feat: Add double tap to enter bootloader functionality

Add ability to enter the bootloader if double tapping reset within the
specified window.

app/Kconfig.defaults

@@ -110,4 +110,5 @@ config ZMK_BATTERY_REPORT_INTERVAL
     default 60
 
 # Imports
+rsource "src/boot/Kconfig.defaults"
 rsource "src/split/Kconfig.defaults"

app/src/boot/CMakeLists.txt

@@ -1,2 +1,3 @@
 
 target_sources_ifdef(CONFIG_ZMK_BOOTMODE_TO_MAGIC_VALUE_MAPPER app PRIVATE bootmode_to_magic_mapper.c)
+target_sources_ifdef(CONFIG_ZMK_DBL_TAP_BOOTLOADER app PRIVATE dbl_tap_bootloader.c)

app/src/boot/Kconfig

@@ -1,4 +1,18 @@
 
+config ZMK_DBL_TAP_BOOTLOADER
+    bool "Double Tap To Enter Bootloader"
+    depends on RETENTION_BOOT_MODE
+
+if ZMK_DBL_TAP_BOOTLOADER
+
+config ZMK_DBL_TAP_BOOTLOADER_TIMEOUT_MS
+    int "Double Tap Timeout (ms)"
+
+config ZMK_DBL_TAP_BOOTLOADER_INIT_PRIORITY
+    int "Double Tap Init Priority"
+
+endif
+
 config ZMK_BOOTMODE_TO_MAGIC_VALUE_MAPPER
     bool "Magic Value Mapper"
     default y
@@ -25,7 +39,5 @@ endchoice
 
 config ZMK_BOOTMODE_BOOTLOADER_MAGIC_VALUE
     hex
-    default 0xf01669ef if ZMK_BOOTMODE_MAGIC_VALUE_BOOTLOADER_TYPE_TINYUF2 || ZMK_BOOTMODE_MAGIC_VALUE_BOOTLOADER_TYPE_ADAFRUIT_BOSSA || BOOTLOADER_BOSSA_ADAFRUIT_UF2
-    default 0x57 if ZMK_BOOTMODE_MAGIC_VALUE_BOOTLOADER_TYPE_ADAFRUIT_NRF52
 
 endif

app/src/boot/Kconfig.defaults

@@ -0,0 +1,27 @@
+
+config ZMK_DBL_TAP_BOOTLOADER
+    default y if STM32_BOOTLOADER || RPI_PICO_ROM_BOOTLOADER
+    depends on RETENTION_BOOT_MODE
+
+if ZMK_DBL_TAP_BOOTLOADER
+
+config ZMK_DBL_TAP_BOOTLOADER_TIMEOUT_MS
+    default 500
+
+config ZMK_DBL_TAP_BOOTLOADER_INIT_PRIORITY
+    default 20
+
+endif
+
+if ZMK_BOOTMODE_TO_MAGIC_VALUE_MAPPER
+
+choice ZMK_BOOTMODE_MAGIC_VALUE_BOOTLOADER_TYPE
+    default ZMK_BOOTMODE_MAGIC_VALUE_BOOTLOADER_TYPE_ADAFRUIT_NRF52 if SOC_NRF52840
+
+endchoice
+
+config ZMK_BOOTMODE_BOOTLOADER_MAGIC_VALUE
+    default 0xf01669ef if ZMK_BOOTMODE_MAGIC_VALUE_BOOTLOADER_TYPE_TINYUF2 || ZMK_BOOTMODE_MAGIC_VALUE_BOOTLOADER_TYPE_ADAFRUIT_BOSSA || BOOTLOADER_BOSSA_ADAFRUIT_UF2
+    default 0x57 if ZMK_BOOTMODE_MAGIC_VALUE_BOOTLOADER_TYPE_ADAFRUIT_NRF52
+
+endif

app/src/boot/dbl_tap_bootloader.c

@@ -0,0 +1,16 @@
+#include <soc.h>
+#include <zephyr/init.h>
+#include <zephyr/retention/retention.h>
+#include <zephyr/retention/bootmode.h>
+
+static int dbl_tap_boot_mode_init(void) {
+    bootmode_set(BOOT_MODE_TYPE_BOOTLOADER);
+
+    k_busy_wait(CONFIG_ZMK_DBL_TAP_BOOTLOADER_TIMEOUT_MS * 1000);
+
+    bootmode_clear();
+
+    return 0;
+}
+
+SYS_INIT(dbl_tap_boot_mode_init, POST_KERNEL, CONFIG_ZMK_DBL_TAP_BOOTLOADER_INIT_PRIORITY);