.
+
+    As expected, consult the datasheet for specifics of your EEPROM.
+*/
+#ifndef EXTERNAL_EEPROM_ADDRESS_SIZE
+#    define EXTERNAL_EEPROM_ADDRESS_SIZE 2
+#endif
+
+/*
+    The write cycle time of the EEPROM in milliseconds, as specified in the
+    datasheet.
+*/
+#ifndef EXTERNAL_EEPROM_WRITE_TIME
+#    define EXTERNAL_EEPROM_WRITE_TIME 5
+#endif
diff --git a/drivers/eeprom/eeprom_transient.c b/drivers/eeprom/eeprom_transient.c
new file mode 100644
index 000000000..b4c78c6f4
--- /dev/null
+++ b/drivers/eeprom/eeprom_transient.c
@@ -0,0 +1,52 @@
+/* Copyright 2019 Nick Brassel (tzarc)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdint.h>
+#include <string.h>
+
+#include "eeprom_driver.h"
+#include "eeprom_transient.h"
+
+__attribute__((aligned(4))) static uint8_t transientBuffer[TRANSIENT_EEPROM_SIZE] = {0};
+
+size_t clamp_length(intptr_t offset, size_t len) {
+    if (offset + len > TRANSIENT_EEPROM_SIZE) {
+        len = TRANSIENT_EEPROM_SIZE - offset;
+    }
+
+    return len;
+}
+
+void eeprom_driver_init(void) { eeprom_driver_erase(); }
+
+void eeprom_driver_erase(void) { memset(transientBuffer, 0x00, TRANSIENT_EEPROM_SIZE); }
+
+void eeprom_read_block(void *buf, const void *addr, size_t len) {
+    intptr_t offset = (intptr_t)addr;
+    memset(buf, 0x00, len);
+    len = clamp_length(offset, len);
+    if (len > 0) {
+        memcpy(buf, &transientBuffer[offset], len);
+    }
+}
+
+void eeprom_write_block(const void *buf, void *addr, size_t len) {
+    intptr_t offset = (intptr_t)addr;
+    len             = clamp_length(offset, len);
+    if (len > 0) {
+        memcpy(&transientBuffer[offset], buf, len);
+    }
+}
diff --git a/drivers/eeprom/eeprom_transient.h b/drivers/eeprom/eeprom_transient.h
new file mode 100644
index 000000000..ca9d634f0
--- /dev/null
+++ b/drivers/eeprom/eeprom_transient.h
@@ -0,0 +1,25 @@
+/* Copyright 2019 Nick Brassel (tzarc)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+/*
+    The size of the transient EEPROM buffer size.
+*/
+#ifndef TRANSIENT_EEPROM_SIZE
+#    include "eeconfig.h"
+#    define TRANSIENT_EEPROM_SIZE (((EECONFIG_SIZE+3)/4)*4)  // based off eeconfig's current usage, aligned to 4-byte sizes, to deal with LTO
+#endif
diff --git a/quantum/audio/audio_arm.c b/quantum/audio/audio_arm.c
index 87d625301..e4483c302 100644
--- a/quantum/audio/audio_arm.c
+++ b/quantum/audio/audio_arm.c
@@ -258,7 +258,7 @@ void audio_init() {
     }
 
 // Check EEPROM
-#if defined(STM32_EEPROM_ENABLE) || defined(PROTOCOL_ARM_ATSAM) || defined(EEPROM_SIZE)
+#ifdef EEPROM_ENABLE
     if (!eeconfig_is_enabled()) {
         eeconfig_init();
     }
diff --git a/quantum/rgblight.c b/quantum/rgblight.c
index 40de19eac..67d601af7 100644
--- a/quantum/rgblight.c
+++ b/quantum/rgblight.c
@@ -19,9 +19,11 @@
 #    include <avr/eeprom.h>
 #    include <avr/interrupt.h>
 #endif
+#ifdef EEPROM_ENABLE
+#    include "eeprom.h"
+#endif
 #ifdef STM32_EEPROM_ENABLE
 #    include "hal.h"
-#    include "eeprom.h"
 #    include "eeprom_stm32.h"
 #endif
 #include "wait.h"
@@ -146,7 +148,7 @@ void rgblight_check_config(void) {
 }
 
