Advanced Capability Issues

What causes the error "_iotx_linkkit_upstream_sync_callback_list_remove(158): Message Found: 3, Delete It" when a sub-device connects?

This error occurs because a blocking operation in the callback function prevents the SDK's internal API from retrieving the required data to bring the sub-device online. Check your callback function to ensure that it does not contain any blocking operations.

After a gateway goes offline, its sub-devices also go offline automatically. Why don't the sub-devices automatically come online when the gateway comes back online?

Sub-devices connect to IoT Platform through a gateway proxy. When the gateway goes offline, the sub-devices also go offline automatically.

Gateways and sub-devices have different reconnection mechanisms and use different methods to come back online.

• A gateway device is a directly connected device that establishes a persistent connection with IoT Platform. The default reconnection mechanism in the SDK allows the device to automatically reconnect to IoT Platform if the connection is lost under specific conditions.
• Sub-devices go online and offline by calling the logon and logoff APIs and do not connect directly to IoT Platform. You must implement the reconnection logic for sub-devices. For example:
  1. Detect that the gateway is offline in the callback for a disconnected MQTT persistent connection.
  2. After the gateway goes offline, the sub-devices also go offline.
  3. When the gateway successfully reconnects, call the logon API from the MQTT persistent connection callback to bring the sub-devices back online asynchronously.

Why is the process of bringing sub-devices online slow when there are many of them?

SDK v3.x and v2.3.0 bring sub-devices online sequentially. Therefore, the registration or online process is slow for many sub-devices.

The latest version of the SDK supports bringing sub-devices online in batches. We recommend that you use the latest version of the SDK. For more information, see Gateways and sub-devices.

How do I resolve the error "The resource count exceeds limit, cur 255, max 255" when bringing a sub-device online?

This error indicates that the number of registered topics for the sub-device has reached the limit. To resolve this issue, modify the code in the following two locations:

• ./src/protocol/coap/local/CoAPServer.c: param.res_maxcount = 255.
• ./src/protocol/coap/local/CoAPExport.h file, in the CoAPInitParam struct, change the type of res_maxcount to unsigned int.