5 files changed, 111 insertions, 5 deletions

diff --git a/docs/_summary.md b/docs/_summary.md
index e35125109..d47b252c0 100644
--- a/docs/_summary.md
+++ b/docs/_summary.md
@@ -136,6 +136,10 @@
       * [Development Environment](api_development_environment.md)
       * [Architecture Overview](api_development_overview.md)
 
+  * Hardware Platform Development
+    * Arm/ChibiOS
+      * [Early initialization](platformdev_chibios_earlyinit.md)
+
   * QMK Reference
     * [Contributing to QMK](contributing.md)
     * [Translating the QMK Docs](translating.md)
diff --git a/docs/platformdev_chibios_earlyinit.md b/docs/platformdev_chibios_earlyinit.md
new file mode 100644
index 000000000..699c22377
--- /dev/null
+++ b/docs/platformdev_chibios_earlyinit.md
@@ -0,0 +1,53 @@
+# Arm/ChibiOS Early Initialization :id=chibios-early-init
+
+This page describes a part of QMK that is a somewhat advanced concept, and is only relevant to keyboard designers.
+
+QMK uses ChibiOS as the underlying layer to support a multitude of Arm-based devices. Each ChibiOS-supported keyboard has a low-level board definition which is responsible for initializing hardware peripherals such as the clocks, and GPIOs.
+
+Older QMK revisions required duplication of these board definitions inside your keyboard's directory in order to override such early initialization points; this is now abstracted into the following APIs, and allows usage of the board definitions supplied with ChibiOS itself. Check `<qmk_firmware>/lib/chibios/os/hal/boards` for the list of official definitions. If your keyboard needs extra initialization at a very early stage, consider providing keyboard-level overrides of the following APIs:
+
+## `early_hardware_init_pre()` :id=early-hardware-init-pre
+
+The function `early_hardware_init_pre` is the earliest possible code that can be executed by a keyboard firmware. This is intended as a replacement for the ChibiOS board definition's `__early_init` function, and is the equivalent of executing at the start of the function.
+
+This is executed before RAM gets cleared, and before clocks or GPIOs are configured; any delays or preparation using GPIOs is not likely to work at this point. After executing this function, RAM on the MCU may be zero'ed. Assigning values to variables during execution of this function may be overwritten.
+
+As such, if you wish to override this API consider limiting use to writing to low-level registers. The default implementation of this function can be configured to jump to bootloader if a `RESET` key was pressed, by ensuring `#define EARLY_INIT_PERFORM_BOOTLOADER_JUMP TRUE` is in the keyboard's `config.h` file.
+
+To implement your own version of this function, in your keyboard's source files:
+
+```c
+void early_hardware_init_pre(void) {
+    // do things with registers
+}
+```
+
+## `early_hardware_init_post()` :id=early-hardware-init-post
+
+The function `early_hardware_init_post` is the next earliest possible code that can be executed by a keyboard firmware. This is executed after RAM has been cleared, and clocks and GPIOs are configured. This is intended as a replacement for the ChibiOS board definition's `__early_init` function, and is the equivalent of executing at the end of the function.
+
+Much like `early_hardware_init_pre`, ChibiOS has not yet been initialized either, so the same restrictions on delays and timing apply.
+
+If you wish to override this API, consider limiting functionality to register writes, variable initialization, and GPIO toggling. The default implementation of this function is to do nothing.
+
+To implement your own version of this function, in your keyboard's source files:
+
+```c
+void early_hardware_init_post(void) {
+    // toggle GPIO pins and write to variables
+}
+```
+
+## `board_init()` :id=board-init
+
+The function `board_init` is executed directly after the ChibiOS initialization routines have completed. At this stage, all normal low-level functionality should be available for use (including timers and delays), with the restriction that USB is not yet connected. This is intended as a replacement for the ChibiOS board definition's `boardInit` function.
+
+The default implementation of this function is to do nothing.
+
+To implement your own version of this function, in your keyboard's source files:
+
+```c
+void board_init(void) {
+    // initialize anything that requires ChibiOS
+}
+```
\ No newline at end of file
diff --git a/tmk_core/protocol/chibios/init_hooks.h b/tmk_core/protocol/chibios/init_hooks.h
new file mode 100644
index 000000000..fffced913
--- /dev/null
+++ b/tmk_core/protocol/chibios/init_hooks.h
@@ -0,0 +1,5 @@
+#pragma once
+
+// Override the initialisation functions inside the ChibiOS board.c files
+#define __early_init __chibios_override___early_init
+#define boardInit __chibios_override_boardInit
diff --git a/tmk_core/protocol/chibios/main.c b/tmk_core/protocol/chibios/main.c
index 6479fd09d..61665eb6f 100644
--- a/tmk_core/protocol/chibios/main.c
+++ b/tmk_core/protocol/chibios/main.c
@@ -33,6 +33,11 @@
 #include "debug.h"
 #include "printf.h"
 
+#ifndef EARLY_INIT_PERFORM_BOOTLOADER_JUMP
+// Change this to be TRUE once we've migrated keyboards to the new init system
+#    define EARLY_INIT_PERFORM_BOOTLOADER_JUMP FALSE
+#endif
+
 #ifdef SLEEP_LED_ENABLE
 #    include "sleep_led.h"
 #endif
@@ -101,6 +106,39 @@ void midi_ep_task(void);
 //   }
 // }
 