 uint32_t eeconfig_read_rgblight(void) {
-#if defined(__AVR__) || defined(STM32_EEPROM_ENABLE) || defined(PROTOCOL_ARM_ATSAM) || defined(EEPROM_SIZE)
+#ifdef EEPROM_ENABLE
     return eeprom_read_dword(EECONFIG_RGBLIGHT);
 #else
     return 0;
@@ -154,7 +156,7 @@ uint32_t eeconfig_read_rgblight(void) {
 }
 
 void eeconfig_update_rgblight(uint32_t val) {
-#if defined(__AVR__) || defined(STM32_EEPROM_ENABLE) || defined(PROTOCOL_ARM_ATSAM) || defined(EEPROM_SIZE)
+#ifdef EEPROM_ENABLE
     rgblight_check_config();
     eeprom_update_dword(EECONFIG_RGBLIGHT, val);
 #endif
diff --git a/tmk_core/common.mk b/tmk_core/common.mk
index 8f355da12..5f149d8f4 100644
--- a/tmk_core/common.mk
+++ b/tmk_core/common.mk
@@ -26,29 +26,11 @@ TMK_COMMON_SRC +=	$(COMMON_DIR)/host.c \
         $(PLATFORM_COMMON_DIR)/bootloader.c \
 
 ifeq ($(PLATFORM),AVR)
-        TMK_COMMON_SRC += $(PLATFORM_COMMON_DIR)/xprintf.S
+  TMK_COMMON_SRC += $(PLATFORM_COMMON_DIR)/xprintf.S
 endif
 
 ifeq ($(PLATFORM),CHIBIOS)
-        TMK_COMMON_SRC += $(PLATFORM_COMMON_DIR)/printf.c
-  ifeq ($(MCU_SERIES), STM32F3xx)
-    TMK_COMMON_SRC += $(PLATFORM_COMMON_DIR)/eeprom_stm32.c
-    TMK_COMMON_SRC += $(PLATFORM_COMMON_DIR)/flash_stm32.c
-    TMK_COMMON_DEFS += -DEEPROM_EMU_STM32F303xC
-    TMK_COMMON_DEFS += -DSTM32_EEPROM_ENABLE
-  else ifeq ($(MCU_SERIES), STM32F1xx)
-    TMK_COMMON_SRC += $(PLATFORM_COMMON_DIR)/eeprom_stm32.c
-    TMK_COMMON_SRC += $(PLATFORM_COMMON_DIR)/flash_stm32.c
-    TMK_COMMON_DEFS += -DEEPROM_EMU_STM32F103xB
-    TMK_COMMON_DEFS += -DSTM32_EEPROM_ENABLE
-  else ifeq ($(MCU_SERIES)_$(MCU_LDSCRIPT), STM32F0xx_STM32F072xB)
-    TMK_COMMON_SRC += $(PLATFORM_COMMON_DIR)/eeprom_stm32.c
-    TMK_COMMON_SRC += $(PLATFORM_COMMON_DIR)/flash_stm32.c
-    TMK_COMMON_DEFS += -DEEPROM_EMU_STM32F072xB
-    TMK_COMMON_DEFS += -DSTM32_EEPROM_ENABLE
-  else
-    TMK_COMMON_SRC += $(PLATFORM_COMMON_DIR)/eeprom_teensy.c
-  endif
+  TMK_COMMON_SRC += $(PLATFORM_COMMON_DIR)/printf.c
   ifeq ($(strip $(AUTO_SHIFT_ENABLE)), yes)
     TMK_COMMON_SRC += $(CHIBIOS)/os/various/syscalls.c
   else ifeq ($(strip $(TERMINAL_ENABLE)), yes)
@@ -57,15 +39,9 @@ ifeq ($(PLATFORM),CHIBIOS)
 endif
 
 ifeq ($(PLATFORM),ARM_ATSAM)
-        TMK_COMMON_SRC += $(PLATFORM_COMMON_DIR)/printf.c
-        TMK_COMMON_SRC += $(PLATFORM_COMMON_DIR)/eeprom.c
+  TMK_COMMON_SRC += $(PLATFORM_COMMON_DIR)/printf.c
 endif
 
-ifeq ($(PLATFORM),TEST)
-        TMK_COMMON_SRC += $(PLATFORM_COMMON_DIR)/eeprom.c
-endif
-
-
 
