gap: gap_enable_link_watchdog() uses automatic flush timeout to disconnect if data cannot be sent

CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 ### Added
 - HCI: ENABLE_HCI_SERIALIZED_CONTROLLER_OPERATIONS serializes Inquiry, Remote Name Request and Create Connection operations
 - GAP: support extended advertising with ENABLE_LE_EXTENDED_ADVERTISING
+- GAP: gap_enable_link_watchdog() uses automatic flush timeout to disconnect if data cannot be sent
 - ATT DB: provide gatt_server_get_handle_range_for_service_with_uuid16 to find included service within handle range
 - GATT Service: Audio Input Control Service Server (AICS 1.0)
 - GATT Service: Volume Control Service Server (VCS 1.0)

src/gap.h

@@ -270,6 +270,13 @@ void gap_set_allow_role_switch(bool allow_role_switch);
  */
 void gap_set_link_supervision_timeout(uint16_t link_supervision_timeout);
 
+/**
+ * @brief Enable link watchdog. If no ACL packet is sent within timeout_ms, the link will get disconnected
+ * note: current implementation uses the automatic flush timeout controller feature with a max timeout of 1.28s
+ * @param timeout_ms
+ */
+void gap_enable_link_watchdog(uint16_t timeout_ms);
+
 /**
  * @brief Enable/disable bonding. Default is enabled.
  * @param enabled
@@ -1021,7 +1028,7 @@ uint8_t gap_ssp_io_capabilities_negative(const bd_addr_t addr);
 
 /**
  * Send Link Key Reponse
- * @note Link Key (Negative) Reply is sent automaticallyu unless ENABLE_EXPLICIT_LINK_KEY_RESPONSE
+ * @note Link Key (Negative) Reply is sent automatically unless ENABLE_EXPLICIT_LINK_KEY_RESPONSE
  * @param addr
  * @param link_key
  * @param type or INVALID_LINK_KEY if link key not available

src/hci.c

@@ -2887,6 +2887,16 @@ static void event_handler(uint8_t *packet, uint16_t size){
         }
 
 #ifdef ENABLE_CLASSIC
+        case HCI_EVENT_FLUSH_OCCURRED:
+            // flush occurs only if automatic flush has been enabled by gap_enable_link_watchdog()
+            handle = hci_event_flush_occurred_get_handle(packet);
+            conn = hci_connection_for_handle(handle);
+            if (conn) {
+                log_info("Flush occurred, disconnect 0x%04x", handle);
+                conn->state = SEND_DISCONNECT;
+            }
+            break;
+
         case HCI_EVENT_INQUIRY_COMPLETE:
             if (hci_stack->inquiry_state == GAP_INQUIRY_STATE_ACTIVE){
                 hci_stack->inquiry_state = GAP_INQUIRY_STATE_IDLE;
@@ -2958,6 +2968,11 @@ static void event_handler(uint8_t *packet, uint16_t size){
                         connectionSetAuthenticationFlags(conn, AUTH_FLAG_WRITE_SUPERVISION_TIMEOUT);
                     }
 
+                    // queue write automatic flush timeout
+                    if (hci_stack->automatic_flush_timeout != 0){
+                        conn->gap_connection_tasks |= GAP_CONNECTION_TASK_WRITE_AUTOMATIC_FLUSH_TIMEOUT;
+                    }
+
                     // restart timer
                     btstack_run_loop_set_timer(&conn->timeout, HCI_CONNECTION_TIMEOUT_MS);
                     btstack_run_loop_add_timer(&conn->timeout);
@@ -3987,6 +4002,14 @@ void gap_set_link_supervision_timeout(uint16_t link_supervision_timeout){
     hci_stack->link_supervision_timeout = link_supervision_timeout;
 }
 
+void gap_enable_link_watchdog(uint16_t timeout_ms){
+    hci_stack->automatic_flush_timeout = btstack_min(timeout_ms, 1280) * 8 / 5; // divide by 0.625
+}
+
+uint16_t hci_automatic_flush_timeout(void){
+    return hci_stack->automatic_flush_timeout;
+}
+
 void hci_disable_l2cap_timeout_check(void){
     disable_l2cap_timeouts = 1;
 }
@@ -5649,6 +5672,14 @@ static bool hci_run_general_pending_commands(void){
             hci_send_cmd(&hci_switch_role_command, connection->address, role);
             return true;
         }
+
+        if (connection->gap_connection_tasks != 0){
+            if ((connection->gap_connection_tasks & GAP_CONNECTION_TASK_WRITE_AUTOMATIC_FLUSH_TIMEOUT) != 0){
+                connection->gap_connection_tasks &= ~GAP_CONNECTION_TASK_WRITE_AUTOMATIC_FLUSH_TIMEOUT;
+                hci_send_cmd(&hci_write_automatic_flush_timeout, connection->con_handle, hci_stack->automatic_flush_timeout);
+                return true;
+            }
+        }
 #endif
 
 #ifdef ENABLE_BLE

src/hci.h

@@ -227,6 +227,9 @@ typedef enum {
 
 } hci_authentication_flags_t;
 
+// GAP Connection Tasks
+#define GAP_CONNECTION_TASK_WRITE_AUTOMATIC_FLUSH_TIMEOUT 0x0001u
+
 /**
  * Connection State 
  */
@@ -596,7 +599,10 @@ typedef struct {
 #endif /* ENABLE_CLASSIC */
 
     // authentication and other errands
-    uint32_t authentication_flags;
+    uint16_t authentication_flags;
+
+    // gap connection tasks, see GAP_CONNECTION_TASK_x
+    uint16_t gap_connection_tasks;
 
     btstack_timer_source_t timeout;
 
@@ -905,7 +911,10 @@ typedef struct {
 
     // Errata-11838 mandates 7 bytes for GAP Security Level 1-3, we use 16 as default
     uint8_t            gap_required_encyrption_key_size;
+
     uint16_t           link_supervision_timeout;
+    uint16_t           automatic_flush_timeout;
+
     gap_security_level_t gap_security_level;
     gap_security_level_t gap_minimal_service_security_level;
     gap_security_mode_t  gap_security_mode;
@@ -1356,6 +1365,11 @@ uint16_t hci_usable_acl_packet_types(void);
  */
 bool hci_non_flushable_packet_boundary_flag_supported(void);
 
+/**
+ * Return current automatic flush timeout setting
+ */
+uint16_t hci_automatic_flush_timeout(void);
+
 /**
  * Check if remote supported features query has completed
  */

src/l2cap.c

@@ -1389,7 +1389,7 @@ static void l2cap_rtx_timeout(btstack_timer_source_t * ts){
 }
 
 static uint8_t l2cap_classic_packet_boundary_flag(void){
-    return hci_non_flushable_packet_boundary_flag_supported() ? 0x00 : 0x02;
+    return (hci_non_flushable_packet_boundary_flag_supported() && (hci_automatic_flush_timeout() == 0)) ? 0x00 : 0x02;
 }
 #endif