Added external spi flash driver.

common_features.mk

@@ -201,6 +201,21 @@ else
   endif
 endif
 
+VALID_FLASH_DRIVER_TYPES := spi
+FLASH_DRIVER ?= no
+ifneq ($(strip $(FLASH_DRIVER)), no)
+    ifeq ($(filter $(FLASH_DRIVER),$(VALID_FLASH_DRIVER_TYPES)),)
+        $(error FLASH_DRIVER="$(FLASH_DRIVER)" is not a valid FLASH driver)
+    else
+        OPT_DEFS += -DFLASH_ENABLE
+        ifeq ($(strip $(FLASH_DRIVER)), spi)
+            OPT_DEFS += -DFLASH_DRIVER -DFLASH_SPI
+            COMMON_VPATH += $(DRIVER_PATH)/flash
+            SRC += flash_spi.c
+        endif
+    endif
+endif
+
 RGBLIGHT_ENABLE ?= no
 VALID_RGBLIGHT_TYPES := WS2812 APA102 custom
 

docs/flash_driver.md

@@ -0,0 +1,24 @@
+# FLASH Driver Configuration :id=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 :id=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`
+
+!> All the above default configurations are based on MX25L4006E NOR Flash.