feat(split): Increase split interval during idle

app/src/split/bluetooth/CMakeLists.txt

@@ -7,6 +7,7 @@ if (NOT CONFIG_ZMK_SPLIT_ROLE_CENTRAL)
 endif()
 if (CONFIG_ZMK_SPLIT_ROLE_CENTRAL)
   target_sources(app PRIVATE central.c)
+  target_sources_ifdef(CONFIG_ZMK_SPLIT_BLE_PREF_IDLE app PRIVATE central_idle.c)
 endif()
 
 if (CONFIG_ZMK_SPLIT_BLE_CENTRAL_BATTERY_LEVEL_PROXY)

app/src/split/bluetooth/Kconfig

@@ -74,6 +74,26 @@ config ZMK_SPLIT_BLE_PREF_TIMEOUT
     int "Supervision timeout to use for split central/peripheral connection"
     default 400
 
+config ZMK_SPLIT_BLE_PREF_IDLE
+    bool "Set slower split peripheral BLE params on idle to save power"
+    default y
+
+if ZMK_SPLIT_BLE_PREF_IDLE
+
+config ZMK_SPLIT_BLE_PREF_IDLE_INT
+    int "Idle connection interval to use for split central/peripheral connection"
+    default 18
+
+config ZMK_SPLIT_BLE_PREF_IDLE_LATENCY
+    int "Idle latency to use for split central/peripheral connection"
+    default 10
+
+config ZMK_SPLIT_BLE_PREF_IDLE_TIMEOUT
+    int "Idle supervision timeout to use for split central/peripheral connection"
+    default 400
+
+endif # ZMK_SPLIT_BLE_PREF_IDLE
+
 endif # ZMK_SPLIT_ROLE_CENTRAL
 
 if !ZMK_SPLIT_ROLE_CENTRAL

app/src/split/bluetooth/central_idle.c

@@ -0,0 +1,86 @@
+/*
+ * Copyright (c) 2025 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#include <zephyr/logging/log.h>
+LOG_MODULE_DECLARE(zmk, CONFIG_ZMK_LOG_LEVEL);
+
+#include <zephyr/bluetooth/bluetooth.h>
+#include <zephyr/bluetooth/conn.h>
+
+#include <zmk/event_manager.h>
+#include <zmk/events/activity_state_changed.h>
+
+static void set_sleep_params(struct bt_conn *conn, void *data) {
+    struct bt_conn_info info;
+
+    bt_conn_get_info(conn, &info);
+
+    if (info.role == BT_CONN_ROLE_CENTRAL && info.state == BT_CONN_STATE_CONNECTED) {
+        int err =
+            bt_conn_le_param_update(conn, BT_LE_CONN_PARAM(CONFIG_ZMK_SPLIT_BLE_PREF_IDLE_INT,
+                                                           CONFIG_ZMK_SPLIT_BLE_PREF_IDLE_INT,
+                                                           CONFIG_ZMK_SPLIT_BLE_PREF_IDLE_LATENCY,
+                                                           CONFIG_ZMK_SPLIT_BLE_PREF_IDLE_TIMEOUT));
+
+        if (err) {
+            LOG_DBG("Failed to set idle params on split connection: %d", err);
+        }
+    }
+}
+
+static void set_wake_params(struct bt_conn *conn, void *data) {
+    struct bt_conn_info info;
+
+    bt_conn_get_info(conn, &info);
+
+    if (info.role == BT_CONN_ROLE_CENTRAL && info.state == BT_CONN_STATE_CONNECTED) {
+        int err = bt_conn_le_param_update(
+            conn,
+            BT_LE_CONN_PARAM(CONFIG_ZMK_SPLIT_BLE_PREF_INT, CONFIG_ZMK_SPLIT_BLE_PREF_INT,
+                             CONFIG_ZMK_SPLIT_BLE_PREF_LATENCY, CONFIG_ZMK_SPLIT_BLE_PREF_TIMEOUT));
+
+        if (err) {
+            LOG_DBG("Failed to set active params on split connection: %d", err);
+        }
+    }
+}
+
+static void sleep_all(void) {
+    LOG_DBG("Setting idle connection parameters on peripherals");
+
+    bt_conn_foreach(BT_CONN_TYPE_LE, set_sleep_params, NULL);
+}
+
+static void wake_all(void) {
+    LOG_DBG("Waking up from idle connection parameters on peripherals");
+
+    bt_conn_foreach(BT_CONN_TYPE_LE, set_wake_params, NULL);
+}
+
+static int central_idle_listener(const zmk_event_t *eh) {
+    struct zmk_activity_state_changed *ev = as_zmk_activity_state_changed(eh);
+    if (ev == NULL) {
+        return -ENOTSUP;
+    }
+
+    switch (ev->state) {
+    case ZMK_ACTIVITY_ACTIVE:
+        wake_all();
+        break;
+    case ZMK_ACTIVITY_IDLE:
+        sleep_all();
+        break;
+    case ZMK_ACTIVITY_SLEEP:
+        break;
+    default:
+        LOG_WRN("Unhandled activity state: %d", ev->state);
+        return -EINVAL;
+    }
+    return 0;
+}
+
+ZMK_LISTENER(central_idle, central_idle_listener);
+ZMK_SUBSCRIPTION(central_idle, zmk_activity_state_changed);

app/west.yml

@@ -4,10 +4,12 @@ manifest:
       url-base: https://github.com/zephyrproject-rtos
     - name: zmkfirmware
       url-base: https://github.com/zmkfirmware
+    - name: carrefinho
+      url-base: https://github.com/carrefinho
   projects:
     - name: zephyr
-      remote: zmkfirmware
-      revision: v4.1.0+zmk-fixes
+      remote: carrefinho
+      revision: v4.1.0+zmk-fixes+split-conn-fix
       clone-depth: 1
       import:
         name-blocklist: