refactor: Move to zmk_hid_indicators_t type.

app/CMakeLists.txt

@@ -68,6 +68,7 @@ if ((NOT CONFIG_ZMK_SPLIT) OR CONFIG_ZMK_SPLIT_ROLE_CENTRAL)
   target_sources(app PRIVATE src/events/layer_state_changed.c)
   target_sources(app PRIVATE src/events/modifiers_state_changed.c)
   target_sources(app PRIVATE src/events/keycode_state_changed.c)
+  target_sources_ifdef(CONFIG_ZMK_HID_INDICATORS app PRIVATE src/hid_indicators.c)
 
   if (CONFIG_ZMK_BLE)
     target_sources(app PRIVATE src/events/ble_active_profile_changed.c)
@@ -83,6 +84,8 @@ target_sources_ifdef(CONFIG_ZMK_BACKLIGHT app PRIVATE src/behaviors/behavior_bac
 target_sources_ifdef(CONFIG_ZMK_BATTERY_REPORTING app PRIVATE src/events/battery_state_changed.c)
 target_sources_ifdef(CONFIG_ZMK_BATTERY_REPORTING app PRIVATE src/battery.c)
 
+target_sources_ifdef(CONFIG_ZMK_HID_INDICATORS app PRIVATE src/events/hid_indicators_changed.c)
+
 target_sources_ifdef(CONFIG_ZMK_SPLIT app PRIVATE src/events/split_peripheral_status_changed.c)
 add_subdirectory(src/split)
 

app/Kconfig

@@ -87,6 +87,12 @@ config ZMK_HID_CONSUMER_REPORT_USAGES_BASIC
 
 endchoice
 
+config ZMK_HID_INDICATORS
+    bool "HID Indicators"
+    help
+      Enable HID indicators, used for detecting state of Caps/Scroll/Num Lock,
+      Kata, and Compose.
+
 menu "Output Types"
 
 config ZMK_USB

app/include/zmk/ble.h

@@ -27,6 +27,7 @@ int zmk_ble_prof_select(uint8_t index);
 int zmk_ble_prof_disconnect(uint8_t index);
 
 int zmk_ble_active_profile_index();
+int zmk_ble_profile_index(const bt_addr_le_t *addr);
 bt_addr_le_t *zmk_ble_active_profile_addr();
 bool zmk_ble_active_profile_is_open();
 bool zmk_ble_active_profile_is_connected();

app/include/zmk/events/hid_indicators_changed.h

@@ -0,0 +1,16 @@
+/*
+ * Copyright (c) 2022 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#pragma once
+
+#include <zmk/hid_indicators_types.h>
+#include <zmk/event_manager.h>
+
+struct zmk_hid_indicators_changed {
+    zmk_hid_indicators_t indicators;
+};
+
+ZMK_EVENT_DECLARE(zmk_hid_indicators_changed);

app/include/zmk/hid.h

@@ -50,6 +50,7 @@
 #define ZMK_HID_MAIN_VAL_BUFFERED_BYTES (0x01 << 8)
 
 #define ZMK_HID_REPORT_ID_KEYBOARD 0x01
+#define ZMK_HID_REPORT_ID_LEDS 0x01
 #define ZMK_HID_REPORT_ID_CONSUMER 0x02
 #define ZMK_HID_REPORT_ID_MOUSE 0x03
 
@@ -73,6 +74,22 @@ static const uint8_t zmk_hid_report_desc[] = {
     HID_REPORT_COUNT(0x01),
     HID_INPUT(ZMK_HID_MAIN_VAL_CONST | ZMK_HID_MAIN_VAL_VAR | ZMK_HID_MAIN_VAL_ABS),
 
