QMK Apple Fn

readme.md

QMK Apple Fn Key

This patch adds support for the Apple Fn key, which unlike most keyboards with Fn keys, is actually sent over the wire. It works by repurposing the reserved byte in the keyboard report to represent the KeyboardFn usage of the AppleVendor Top Case usage page. When the Fn key is pressed, the value of this byte becomes 1.

To apply this patch, download the below file, cd to your qmk_firmware repository in your preferred terminal, and run git apply /path/to/applefn.patch. Then, add the QK_APPLE_FN keycode (or AP_FN for short) to your keymap.

There are a couple of caveats to this implementation that are important to be aware of. Firstly, it is not compatible with NKRO, as QMK's NKRO report format has no reserved byte - it is part of the 6KRO report for compatibility with the HID boot protocol. Thus you must set NKRO_ENABLE = no in your keymap's rules.mk. You will also need to redefine the USB Vendor and Product IDs in your keymap's config.h to that of a genuine Apple keyboard* in order for macOS to recognise the Fn key:

#undef VENDOR_ID
#define VENDOR_ID 0x05AC
#undef PRODUCT_ID
#define PRODUCT_ID <pid>

This is the primary reason this patch has not been integrated into upstream QMK - Apple would probably not be too happy about others using their vendor ID, and a feature that relies on the VID/PID pair being set to a specific value is not particularly ideal anyway.

See qmk/qmk_firmware#2179 for a little more info and discussion.

^{* It appears that the functionality of certain F keys can differ depending on the PID, likely because they have evolved over time on real Apple keyboards.}

applefn.patch

diff --git a/builddefs/common_features.mk b/builddefs/common_features.mk
index 18f8b0bbfc..4ef3e230e4 100644
--- a/builddefs/common_features.mk
+++ b/builddefs/common_features.mk
@@ -878,6 +878,10 @@ ifeq ($(strip $(JOYSTICK_ENABLE)), yes)
     endif
 endif
 
+ifeq ($(strip $(APPLE_FN_ENABLE)), yes)
+    OPT_DEFS += -DAPPLE_FN_ENABLE
+endif
+
 USBPD_ENABLE ?= no
 VALID_USBPD_DRIVER_TYPES = custom vendor
 USBPD_DRIVER ?= vendor
diff --git a/data/constants/keycodes/keycodes_0.0.2_applefn.hjson b/data/constants/keycodes/keycodes_0.0.2_applefn.hjson
new file mode 100644
index 0000000000..1378413a9e
--- /dev/null
+++ b/data/constants/keycodes/keycodes_0.0.2_applefn.hjson
@@ -0,0 +1,11 @@
+{
+    "keycodes": {
+        "0x5300": {
+            "group": "apple_fn",
+            "key": "QK_APPLE_FN",
+            "aliases": [
+                "AP_FN"
+            ]
+        }
+    }
+}
diff --git a/quantum/action.c b/quantum/action.c
index 6368f7398c..d9bd34f681 100644
--- a/quantum/action.c
+++ b/quantum/action.c
@@ -555,6 +555,18 @@ void process_action(keyrecord_t *record, action_t action) {
             }
             break;
 #endif // EXTRAKEY_ENABLE
+#ifdef APPLE_FN_ENABLE
+        /* Apple Fn */
+        case ACT_APPLE_FN:
+            if (event.pressed) {
+                add_apple_fn(keyboard_report);
+                send_keyboard_report();
+            } else {
+                del_apple_fn(keyboard_report);
+                send_keyboard_report();
+            }
+            break;
+#endif
         /* Mouse key */
         case ACT_MOUSEKEY:
             register_mouse(action.key.code, event.pressed);
@@ -1196,6 +1208,9 @@ void debug_action(action_t action) {
         case ACT_USAGE:
             ac_dprintf("ACT_USAGE");
             break;
+        case ACT_APPLE_FN:
+            dprint("ACT_APPLE_FN");
+            break;
         case ACT_MOUSEKEY:
             ac_dprintf("ACT_MOUSEKEY");
             break;
diff --git a/quantum/action_code.h b/quantum/action_code.h
index d9a575b518..f347010c8d 100644
--- a/quantum/action_code.h
+++ b/quantum/action_code.h
@@ -53,7 +53,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
  * ACT_SWAP_HANDS(0110):
  * 0110|xxxx| keycode     Swap hands (keycode on tap, or options)
  *
- * 0111|xxxx xxxx xxxx    (reserved)
+ * ACT_APPLE_FN(0111):
+ * 0111|0000|0000|0000    Apple Fn
  *
  * Layer Actions(10xx)
  * -------------------
@@ -95,6 +96,8 @@ enum action_kind_id {
     ACT_MOUSEKEY = 0b0101,
     /* One-hand Support */
     ACT_SWAP_HANDS = 0b0110,
+    /* Apple Fn */
+    ACT_APPLE_FN = 0b0111,
     /* Layer Actions */
     ACT_LAYER         = 0b1000,
     ACT_LAYER_MODS    = 0b1001,
@@ -182,6 +185,7 @@ enum usage_pages {
 
 #define ACTION_USAGE_SYSTEM(id) ACTION(ACT_USAGE, PAGE_SYSTEM << 10 | (id))
 #define ACTION_USAGE_CONSUMER(id) ACTION(ACT_USAGE, PAGE_CONSUMER << 10 | (id))
+#define ACTION_APPLE_FN() ACTION(ACT_APPLE_FN, 0)
 #define ACTION_MOUSEKEY(key) ACTION(ACT_MOUSEKEY, key)
 
 /** \brief Layer Actions
diff --git a/quantum/keycodes.h b/quantum/keycodes.h
index bbf10da36d..b8e894a399 100644
--- a/quantum/keycodes.h
+++ b/quantum/keycodes.h
@@ -310,6 +310,7 @@ enum qk_keycode_defines {
     KC_RIGHT_SHIFT = 0x00E5,
     KC_RIGHT_ALT = 0x00E6,
     KC_RIGHT_GUI = 0x00E7,
+    QK_APPLE_FN = 0x5300,
     QK_SWAP_HANDS_TOGGLE = 0x56F0,
     QK_SWAP_HANDS_TAP_TOGGLE = 0x56F1,
     QK_SWAP_HANDS_MOMENTARY_ON = 0x56F2,
@@ -938,6 +939,7 @@ enum qk_keycode_defines {
     KC_RGUI    = KC_RIGHT_GUI,
     KC_RCMD    = KC_RIGHT_GUI,
     KC_RWIN    = KC_RIGHT_GUI,
+    AP_FN      = QK_APPLE_FN,
     SH_TOGG    = QK_SWAP_HANDS_TOGGLE,
     SH_TT      = QK_SWAP_HANDS_TAP_TOGGLE,
     SH_MON     = QK_SWAP_HANDS_MOMENTARY_ON,
@@ -1406,6 +1408,7 @@ enum qk_keycode_defines {
 #define IS_CONSUMER_KEYCODE(code) ((code) >= KC_AUDIO_MUTE && (code) <= KC_LAUNCHPAD)
 #define IS_MOUSE_KEYCODE(code) ((code) >= KC_MS_UP && (code) <= KC_MS_ACCEL2)
 #define IS_MODIFIER_KEYCODE(code) ((code) >= KC_LEFT_CTRL && (code) <= KC_RIGHT_GUI)
+#define IS_APPLE_FN_KEYCODE(code) ((code) >= QK_APPLE_FN && (code) <= QK_APPLE_FN)
 #define IS_SWAP_HANDS_KEYCODE(code) ((code) >= QK_SWAP_HANDS_TOGGLE && (code) <= QK_SWAP_HANDS_ONE_SHOT)
 #define IS_MAGIC_KEYCODE(code) ((code) >= QK_MAGIC_SWAP_CONTROL_CAPS_LOCK && (code) <= QK_MAGIC_TOGGLE_ESCAPE_CAPS_LOCK)
 #define IS_MIDI_KEYCODE(code) ((code) >= QK_MIDI_ON && (code) <= QK_MIDI_PITCH_BEND_UP)
diff --git a/quantum/keymap_common.c b/quantum/keymap_common.c
index 9a67fad278..36a0b309be 100644
--- a/quantum/keymap_common.c
+++ b/quantum/keymap_common.c
@@ -70,6 +70,11 @@ action_t action_for_keycode(uint16_t keycode) {
         case KC_AUDIO_MUTE ... KC_LAUNCHPAD:
             action.code = ACTION_USAGE_CONSUMER(KEYCODE2CONSUMER(keycode));
             break;
+#endif
+#ifdef APPLE_FN_ENABLE
+        case QK_APPLE_FN:
+            action.code = ACTION_APPLE_FN();
+            break;
 #endif
         case KC_MS_UP ... KC_MS_ACCEL2:
             action.code = ACTION_MOUSEKEY(keycode);
diff --git a/tmk_core/protocol/report.c b/tmk_core/protocol/report.c
index 1ba3be4604..b53d3f687b 100644
--- a/tmk_core/protocol/report.c
+++ b/tmk_core/protocol/report.c
@@ -299,3 +299,13 @@ __attribute__((weak)) bool has_mouse_report_changed(report_mouse_t* new_report,
     return changed;
 }
 #endif
+
+#ifdef APPLE_FN_ENABLE
+void add_apple_fn(report_keyboard_t* keyboard_report) {
+    keyboard_report->reserved = 1;
+}
+
+void del_apple_fn(report_keyboard_t* keyboard_report) {
+    keyboard_report->reserved = 0;
+}
+#endif
diff --git a/tmk_core/protocol/report.h b/tmk_core/protocol/report.h
index 9d415a3bfd..8c65b40386 100644
--- a/tmk_core/protocol/report.h
+++ b/tmk_core/protocol/report.h
@@ -348,6 +348,11 @@ void clear_keys_from_report(report_keyboard_t* keyboard_report);
 bool has_mouse_report_changed(report_mouse_t* new_report, report_mouse_t* old_report);
 #endif
 