+/* Early initialisation
+ */
+__attribute__((weak)) void early_hardware_init_pre(void) {
+#if EARLY_INIT_PERFORM_BOOTLOADER_JUMP
+    void enter_bootloader_mode_if_requested(void);
+    enter_bootloader_mode_if_requested();
+#endif  // EARLY_INIT_PERFORM_BOOTLOADER_JUMP
+}
+
+__attribute__((weak)) void early_hardware_init_post(void) {}
+
+__attribute__((weak)) void board_init(void) {}
+
+// This overrides what's normally in ChibiOS board definitions
+void __early_init(void) {
+    early_hardware_init_pre();
+
+    // This is the renamed equivalent of __early_init in the board.c file
+    void __chibios_override___early_init(void);
+    __chibios_override___early_init();
+
+    early_hardware_init_post();
+}
+
+// This overrides what's normally in ChibiOS board definitions
+void boardInit(void) {
+    // This is the renamed equivalent of boardInit in the board.c file
+    void __chibios_override_boardInit(void);
+    __chibios_override_boardInit();
+
+    board_init();
+}
+
 /* Main thread
  */
 int main(void) {
diff --git a/tmk_core/rules.mk b/tmk_core/rules.mk
index c1474a5c2..a66718cd2 100644
--- a/tmk_core/rules.mk
+++ b/tmk_core/rules.mk
@@ -223,6 +223,12 @@ $(foreach LOBJ, $(NO_LTO_OBJ), $(eval $(call NO_LTO,$(LOBJ))))
 
 MOVE_DEP = mv -f $(patsubst %.o,%.td,$@) $(patsubst %.o,%.d,$@)
 
+# For a ChibiOS build, ensure that the board files have the hook overrides injected
+define BOARDSRC_INJECT_HOOKS
+$(KEYBOARD_OUTPUT)/$(patsubst %.c,%.o,$(patsubst ./%,%,$1)): INIT_HOOK_CFLAGS += -include $(TOP_DIR)/tmk_core/protocol/chibios/init_hooks.h
+endef
+$(foreach LOBJ, $(BOARDSRC), $(eval $(call BOARDSRC_INJECT_HOOKS,$(LOBJ))))
+
 # Add QMK specific flags
 DFU_SUFFIX ?= dfu-suffix
 DFU_SUFFIX_ARGS ?=
@@ -306,27 +312,27 @@ ifdef $1_CONFIG
 $1_CONFIG_FLAGS += $$(patsubst %,-include %,$$($1_CONFIG))
 endif
 $1_CFLAGS = $$(ALL_CFLAGS) $$($1_DEFS) $$($1_INCFLAGS) $$($1_CONFIG_FLAGS) $$(NOLTO_CFLAGS)
-$1_CXXFLAGS= $$(ALL_CXXFLAGS) $$($1_DEFS) $$($1_INCFLAGS) $$($1_CONFIG_FLAGS) $$(NOLTO_CFLAGS)
-$1_ASFLAGS= $$(ALL_ASFLAGS) $$($1_DEFS) $$($1_INCFLAGS) $$($1_CONFIG_FLAGS)
+$1_CXXFLAGS = $$(ALL_CXXFLAGS) $$($1_DEFS) $$($1_INCFLAGS) $$($1_CONFIG_FLAGS) $$(NOLTO_CFLAGS)
+$1_ASFLAGS = $$(ALL_ASFLAGS) $$($1_DEFS) $$($1_INCFLAGS) $$($1_CONFIG_FLAGS)
 
 # Compile: create object files from C source files.
 $1/%.o : %.c $1/%.d $1/cflags.txt $1/compiler.txt | $(BEGIN)
         @mkdir -p $$(@D)
         @$$(SILENT) || printf "$$(MSG_COMPILING) $$<" | $$(AWK_CMD)
-        $$(eval CMD := $$(CC) -c $$($1_CFLAGS) $$(GENDEPFLAGS) $$< -o $$@ && $$(MOVE_DEP))
+        $$(eval CMD := $$(CC) -c $$($1_CFLAGS) $$(INIT_HOOK_CFLAGS) $$(GENDEPFLAGS) $$< -o $$@ && $$(MOVE_DEP))
         @$$(BUILD_CMD)
 
 # Compile: create object files from C++ source files.
 $1/%.o : %.cpp $1/%.d $1/cxxflags.txt $1/compiler.txt | $(BEGIN)
         @mkdir -p $$(@D)
         @$$(SILENT) || printf "$$(MSG_COMPILING_CXX) $$<" | $$(AWK_CMD)
-        $$(eval CMD=$$(CC) -c $$($1_CXXFLAGS) $$(GENDEPFLAGS) $$< -o $$@ && $$(MOVE_DEP))
+        $$(eval CMD=$$(CC) -c $$($1_CXXFLAGS) $$(INIT_HOOK_CFLAGS) $$(GENDEPFLAGS) $$< -o $$@ && $$(MOVE_DEP))
         @$$(BUILD_CMD)
 
 $1/%.o : %.cc $1/%.d $1/cxxflags.txt $1/compiler.txt | $(BEGIN)
         @mkdir -p $$(@D)
         @$$(SILENT) || printf "$$(MSG_COMPILING_CXX) $$<" | $$(AWK_CMD)
-        $$(eval CMD=$$(CC) -c $$($1_CXXFLAGS) $$(GENDEPFLAGS) $$< -o $$@ && $$(MOVE_DEP))
+        $$(eval CMD=$$(CC) -c $$($1_CXXFLAGS) $$(INIT_HOOK_CFLAGS) $$(GENDEPFLAGS) $$< -o $$@ && $$(MOVE_DEP))
         @$$(BUILD_CMD)
 
 # Assemble: create object files from assembler source files.