+#if IS_ENABLED(CONFIG_ZMK_HID_INDICATORS)
+
+    HID_USAGE_PAGE(HID_USAGE_LED),
+    HID_USAGE_MIN8(HID_USAGE_LED_NUM_LOCK),
+    HID_USAGE_MAX8(HID_USAGE_LED_KANA),
+    HID_REPORT_SIZE(0x01),
+    HID_REPORT_COUNT(0x05),
+    HID_OUTPUT(ZMK_HID_MAIN_VAL_DATA | ZMK_HID_MAIN_VAL_VAR | ZMK_HID_MAIN_VAL_ABS),
+
+    HID_USAGE_PAGE(HID_USAGE_LED),
+    HID_REPORT_SIZE(0x03),
+    HID_REPORT_COUNT(0x01),
+    HID_OUTPUT(ZMK_HID_MAIN_VAL_CONST | ZMK_HID_MAIN_VAL_VAR | ZMK_HID_MAIN_VAL_ABS),
+
+#endif // IS_ENABLED(CONFIG_ZMK_HID_INDICATORS)
+
     HID_USAGE_PAGE(HID_USAGE_KEY),
 
 #if IS_ENABLED(CONFIG_ZMK_HID_REPORT_TYPE_NKRO)
@@ -189,6 +206,19 @@ struct zmk_hid_keyboard_report {
     struct zmk_hid_keyboard_report_body body;
 } __packed;
 
+#if IS_ENABLED(CONFIG_ZMK_HID_INDICATORS)
+
+struct zmk_hid_led_report_body {
+    uint8_t leds;
+} __packed;
+
+struct zmk_hid_led_report {
+    uint8_t report_id;
+    struct zmk_hid_led_report_body body;
+} __packed;
+
+#endif // IS_ENABLED(CONFIG_ZMK_HID_INDICATORS)
+
 struct zmk_hid_consumer_report_body {
 #if IS_ENABLED(CONFIG_ZMK_HID_CONSUMER_REPORT_USAGES_BASIC)
     uint8_t keys[CONFIG_ZMK_HID_CONSUMER_REPORT_SIZE];

app/include/zmk/hid_indicators.h

@@ -0,0 +1,19 @@
+/*
+ * Copyright (c) 2022 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#pragma once
+
+#include <zmk/endpoints_types.h>
+#include <zmk/hid.h>
+#include <zmk/hid_indicators_types.h>
+
+zmk_hid_indicators_t zmk_hid_indicators_get_current_profile(void);
+zmk_hid_indicators_t zmk_hid_indicators_get_profile(struct zmk_endpoint_instance endpoint);
+void zmk_hid_indicators_set_profile(zmk_hid_indicators_t indicators,
+                                    struct zmk_endpoint_instance endpoint);
+
+void zmk_hid_indicators_process_report(struct zmk_hid_led_report_body *report,
+                                       struct zmk_endpoint_instance endpoint);

app/include/zmk/hid_indicators_types.h

@@ -0,0 +1,9 @@
+/*
+ * Copyright (c) 2022 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#pragma once
+
+typedef uint8_t zmk_hid_indicators_t;

app/include/zmk/split/bluetooth/central.h

@@ -4,5 +4,15 @@
 #include <zephyr/bluetooth/addr.h>
 #include <zmk/behavior.h>
 
+#if IS_ENABLED(CONFIG_ZMK_SPLIT_PERIPHERAL_HID_INDICATORS)
+#include <zmk/hid_indicators_types.h>
+#endif // IS_ENABLED(CONFIG_ZMK_SPLIT_PERIPHERAL_HID_INDICATORS)
+
 int zmk_split_bt_invoke_behavior(uint8_t source, struct zmk_behavior_binding *binding,
                                  struct zmk_behavior_binding_event event, bool state);
+
+#if IS_ENABLED(CONFIG_ZMK_SPLIT_PERIPHERAL_HID_INDICATORS)
+
+int zmk_split_bt_update_hid_indicator(zmk_hid_indicators_t indicators);
+
+#endif // IS_ENABLED(CONFIG_ZMK_SPLIT_PERIPHERAL_HID_INDICATORS)

app/include/zmk/split/bluetooth/uuid.h

@@ -17,3 +17,4 @@
 #define ZMK_SPLIT_BT_CHAR_POSITION_STATE_UUID ZMK_BT_SPLIT_UUID(0x00000001)
 #define ZMK_SPLIT_BT_CHAR_RUN_BEHAVIOR_UUID ZMK_BT_SPLIT_UUID(0x00000002)
 #define ZMK_SPLIT_BT_CHAR_SENSOR_STATE_UUID ZMK_BT_SPLIT_UUID(0x00000003)
+#define ZMK_SPLIT_BT_UPDATE_HID_INDICATORS_UUID ZMK_BT_SPLIT_UUID(0x00000004)