 # Option modules
 BOOTMAGIC_ENABLE ?= no
diff --git a/tmk_core/common/arm_atsam/eeprom.c b/tmk_core/common/arm_atsam/eeprom.c
index 44a0bf4d7..a69f38282 100644
--- a/tmk_core/common/arm_atsam/eeprom.c
+++ b/tmk_core/common/arm_atsam/eeprom.c
@@ -16,9 +16,12 @@
 
 #include "eeprom.h"
 
-#define EEPROM_SIZE 32
+#ifndef EEPROM_SIZE
+#    include "eeconfig.h"
+#    define EEPROM_SIZE (((EECONFIG_SIZE+3)/4)*4)  // based off eeconfig's current usage, aligned to 4-byte sizes, to deal with LTO
+#endif
 
-static uint8_t buffer[EEPROM_SIZE];
+__attribute__((aligned(4))) static uint8_t buffer[EEPROM_SIZE];
 
 uint8_t eeprom_read_byte(const uint8_t *addr) {
     uintptr_t offset = (uintptr_t)addr;
@@ -40,7 +43,7 @@ uint32_t eeprom_read_dword(const uint32_t *addr) {
     return eeprom_read_byte(p) | (eeprom_read_byte(p + 1) << 8) | (eeprom_read_byte(p + 2) << 16) | (eeprom_read_byte(p + 3) << 24);
 }
 
-void eeprom_read_block(void *buf, const void *addr, uint32_t len) {
+void eeprom_read_block(void *buf, const void *addr, size_t len) {
     const uint8_t *p    = (const uint8_t *)addr;
     uint8_t *      dest = (uint8_t *)buf;
     while (len--) {
@@ -62,7 +65,7 @@ void eeprom_write_dword(uint32_t *addr, uint32_t value) {
     eeprom_write_byte(p, value >> 24);
 }
 
-void eeprom_write_block(const void *buf, void *addr, uint32_t len) {
+void eeprom_write_block(const void *buf, void *addr, size_t len) {
     uint8_t *      p   = (uint8_t *)addr;
     const uint8_t *src = (const uint8_t *)buf;
     while (len--) {
@@ -86,7 +89,7 @@ void eeprom_update_dword(uint32_t *addr, uint32_t value) {
     eeprom_write_byte(p, value >> 24);
 }
 
-void eeprom_update_block(const void *buf, void *addr, uint32_t len) {
+void eeprom_update_block(const void *buf, void *addr, size_t len) {
     uint8_t *      p   = (uint8_t *)addr;
     const uint8_t *src = (const uint8_t *)buf;
     while (len--) {
diff --git a/tmk_core/common/chibios/eeprom_stm32.c b/tmk_core/common/chibios/eeprom_stm32.c
index 926b581c6..ea5198972 100644
--- a/tmk_core/common/chibios/eeprom_stm32.c
+++ b/tmk_core/common/chibios/eeprom_stm32.c
@@ -173,7 +173,7 @@ void eeprom_update_dword(uint32_t *Address, uint32_t Value) {
     }
 }
 
-void eeprom_read_block(void *buf, const void *addr, uint32_t len) {
+void eeprom_read_block(void *buf, const void *addr, size_t len) {
     const uint8_t *p    = (const uint8_t *)addr;
     uint8_t *      dest = (uint8_t *)buf;
     while (len--) {
@@ -181,7 +181,7 @@ void eeprom_read_block(void *buf, const void *addr, uint32_t len) {
     }
 }
 
-void eeprom_write_block(const void *buf, void *addr, uint32_t len) {
+void eeprom_write_block(const void *buf, void *addr, size_t len) {
     uint8_t *      p   = (uint8_t *)addr;
     const uint8_t *src = (const uint8_t *)buf;
     while (len--) {
@@ -189,7 +189,7 @@ void eeprom_write_block(const void *buf, void *addr, uint32_t len) {
     }
 }
 
