Split from STM32U5G9J DK2 + 4G Module (USB CDC ECM) not detecting USB device - this is a different question.
这个工程是使用STM32U575 + EC800Z 4G模块，实现ecm上网的。
工程测试了sntp，ping，均能正常工作。
dns解析运行一段时间后会解析失败，还未去找原因。
在这个例子的基础上，另外的工程中使用了MQTT协议，能正常工作，但是如果MQTT消息在超过1000字节左右的时候，会频繁掉线，有时候甚至无法再连上服务器的问题（ERROR: mqtt client connect error: 0x10005），通过日志查看发现网络包也不没有了，一直在查找相关问题，目前还未解决。
Google Translate:
This project uses STM32U575 + EC800Z 4G module to achieve ecm Internet access.
The project tested sntp and ping, both of which worked properly. However, DNS resolution would fail after a while, and the cause has yet to be determined.
Building on this example, another project used the MQTT protocol, which also worked properly. However, if the MQTT message length exceeded approximately 1000 bytes, the connection would frequently drop, sometimes even failing to connect to the server (ERROR: mqtt client connect error: 0x10005). Checking the logs revealed that network packets were also missing.
We have been searching for related issues, but have yet to resolve them.
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