app/src/ble.c

@@ -224,6 +224,15 @@ int zmk_ble_clear_bonds() {
 
 int zmk_ble_active_profile_index() { return active_profile; }
 
+int zmk_ble_profile_index(const bt_addr_le_t *addr) {
+    for (int i = 0; i < ZMK_BLE_PROFILE_COUNT; i++) {
+        if (bt_addr_le_cmp(addr, &profiles[i].peer) == 0) {
+            return i;
+        }
+    }
+    return -ENODEV;
+}
+
 #if IS_ENABLED(CONFIG_SETTINGS)
 static void ble_save_profile_work(struct k_work *work) {
     settings_save_one("ble/active_profile", &active_profile, sizeof(active_profile));

app/src/events/hid_indicators_changed.c

@@ -0,0 +1,10 @@
+/*
+ * Copyright (c) 2022 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#include <zephyr/kernel.h>
+#include <zmk/events/hid_indicators_changed.h>
+
+ZMK_EVENT_IMPL(zmk_hid_indicators_changed);

app/src/hid_indicators.c

@@ -0,0 +1,69 @@
+/*
+ * Copyright (c) 2022 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#include <zephyr/kernel.h>
+#include <zephyr/logging/log.h>
+
+#include <zmk/ble.h>
+#include <zmk/endpoints.h>
+#include <zmk/hid_indicators.h>
+#include <zmk/events/hid_indicators_changed.h>
+#include <zmk/events/endpoint_changed.h>
+#include <zmk/split/bluetooth/central.h>
+
+LOG_MODULE_DECLARE(zmk, CONFIG_ZMK_LOG_LEVEL);
+
+static zmk_hid_indicators_t hid_indicators[ZMK_ENDPOINT_COUNT];
+
+zmk_hid_indicators_t zmk_hid_indicators_get_current_profile(void) {
+    return zmk_hid_indicators_get_profile(zmk_endpoints_selected());
+}
+
+zmk_hid_indicators_t zmk_hid_indicators_get_profile(struct zmk_endpoint_instance endpoint) {
+    const int profile = zmk_endpoint_instance_to_index(endpoint);
+    return hid_indicators[profile];
+}
+
+static void raise_led_changed_event(struct k_work *_work) {
+    const zmk_hid_indicators_t indicators = zmk_hid_indicators_get_current_profile();
+
+    ZMK_EVENT_RAISE(new_zmk_hid_indicators_changed(
+        (struct zmk_hid_indicators_changed){.indicators = indicators}));
+
+#if IS_ENABLED(CONFIG_ZMK_SPLIT_PERIPHERAL_HID_INDICATORS) && IS_ENABLED(CONFIG_ZMK_SPLIT_BLE)
+    zmk_split_bt_update_hid_indicator(indicators);
+#endif
+}
+
+static K_WORK_DEFINE(led_changed_work, raise_led_changed_event);
+
+void zmk_hid_indicators_set_profile(zmk_hid_indicators_t indicators,
+                                    struct zmk_endpoint_instance endpoint) {
+    int profile = zmk_endpoint_instance_to_index(endpoint);
+
+    // This write is not happening on the main thread. To prevent potential data races, every
+    // operation involving hid_indicators must be atomic. Currently, each function either reads
+    // or writes only one entry at a time, so it is safe to do these operations without a lock.
+    hid_indicators[profile] = indicators;
+
+    k_work_submit(&led_changed_work);
+}
+
+void zmk_hid_indicators_process_report(struct zmk_hid_led_report_body *report,
+                                       struct zmk_endpoint_instance endpoint) {
+    const zmk_hid_indicators_t indicators = (zmk_hid_indicators_t)report->leds;
+    zmk_hid_indicators_set_profile(indicators, endpoint);
+
+    LOG_DBG("Update HID indicators: endpoint=%d, indicators=%x", endpoint.transport, indicators);
+}
+
+static int profile_listener(const zmk_event_t *eh) {
+    raise_led_changed_event(NULL);
+    return 0;
+}
+
+static ZMK_LISTENER(profile_listener, profile_listener);
+static ZMK_SUBSCRIPTION(profile_listener, zmk_endpoint_changed);

app/src/hog.c

@@ -15,8 +15,12 @@ LOG_MODULE_DECLARE(zmk, CONFIG_ZMK_LOG_LEVEL);
 #include <zephyr/bluetooth/gatt.h>
 
 #include <zmk/ble.h>
+#include <zmk/endpoints_types.h>
 #include <zmk/hog.h>
 #include <zmk/hid.h>
+#if IS_ENABLED(CONFIG_ZMK_HID_INDICATORS)
+#include <zmk/hid_indicators.h>
+#endif // IS_ENABLED(CONFIG_ZMK_HID_INDICATORS)
 
 enum {
     HIDS_REMOTE_WAKE = BIT(0),
@@ -51,6 +55,15 @@ static struct hids_report input = {
     .type = HIDS_INPUT,
 };
 
+#if IS_ENABLED(CONFIG_ZMK_HID_INDICATORS)
+
+static struct hids_report led_indicators = {
+    .id = ZMK_HID_REPORT_ID_LEDS,
+    .type = HIDS_OUTPUT,
+};
+
+#endif // IS_ENABLED(CONFIG_ZMK_HID_INDICATORS)
+
 static struct hids_report consumer_input = {
     .id = ZMK_HID_REPORT_ID_CONSUMER,
     .type = HIDS_INPUT,
@@ -94,6 +107,34 @@ static ssize_t read_hids_input_report(struct bt_conn *conn, const struct bt_gatt
                              sizeof(struct zmk_hid_keyboard_report_body));
 }
 
+#if IS_ENABLED(CONFIG_ZMK_HID_INDICATORS)
+static ssize_t write_hids_leds_report(struct bt_conn *conn, const struct bt_gatt_attr *attr,
+                                      const void *buf, uint16_t len, uint16_t offset,
+                                      uint8_t flags) {
+    if (offset != 0) {
+        return BT_GATT_ERR(BT_ATT_ERR_INVALID_OFFSET);
+    }
+    if (len != sizeof(struct zmk_hid_led_report_body)) {
+        return BT_GATT_ERR(BT_ATT_ERR_INVALID_ATTRIBUTE_LEN);
+    }
+
+    struct zmk_hid_led_report_body *report = (struct zmk_hid_led_report_body *)buf;
+    int profile = zmk_ble_profile_index(bt_conn_get_dst(conn));
+    if (profile < 0) {
+        return BT_GATT_ERR(BT_ATT_ERR_UNLIKELY);
+    }
+
+    struct zmk_endpoint_instance endpoint = {.transport = ZMK_TRANSPORT_BLE,
+                                             .ble = {
+                                                 .profile_index = profile,
+                                             }};
+    zmk_hid_indicators_process_report(report, endpoint);
+
+    return len;
+}
+
+#endif // IS_ENABLED(CONFIG_ZMK_HID_INDICATORS)
+
 static ssize_t read_hids_consumer_input_report(struct bt_conn *conn,
                                                const struct bt_gatt_attr *attr, void *buf,
                                                uint16_t len, uint16_t offset) {
@@ -152,6 +193,7 @@ BT_GATT_SERVICE_DEFINE(
     BT_GATT_CCC(input_ccc_changed, BT_GATT_PERM_READ_ENCRYPT | BT_GATT_PERM_WRITE_ENCRYPT),
     BT_GATT_DESCRIPTOR(BT_UUID_HIDS_REPORT_REF, BT_GATT_PERM_READ_ENCRYPT, read_hids_report_ref,
                        NULL, &input),
+
     BT_GATT_CHARACTERISTIC(BT_UUID_HIDS_REPORT, BT_GATT_CHRC_READ | BT_GATT_CHRC_NOTIFY,
                            BT_GATT_PERM_READ_ENCRYPT, read_hids_consumer_input_report, NULL, NULL),
     BT_GATT_CCC(input_ccc_changed, BT_GATT_PERM_READ_ENCRYPT | BT_GATT_PERM_WRITE_ENCRYPT),
@@ -166,6 +208,15 @@ BT_GATT_SERVICE_DEFINE(
                        NULL, &mouse_input),
 #endif // IS_ENABLED(CONFIG_ZMK_MOUSE)
 
+#if IS_ENABLED(CONFIG_ZMK_HID_INDICATORS)
+    BT_GATT_CHARACTERISTIC(BT_UUID_HIDS_REPORT,
+                           BT_GATT_CHRC_READ | BT_GATT_CHRC_WRITE | BT_GATT_CHRC_WRITE_WITHOUT_RESP,
+                           BT_GATT_PERM_READ_ENCRYPT | BT_GATT_PERM_WRITE_ENCRYPT, NULL,
+                           write_hids_leds_report, NULL),
+    BT_GATT_DESCRIPTOR(BT_UUID_HIDS_REPORT_REF, BT_GATT_PERM_READ_ENCRYPT, read_hids_report_ref,
+                       NULL, &led_indicators),
+#endif // IS_ENABLED(CONFIG_ZMK_HID_INDICATORS)
+
     BT_GATT_CHARACTERISTIC(BT_UUID_HIDS_CTRL_POINT, BT_GATT_CHRC_WRITE_WITHOUT_RESP,
                            BT_GATT_PERM_WRITE, NULL, write_ctrl_point, &ctrl_point));
 
@@ -251,7 +302,7 @@ void send_consumer_report_callback(struct k_work *work) {
         }
 
         struct bt_gatt_notify_params notify_params = {
-            .attr = &hog_svc.attrs[10],
+            .attr = &hog_svc.attrs[9],
             .data = &report,
             .len = sizeof(report),
         };

app/src/split/Kconfig

@@ -20,6 +20,12 @@ config ZMK_SPLIT_BLE
 
 endchoice
 
+config ZMK_SPLIT_PERIPHERAL_HID_INDICATORS
+    bool "Peripheral HID Indicators"
+    depends on ZMK_HID_INDICATORS
+    help
+      Enable propogating the HID (LED) Indicator state to the split peripheral(s).
+
 #ZMK_SPLIT
 endif
 

app/src/split/bluetooth/central.c

@@ -27,6 +27,7 @@ LOG_MODULE_DECLARE(zmk, CONFIG_ZMK_LOG_LEVEL);
 #include <zmk/event_manager.h>
 #include <zmk/events/position_state_changed.h>
 #include <zmk/events/sensor_event.h>
+#include <zmk/hid_indicators_types.h>
 
 static int start_scanning(void);
 
@@ -46,6 +47,9 @@ struct peripheral_slot {
     struct bt_gatt_subscribe_params sensor_subscribe_params;
     struct bt_gatt_discover_params sub_discover_params;
     uint16_t run_behavior_handle;
+#if IS_ENABLED(CONFIG_ZMK_SPLIT_PERIPHERAL_HID_INDICATORS)
+    uint16_t update_hid_indicators;
+#endif // IS_ENABLED(CONFIG_ZMK_SPLIT_PERIPHERAL_HID_INDICATORS)
     uint8_t position_state[POSITION_STATE_DATA_LEN];
     uint8_t changed_positions[POSITION_STATE_DATA_LEN];
 };
@@ -131,6 +135,9 @@ int release_peripheral_slot(int index) {
     // Clean up previously discovered handles;
     slot->subscribe_params.value_handle = 0;
     slot->run_behavior_handle = 0;
+#if IS_ENABLED(CONFIG_ZMK_SPLIT_PERIPHERAL_HID_INDICATORS)
+    slot->update_hid_indicators = 0;
+#endif // IS_ENABLED(CONFIG_ZMK_SPLIT_PERIPHERAL_HID_INDICATORS)
 
