drv/bluetooth_stm32_cc2640: work around broadcast lock up

The Bluetooth chips on the Technic and City hubs seem to lock up if
the advertisement date is updated too many times. So far, we have only
found one condition where this doesn't happen. The Bluetooth chip
can't be connected to any other devices and advertising has to be
stopped and restarted between each update. This is quite limiting,
but seems to be the best we can do for now.

Issue: pybricks/support#1095

lib/pbio/drv/bluetooth/bluetooth_stm32_cc2640.c

@@ -827,6 +827,28 @@ static PT_THREAD(broadcast_task(struct pt *pt, pbio_task_t *task)) {
         PT_EXIT(pt);
     }
 
+    // Unfortunately, the Bluetooth chip on the Technic and City hubs will
+    // eventually crash if we keep updating the advertising data when connected
+    // to something else at the same time. So we can't permit this operation
+    // when connected to something else.
+    if (conn_handle != NO_CONNECTION || remote_handle != NO_CONNECTION) {
+        task->status = PBIO_ERROR_INVALID_OP;
+        PT_EXIT(pt);
+    }
+
+    // Even when not connected to something else, the Bluetooth chip will still
+    // eventually lock up unless we stop and restart advertising.
+    if (is_broadcasting) {
+        PT_WAIT_WHILE(pt, write_xfer_size);
+        GAP_endDiscoverable();
+        PT_WAIT_UNTIL(pt, hci_command_status);
+
+        if (read_buf[8] == bleSUCCESS) {
+            // wait for discovery cancel done event
+            PT_WAIT_UNTIL(pt, hci_command_complete);
+        }
+    }
+
     PT_WAIT_WHILE(pt, write_xfer_size);
     GAP_updateAdvertisingData(GAP_AD_TYPE_ADVERTISEMENT_DATA, value->size, value->data);
     PT_WAIT_UNTIL(pt, hci_command_status);
@@ -865,34 +887,34 @@ static PT_THREAD(broadcast_task(struct pt *pt, pbio_task_t *task)) {
         PT_WAIT_UNTIL(pt, hci_command_status);
         // ignoring response data
 
-        PT_WAIT_WHILE(pt, write_xfer_size);
-        GAP_makeDiscoverable(
-            #if PBDRV_CONFIG_BLUETOOTH_STM32_CC2640_QUIRK_BROKEN_NONCONN_IND
-            // City hub fails to send non-connectable advertisements so we
-            // have to use the wrong advertisement type to get it to actually
-            // send something over the air.
-            ADV_IND,
-            #else
-            // Technic hub will send non-connectable advertisements only if
-            // it is connected to something else, otherwise we need the same
-            // hack as the City hub.
-            (conn_handle == NO_CONNECTION && remote_handle == NO_CONNECTION) ? ADV_IND : ADV_NONCONN_IND,
-            #endif
-            GAP_INITIATOR_ADDR_TYPE_PRIVATE_NON_RESOLVE, NULL,
-            GAP_CHANNEL_MAP_ALL, GAP_FILTER_POLICY_SCAN_ANY_CONNECT_ANY);
-        PT_WAIT_UNTIL(pt, hci_command_status);
-
-        if (read_buf[8] != bleSUCCESS) {
-            task->status = ble_error_to_pbio_error(read_buf[8]);
-            PT_EXIT(pt);
-        }
+        is_broadcasting = true;
+    }
 
-        // wait for make discoverable done event
-        PT_WAIT_UNTIL(pt, hci_command_complete);
+    PT_WAIT_WHILE(pt, write_xfer_size);
+    GAP_makeDiscoverable(
+        #if PBDRV_CONFIG_BLUETOOTH_STM32_CC2640_QUIRK_BROKEN_NONCONN_IND
+        // City hub fails to send non-connectable advertisements so we
+        // have to use the wrong advertisement type to get it to actually
+        // send something over the air.
+        ADV_IND,
+        #else
+        // Technic hub will send non-connectable advertisements only if
+        // it is connected to something else, otherwise we need the same
+        // hack as the City hub.
+        (conn_handle == NO_CONNECTION && remote_handle == NO_CONNECTION) ? ADV_IND : ADV_NONCONN_IND,
+        #endif
+        GAP_INITIATOR_ADDR_TYPE_PRIVATE_NON_RESOLVE, NULL,
+        GAP_CHANNEL_MAP_ALL, GAP_FILTER_POLICY_SCAN_ANY_CONNECT_ANY);
+    PT_WAIT_UNTIL(pt, hci_command_status);
 
-        is_broadcasting = true;
+    if (read_buf[8] != bleSUCCESS) {
+        task->status = ble_error_to_pbio_error(read_buf[8]);
+        PT_EXIT(pt);
     }
 
+    // wait for make discoverable done event
+    PT_WAIT_UNTIL(pt, hci_command_complete);
+
     task->status = PBIO_SUCCESS;
 
     PT_END(pt);