feat(endpoints): clear HID report on endpoint change

This prevents stuck keys when switching endpoints by clearing
everything in the HID report and sending one last report before
switching to the new endpoint.

app/include/zmk/hid.h

@@ -165,9 +165,11 @@ int zmk_hid_register_mods(zmk_mod_flags modifiers);
 int zmk_hid_unregister_mods(zmk_mod_flags modifiers);
 int zmk_hid_keypad_press(zmk_key key);
 int zmk_hid_keypad_release(zmk_key key);
+void zmk_hid_keypad_clear();
 
 int zmk_hid_consumer_press(zmk_key key);
 int zmk_hid_consumer_release(zmk_key key);
+void zmk_hid_consumer_clear();
 
 struct zmk_hid_keypad_report *zmk_hid_get_keypad_report();
 struct zmk_hid_consumer_report *zmk_hid_get_consumer_report();

app/src/endpoints.c

@@ -126,11 +126,21 @@ static enum endpoint get_selected_endpoint() {
     return ENDPOINT_USB;
 }
 
+static void disconnect_current_endpoint() {
+    zmk_hid_keypad_clear();
+    zmk_hid_consumer_clear();
+
+    zmk_endpoints_send_report(USAGE_KEYPAD);
+    zmk_endpoints_send_report(USAGE_CONSUMER);
+}
+
 static int endpoint_listener(const struct zmk_event_header *eh) {
     enum endpoint new_endpoint = get_selected_endpoint();
 
     if (new_endpoint != current_endpoint) {
-        // TODO: send null report on previous endpoint
+        /* Cancel all current keypresses so keys don't stay held on the old endpoint. */
+        disconnect_current_endpoint();
+
         current_endpoint = new_endpoint;
         LOG_INF("Endpoint changed: %d", current_endpoint);
     }

app/src/hid.c

@@ -94,6 +94,8 @@ int zmk_hid_keypad_release(zmk_key code) {
     return 0;
 };
 
+void zmk_hid_keypad_clear() { memset(&kp_report.body, 0, sizeof(kp_report.body)); }
+
 int zmk_hid_consumer_press(zmk_key code) {
     TOGGLE_CONSUMER(0U, code);
     return 0;
@@ -104,6 +106,8 @@ int zmk_hid_consumer_release(zmk_key code) {
     return 0;
 };
 
+void zmk_hid_consumer_clear() { memset(&consumer_report.body, 0, sizeof(consumer_report.body)); }
+
 struct zmk_hid_keypad_report *zmk_hid_get_keypad_report() {
     return &kp_report;
 }