     return 0;
 }
@@ -329,13 +336,23 @@ static uint8_t split_central_chrc_discovery_func(struct bt_conn *conn,
         slot->discover_params.uuid = NULL;
         slot->discover_params.start_handle = attr->handle + 2;
         slot->run_behavior_handle = bt_gatt_attr_value_handle(attr);
+#if IS_ENABLED(CONFIG_ZMK_SPLIT_PERIPHERAL_HID_INDICATORS)
+    } else if (!bt_uuid_cmp(((struct bt_gatt_chrc *)attr->user_data)->uuid,
+                            BT_UUID_DECLARE_128(ZMK_SPLIT_BT_UPDATE_HID_INDICATORS_UUID))) {
+        LOG_DBG("Found update HID indicators handle");
+        slot->update_hid_indicators = bt_gatt_attr_value_handle(attr);
+#endif // IS_ENABLED(CONFIG_ZMK_SPLIT_PERIPHERAL_HID_INDICATORS)
     }
 
-    bool subscribed = slot->run_behavior_handle && slot->subscribe_params.value_handle;
+    bool subscribed = (slot->run_behavior_handle && slot->subscribe_params.value_handle);
 #if ZMK_KEYMAP_HAS_SENSORS
     subscribed = subscribed && slot->sensor_subscribe_params.value_handle;
 #endif /* ZMK_KEYMAP_HAS_SENSORS */
 
+#if IS_ENABLED(CONFIG_ZMK_SPLIT_PERIPHERAL_HID_INDICATORS)
+    subscribed = subscribed && slot->update_hid_indicators;
+#endif // IS_ENABLED(CONFIG_ZMK_SPLIT_PERIPHERAL_HID_INDICATORS)
+
     return subscribed ? BT_GATT_ITER_STOP : BT_GATT_ITER_CONTINUE;
 }
 
@@ -685,6 +702,43 @@ int zmk_split_bt_invoke_behavior(uint8_t source, struct zmk_behavior_binding *bi
     return split_bt_invoke_behavior_payload(wrapper);
 }
 
+#if IS_ENABLED(CONFIG_ZMK_SPLIT_PERIPHERAL_HID_INDICATORS)
+
+static zmk_hid_indicators_t hid_indicators = 0;
+
+static void split_central_update_indicators_callback(struct k_work *work) {
+    zmk_hid_indicators_t indicators = hid_indicators;
+    for (int i = 0; i < ZMK_SPLIT_BLE_PERIPHERAL_COUNT; i++) {
+        if (peripherals[i].state != PERIPHERAL_SLOT_STATE_CONNECTED) {
+            continue;
+        }
+
+        if (peripherals[i].update_hid_indicators == 0) {
+            // It appears that sometimes the peripheral is considered connected
+            // before the GATT characteristics have been discovered. If this is
+            // the case, the update_hid_indicators handle will not yet be set.
+            continue;
+        }
+
+        int err = bt_gatt_write_without_response(peripherals[i].conn,
+                                                 peripherals[i].update_hid_indicators, &indicators,
+                                                 sizeof(indicators), true);
+
+        if (err) {
+            LOG_ERR("Failed to write HID indicator characteristic (err %d)", err);
+        }
+    }
+}
+
+static K_WORK_DEFINE(split_central_update_indicators, split_central_update_indicators_callback);
+
+int zmk_split_bt_update_hid_indicator(zmk_hid_indicators_t indicators) {
+    hid_indicators = indicators;
+    return k_work_submit_to_queue(&split_central_split_run_q, &split_central_update_indicators);
+}
+
+#endif // IS_ENABLED(CONFIG_ZMK_SPLIT_PERIPHERAL_HID_INDICATORS)
+
 int zmk_split_bt_central_init(const struct device *_arg) {
     k_work_queue_start(&split_central_split_run_q, split_central_split_run_q_stack,
                        K_THREAD_STACK_SIZEOF(split_central_split_run_q_stack),

app/src/split/bluetooth/service.c

@@ -21,6 +21,11 @@ LOG_MODULE_DECLARE(zmk, CONFIG_ZMK_LOG_LEVEL);
 #include <zmk/matrix.h>
 #include <zmk/split/bluetooth/uuid.h>
 #include <zmk/split/bluetooth/service.h>
+
+#if IS_ENABLED(CONFIG_ZMK_SPLIT_PERIPHERAL_HID_INDICATORS)
+#include <zmk/events/hid_indicators_changed.h>
+#endif // IS_ENABLED(CONFIG_ZMK_SPLIT_PERIPHERAL_HID_INDICATORS)
+
 #include <zmk/events/sensor_event.h>
 #include <zmk/sensors.h>
 