-void eeprom_update_block(const void *buf, void *addr, uint32_t len) {
+void eeprom_update_block(const void *buf, void *addr, size_t len) {
     uint8_t *      p   = (uint8_t *)addr;
     const uint8_t *src = (const uint8_t *)buf;
     while (len--) {
diff --git a/tmk_core/common/chibios/eeprom_teensy.c b/tmk_core/common/chibios/eeprom_teensy.c
index a4093fb3b..0fab9f73d 100644
--- a/tmk_core/common/chibios/eeprom_teensy.c
+++ b/tmk_core/common/chibios/eeprom_teensy.c
@@ -50,7 +50,17 @@
 // (aligned to 2 or 4 byte boundaries) has twice the endurance
 // compared to writing 8 bit bytes.
 //
-#    define EEPROM_SIZE 32
+#    ifndef EEPROM_SIZE
+#        define EEPROM_SIZE 32
+#    endif
+
+/*
+    ^^^ Here be dragons:
+        NXP AppNote AN4282 section 3.1 states that partitioning must only be done once.
+        Once EEPROM partitioning is done, the size is locked to this initial configuration.
+        Attempts to modify the EEPROM_SIZE setting may brick your board.
+*/
+
 
 // Writing unaligned 16 or 32 bit data is handled automatically when
 // this is defined, but at a cost of extra code size.  Without this,
@@ -517,8 +527,11 @@ void eeprom_write_block(const void *buf, void *addr, uint32_t len) {
 #else
 // No EEPROM supported, so emulate it
 
-#    define EEPROM_SIZE 32
-static uint8_t buffer[EEPROM_SIZE];
+#    ifndef EEPROM_SIZE
+#        include "eeconfig.h"
+#        define EEPROM_SIZE (((EECONFIG_SIZE+3)/4)*4)  // based off eeconfig's current usage, aligned to 4-byte sizes, to deal with LTO
+#    endif
+__attribute__((aligned(4))) static uint8_t buffer[EEPROM_SIZE];
 
 uint8_t eeprom_read_byte(const uint8_t *addr) {
     uint32_t offset = (uint32_t)addr;
@@ -540,7 +553,7 @@ uint32_t eeprom_read_dword(const uint32_t *addr) {
     return eeprom_read_byte(p) | (eeprom_read_byte(p + 1) << 8) | (eeprom_read_byte(p + 2) << 16) | (eeprom_read_byte(p + 3) << 24);
 }
 
-void eeprom_read_block(void *buf, const void *addr, uint32_t len) {
+void eeprom_read_block(void *buf, const void *addr, size_t len) {
     const uint8_t *p    = (const uint8_t *)addr;
     uint8_t *      dest = (uint8_t *)buf;
     while (len--) {
@@ -562,7 +575,7 @@ void eeprom_write_dword(uint32_t *addr, uint32_t value) {
     eeprom_write_byte(p, value >> 24);
 }
 
-void eeprom_write_block(const void *buf, void *addr, uint32_t len) {
+void eeprom_write_block(const void *buf, void *addr, size_t len) {
     uint8_t *      p   = (uint8_t *)addr;
     const uint8_t *src = (const uint8_t *)buf;
     while (len--) {
@@ -589,7 +602,7 @@ void eeprom_update_dword(uint32_t *addr, uint32_t value) {
     eeprom_write_byte(p, value >> 24);
 }
 
-void eeprom_update_block(const void *buf, void *addr, uint32_t len) {
+void eeprom_update_block(const void *buf, void *addr, size_t len) {
     uint8_t *      p   = (uint8_t *)addr;
     const uint8_t *src = (const uint8_t *)buf;
     while (len--) {
diff --git a/tmk_core/common/eeconfig.c b/tmk_core/common/eeconfig.c
index 7cec4bd7d..fe56c57d1 100644
--- a/tmk_core/common/eeconfig.c
+++ b/tmk_core/common/eeconfig.c
@@ -9,6 +9,10 @@
 #    include "eeprom_stm32.h"
 #endif
 