+#ifdef APPLE_FN_ENABLE
+void add_apple_fn(report_keyboard_t* keyboard_report);
+void del_apple_fn(report_keyboard_t* keyboard_report);
+#endif
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/tmk_core/protocol/usb_descriptor.c b/tmk_core/protocol/usb_descriptor.c
index e215c90900..e38c0d37f7 100644
--- a/tmk_core/protocol/usb_descriptor.c
+++ b/tmk_core/protocol/usb_descriptor.c
@@ -75,10 +75,22 @@ const USB_Descriptor_HIDReport_Datatype_t PROGMEM KeyboardReport[] = {
         HID_RI_REPORT_COUNT(8, 0x08),
         HID_RI_REPORT_SIZE(8, 0x01),
         HID_RI_INPUT(8, HID_IOF_DATA | HID_IOF_VARIABLE | HID_IOF_ABSOLUTE),
+
+#ifdef APPLE_FN_ENABLE
+        HID_RI_USAGE_PAGE(8, 0xFF),    // AppleVendor Top Case
+        HID_RI_USAGE(8, 0x03),         // KeyboardFn
+        HID_RI_LOGICAL_MINIMUM(8, 0x00),
+        HID_RI_LOGICAL_MAXIMUM(8, 0x01),
+        HID_RI_REPORT_COUNT(8, 0x01),
+        HID_RI_REPORT_SIZE(8, 0x08),
+        HID_RI_INPUT(8, HID_IOF_DATA | HID_IOF_VARIABLE | HID_IOF_ABSOLUTE),
+#else
         // Reserved (1 byte)
         HID_RI_REPORT_COUNT(8, 0x01),
         HID_RI_REPORT_SIZE(8, 0x08),
         HID_RI_INPUT(8, HID_IOF_CONSTANT),
+#endif
+
         // Keycodes (6 bytes)
         HID_RI_USAGE_PAGE(8, 0x07),    // Keyboard/Keypad
         HID_RI_USAGE_MINIMUM(8, 0x00),
diff --git a/tmk_core/protocol/vusb/vusb.c b/tmk_core/protocol/vusb/vusb.c
index d74f375f66..2ade1350ad 100644
--- a/tmk_core/protocol/vusb/vusb.c
+++ b/tmk_core/protocol/vusb/vusb.c
@@ -417,10 +417,22 @@ const PROGMEM uchar keyboard_hid_report[] = {
     0x95, 0x08, //   Report Count (8)
     0x75, 0x01, //   Report Size (1)
     0x81, 0x02, //   Input (Data, Variable, Absolute)
+
+#ifdef APPLE_FN_ENABLE
+    0x05, 0xFF,  //   Usage Page (AppleVendor Top Case)
+    0x09, 0x03,  //   Usage (KeyboardFn)
+    0x15, 0x00,  //   Logical Minimum (0)
+    0x25, 0x01,  //   Logical Maximum (1)
+    0x95, 0x01,  //   Report Count (1)
+    0x75, 0x08,  //   Report Size (8)
+    0x81, 0x02,  //   Input (Data, Variable, Absolute)
+#else
     // Reserved (1 byte)
     0x95, 0x01, //   Report Count (1)
     0x75, 0x08, //   Report Size (8)
     0x81, 0x03, //   Input (Constant)
+#endif
+
     // Keycodes (6 bytes)
     0x05, 0x07,       //   Usage Page (Keyboard/Keypad)
     0x19, 0x00,       //   Usage Minimum (0)

Yes, thank you. SHARED_EP was the missing step. Now working as expected. I will make an up to date gist later.

Now, if only I could get the keyboard setting to let me use this thing as a generic modifier key.

Here's the 2024 version of the patch