@@ -105,6 +110,34 @@ static void split_svc_pos_state_ccc(const struct bt_gatt_attr *attr, uint16_t va
     LOG_DBG("value %d", value);
 }
 
+#if IS_ENABLED(CONFIG_ZMK_SPLIT_PERIPHERAL_HID_INDICATORS)
+
+static zmk_hid_indicators_t hid_indicators = 0;
+
+static void split_svc_update_indicators_callback(struct k_work *work) {
+    LOG_DBG("Raising HID indicators changed event: %x", hid_indicators);
+    ZMK_EVENT_RAISE(new_zmk_hid_indicators_changed(
+        (struct zmk_hid_indicators_changed){.indicators = hid_indicators}));
+}
+
+static K_WORK_DEFINE(split_svc_update_indicators_work, split_svc_update_indicators_callback);
+
+static ssize_t split_svc_update_indicators(struct bt_conn *conn, const struct bt_gatt_attr *attr,
+                                           const void *buf, uint16_t len, uint16_t offset,
+                                           uint8_t flags) {
+    if (offset + len > sizeof(zmk_hid_indicators_t)) {
+        return BT_GATT_ERR(BT_ATT_ERR_INVALID_OFFSET);
+    }
+
+    memcpy((uint8_t *)&hid_indicators + offset, buf, len);
+
+    k_work_submit(&split_svc_update_indicators_work);
+
+    return len;
+}
+
+#endif // IS_ENABLED(CONFIG_ZMK_SPLIT_PERIPHERAL_HID_INDICATORS)
+
 BT_GATT_SERVICE_DEFINE(
     split_svc, BT_GATT_PRIMARY_SERVICE(BT_UUID_DECLARE_128(ZMK_SPLIT_BT_SERVICE_UUID)),
     BT_GATT_CHARACTERISTIC(BT_UUID_DECLARE_128(ZMK_SPLIT_BT_CHAR_POSITION_STATE_UUID),
@@ -122,6 +155,11 @@ BT_GATT_SERVICE_DEFINE(
                            split_svc_sensor_state, NULL, &last_sensor_event),
     BT_GATT_CCC(split_svc_sensor_state_ccc, BT_GATT_PERM_READ_ENCRYPT | BT_GATT_PERM_WRITE_ENCRYPT),
 #endif /* ZMK_KEYMAP_HAS_SENSORS */
+#if IS_ENABLED(CONFIG_ZMK_SPLIT_PERIPHERAL_HID_INDICATORS)
+    BT_GATT_CHARACTERISTIC(BT_UUID_DECLARE_128(ZMK_SPLIT_BT_UPDATE_HID_INDICATORS_UUID),
+                           BT_GATT_CHRC_WRITE_WITHOUT_RESP, BT_GATT_PERM_WRITE_ENCRYPT, NULL,
+                           split_svc_update_indicators, NULL),
+#endif // IS_ENABLED(CONFIG_ZMK_SPLIT_PERIPHERAL_HID_INDICATORS)
 );
 
 K_THREAD_STACK_DEFINE(service_q_stack, CONFIG_ZMK_SPLIT_BLE_PERIPHERAL_STACK_SIZE);

app/src/usb_hid.c

@@ -13,6 +13,9 @@
 #include <zmk/usb.h>
 #include <zmk/hid.h>
 #include <zmk/keymap.h>
+#if IS_ENABLED(CONFIG_ZMK_HID_INDICATORS)
+#include <zmk/hid_indicators.h>
+#endif // IS_ENABLED(CONFIG_ZMK_HID_INDICATORS)
 #include <zmk/event_manager.h>
 
 LOG_MODULE_DECLARE(zmk, CONFIG_ZMK_LOG_LEVEL);
@@ -83,12 +86,44 @@ static int get_report_cb(const struct device *dev, struct usb_setup_packet *setu
     return 0;
 }
 