+#if defined(EEPROM_DRIVER)
+#    include "eeprom_driver.h"
+#endif
+
 /** \brief eeconfig enable
  *
  * FIXME: needs doc
@@ -32,6 +36,9 @@ void eeconfig_init_quantum(void) {
 #ifdef STM32_EEPROM_ENABLE
     EEPROM_Erase();
 #endif
+#if defined(EEPROM_DRIVER)
+    eeprom_driver_erase();
+#endif
     eeprom_update_word(EECONFIG_MAGIC, EECONFIG_MAGIC_NUMBER);
     eeprom_update_byte(EECONFIG_DEBUG, 0);
     eeprom_update_byte(EECONFIG_DEFAULT_LAYER, 0);
@@ -81,6 +88,9 @@ void eeconfig_disable(void) {
 #ifdef STM32_EEPROM_ENABLE
     EEPROM_Erase();
 #endif
+#if defined(EEPROM_DRIVER)
+    eeprom_driver_erase();
+#endif
     eeprom_update_word(EECONFIG_MAGIC, EECONFIG_MAGIC_NUMBER_OFF);
 }
 
diff --git a/tmk_core/common/eeprom.h b/tmk_core/common/eeprom.h
index fcd1667c0..8a81e7066 100644
--- a/tmk_core/common/eeprom.h
+++ b/tmk_core/common/eeprom.h
@@ -1,23 +1,24 @@
 #ifndef TMK_CORE_COMMON_EEPROM_H_
 #define TMK_CORE_COMMON_EEPROM_H_
 
-#if defined(__AVR__)
+#if defined(__AVR__) && !defined(EEPROM_DRIVER)
 #    include <avr/eeprom.h>
 #else
 #    include <stdint.h>
+#    include <stdlib.h>
 
 uint8_t  eeprom_read_byte(const uint8_t *__p);
 uint16_t eeprom_read_word(const uint16_t *__p);
 uint32_t eeprom_read_dword(const uint32_t *__p);
-void     eeprom_read_block(void *__dst, const void *__src, uint32_t __n);
+void     eeprom_read_block(void *__dst, const void *__src, size_t __n);
 void     eeprom_write_byte(uint8_t *__p, uint8_t __value);
 void     eeprom_write_word(uint16_t *__p, uint16_t __value);
 void     eeprom_write_dword(uint32_t *__p, uint32_t __value);
-void     eeprom_write_block(const void *__src, void *__dst, uint32_t __n);
+void     eeprom_write_block(const void *__src, void *__dst, size_t __n);
 void     eeprom_update_byte(uint8_t *__p, uint8_t __value);
 void     eeprom_update_word(uint16_t *__p, uint16_t __value);
 void     eeprom_update_dword(uint32_t *__p, uint32_t __value);
-void     eeprom_update_block(const void *__src, void *__dst, uint32_t __n);
+void     eeprom_update_block(const void *__src, void *__dst, size_t __n);
 #endif
 
 #endif /* TMK_CORE_COMMON_EEPROM_H_ */
diff --git a/tmk_core/common/test/eeprom.c b/tmk_core/common/test/eeprom.c
index 44a0bf4d7..5c8e69dae 100644
--- a/tmk_core/common/test/eeprom.c
+++ b/tmk_core/common/test/eeprom.c
@@ -40,7 +40,7 @@ uint32_t eeprom_read_dword(const uint32_t *addr) {
     return eeprom_read_byte(p) | (eeprom_read_byte(p + 1) << 8) | (eeprom_read_byte(p + 2) << 16) | (eeprom_read_byte(p + 3) << 24);
 }
 
-void eeprom_read_block(void *buf, const void *addr, uint32_t len) {
+void eeprom_read_block(void *buf, const void *addr, size_t len) {
     const uint8_t *p    = (const uint8_t *)addr;
     uint8_t *      dest = (uint8_t *)buf;
     while (len--) {
@@ -62,7 +62,7 @@ void eeprom_write_dword(uint32_t *addr, uint32_t value) {
     eeprom_write_byte(p, value >> 24);
 }
 
-void eeprom_write_block(const void *buf, void *addr, uint32_t len) {
+void eeprom_write_block(const void *buf, void *addr, size_t len) {
     uint8_t *      p   = (uint8_t *)addr;
     const uint8_t *src = (const uint8_t *)buf;
     while (len--) {
@@ -86,7 +86,7 @@ void eeprom_update_dword(uint32_t *addr, uint32_t value) {
     eeprom_write_byte(p, value >> 24);
 }
 
-void eeprom_update_block(const void *buf, void *addr, uint32_t len) {
+void eeprom_update_block(const void *buf, void *addr, size_t len) {
     uint8_t *      p   = (uint8_t *)addr;
     const uint8_t *src = (const uint8_t *)buf;
     while (len--) {