+static int set_report_cb(const struct device *dev, struct usb_setup_packet *setup, int32_t *len,
+                         uint8_t **data) {
+    if ((setup->wValue & HID_GET_REPORT_TYPE_MASK) != HID_REPORT_TYPE_OUTPUT) {
+        LOG_ERR("Unsupported report type %d requested",
+                (setup->wValue & HID_GET_REPORT_TYPE_MASK) >> 8);
+        return -ENOTSUP;
+    }
+
+    switch (setup->wValue & HID_GET_REPORT_ID_MASK) {
+#if IS_ENABLED(CONFIG_ZMK_HID_INDICATORS)
+    case ZMK_HID_REPORT_ID_LEDS:
+        if (*len != sizeof(struct zmk_hid_led_report)) {
+            LOG_ERR("LED set report is malformed: length=%d", *len);
+            return -EINVAL;
+        } else {
+            struct zmk_hid_led_report *report = (struct zmk_hid_led_report *)*data;
+            struct zmk_endpoint_instance endpoint = {
+                .transport = ZMK_TRANSPORT_USB,
+            };
+            zmk_hid_indicators_process_report(&report->body, endpoint);
+        }
+        break;
+#endif // IS_ENABLED(CONFIG_ZMK_HID_INDICATORS)
+    default:
+        LOG_ERR("Invalid report ID %d requested", setup->wValue & HID_GET_REPORT_ID_MASK);
+        return -EINVAL;
+    }
+
+    return 0;
+}
+
 static const struct hid_ops ops = {
 #if IS_ENABLED(CONFIG_ZMK_USB_BOOT)
     .protocol_change = set_proto_cb,
 #endif
     .int_in_ready = in_ready_cb,
     .get_report = get_report_cb,
+    .set_report = set_report_cb,
 };
 
 static int zmk_usb_hid_send_report(const uint8_t *report, size_t len) {

docs/docs/config/system.md

@@ -23,7 +23,8 @@ Definition file: [zmk/app/Kconfig](https://github.com/zmkfirmware/zmk/blob/main/
 ### HID
 
 | Config                                | Type | Description                                                    | Default |
-| ------------------------------------- | ---- | ------------------------------------------------- | ------- |
+| ------------------------------------- | ---- | -------------------------------------------------------------- | ------- |
+| `CONFIG_ZMK_HID_INDICATORS`           | bool | Enable reciept of HID/LED indicator state from connected hosts | n       |
 | `CONFIG_ZMK_HID_CONSUMER_REPORT_SIZE` | int  | Number of consumer keys simultaneously reportable              | 6       |
 
 Exactly zero or one of the following options may be set to `y`. The first is used if none are set.
@@ -92,8 +93,9 @@ Note that `CONFIG_BT_MAX_CONN` and `CONFIG_BT_MAX_PAIRED` should be set to the s
 Following split keyboard settings are defined in [zmk/app/src/split/Kconfig](https://github.com/zmkfirmware/zmk/blob/main/app/src/split/Kconfig) (generic) and [zmk/app/src/split/Kconfig](https://github.com/zmkfirmware/zmk/blob/main/app/src/split/bluetooth/Kconfig) (bluetooth).
 
 | Config                                                | Type | Description                                                              | Default |
-| ----------------------------------------------------- | ---- | ----------------------------------------------------------------------- | ------- |
+| ----------------------------------------------------- | ---- | ------------------------------------------------------------------------ | ------- |
 | `CONFIG_ZMK_SPLIT`                                    | bool | Enable split keyboard support                                            | n       |
+| `CONFIG_ZMK_SPLIT_PERIPHERAL_HID_INDICATORS`          | bool | Enable split keyboard support for passing indicator state to peripherals | n       |
 | `CONFIG_ZMK_SPLIT_BLE`                                | bool | Use BLE to communicate between split keyboard halves                     | y       |
 | `CONFIG_ZMK_SPLIT_ROLE_CENTRAL`                       | bool | `y` for central device, `n` for peripheral                               |         |
 | `CONFIG_ZMK_SPLIT_BLE_CENTRAL_POSITION_QUEUE_SIZE`    | int  | Max number of key state events to queue when received from peripherals   | 5       |